Potato Agronomy Research

The potato agronomy trials are designed to evaluate some of the basic agronomic characteristics and management parameters required for newly released cultivars of interest to Saskatchewan’s potato industry, and to evaluate the performance of new potato varieties under Saskatchewan growing conditions.

Trials are conducted on the Plant Sciences Department Potato Research plots located in Saskatoon.

Agronomy of New Potato Lines - 2010 Growing Season PDF
Several trials evaluate the impact of N-fertility, crop maturity, irrigation, in-row spacing, and post emergent herbicide application on potato yield and quality. Varieties tested: AC Pacific Russet, Norland, Milva, Blazer, Alpine, Modoc, Russet Norkotah, Russet Burbank, Shepody.

Agronomy of New Potato Lines - 2009 Growing Season PDF
Several trials evaluate the impact of N-fertility, crop maturity, irrigation, in-row spacing, and post emergent herbicide application on potato yield and quality. Varieties tested: AC Peregrine, O'Pearl, Shepody, Norland, Russet Norkotah, Russet Burbank, Milva.

Agronomy of New Potato Lines - 2008 Growing Season PDF
Several trials evaluate the impact of N-fertility, crop maturity, irrigation, in-row spacing, and post emergent herbicide application on potato yield and quality. Varieties tested: AC Peregrine, AC Pacific Russet, Gemstar, Dakota Jewel, CV 89075-1, Norland, Russet Norkotah, Russet Burbank.

Agronomy of New Potato Lines - 2007 Growing Season PDF
Several trials evaluate the impact of N-fertility, crop maturity, irrigation, in-row spacing, and post emergent herbicide application on potato yield and quality. Varieties tested: AC Peregrine, AC Pacific Russet, Gemstar, Dakota Jewel, CV 89075-1, Norland, Russet Norkotah, Russet Burbank.

Agronomy of New Potato Lines - 2006 Growing Season PDF
Several trials evaluate the impact of N-fertility, crop maturity, irrigation, in-row spacing, and post emergent herbicide application on potato yield and quality. Varieties tested: AC Peregrine, AC Pacific Russet, Gemstar, Dakota Jewel, CV 89075-1, Norland, Russet Norkotah, Russet Burbank.

Agronomy of New Potato Lines - 2005 Growing Season PDF
Several trials evaluate the impact of N-fertility, crop maturity, irrigation and in-row spacing on potato yield and quality. Varieties tested: AC Peregrine, AC Pacific Russet, Gemstar, Russet Norkotah, Russet Burbank, Norland, CV 89023-2, CV 89075-1, and V0865-1

Agronomy of New Potato Lines - 2004 Growing Season PDF
Varieties tested: Norland, AC Peregrine, CV 89023-2, CV 89075-1, Russet Norkotah, Russet Burbank, AC Pacific Russet, GemStar, VO865-1.

Agronomics of New Potato Cultivars - 2001 Growing Season PDF
Varieties tested: AC Peregrine Red, Cherry Red, Umatilla, Gem Russet.

Agronomics of New Potato Cultivars - 2000 Growing Season PDF
Varieties tested: AC Peregrine Red, Cherry Red, Umatilla, Gem Russet, Legend Russet.

Agronomics of New Potato Cultivars - 1999 Growing Season PDF
Varieties tested: ND2937-3, Umatilla, Gem Russet

Agronomics of New Red-Skinned Potato Cultivars - 1999 Growing Season PDF
This trial evaluated the impact of seedpiece spacing on the yields and tuber size distribution of Norland, Cherry Red, and VO498-4 under irrigated and dryland conditions.

Agronomics of New Red-Skinned Potato Cultivars - 1998 Growing Season PDF
This trial evaluated the impact of seedpiece spacing on the yields and tuber size distribution of Norland, NorDonna and Cherry Red under irrigated and dryland conditions.

Other Agronomy Trials

Influence of plant growth regulators on skin color and scab diseases of red-skinned potatoes
Presents the results of a 3 year study on the potential to use foliar-applied plant growth regulators to improve skin color and enhabce common scab resistance of red-skinned potatoes.

Changes in Vine Moisture Content and Yields Following Chemical Desiccation of Potatoes PDF
Rapid canopy dry down following chemical desiccation is critical to timely harvesting of potatoes. This project evaluated how several important varieties of potatoes respond to chemical desiccation.

Impact of low dosage foliar applied 2,4-D on skin color of red potatoes PDF
Foliar application of the herbicide 2,4-D has been reported to enhance the red color and improve skin appearance in red-type potatoes (Norland, Pontiac etc). This trial examined potential to use 2,4-D to enhance skin color of Norland grown in Saskatchewan.

Agronomy of New Potato Lines
2010 Growing Season

(Supported by the Agricultural Development Fund of Saskatchewan Agriculture and Food)

The objective of this on-going project is to evaluate the performance of a promising new potato cultivars under Saskatchewan growing conditions. Yields and quality as a function of N-fertility, crop maturity, irrigation, and in-row spacing have been evaluated in trials (2005-2010) conducted on the Plant Sciences Department Potato Research plots in Saskatoon. The site features a sandy loam, pH 7.8, EC < l dS, with 4% O.M. In all trials, each treatment plot consisted of a single, 8-m long section of row. Unless otherwise specified, the row spacing was 1 m between rows, with 25 cm between plants within a row. Weed control was achieved by applying eptam + metribuzin prior to planting, followed by linuron applied at ground crack. The crop was hilled twice prior to ground crack. In the irrigated treatments, an overhead system was used whenever soil water potentials averaged over the effective root zone (0-30 cm) fell below -50 kPa. Unless otherwise specified, the trials were top-killed using diquat in mid-September (ca. 120 DAP) and machine harvested by early October using a Grimme harvester. Tubers were cured for 10 days at 15oC, then cooled to 4oC for longterm storage. The tubers were mechanically graded into size categories; small = < 44 mm diam., medium = 44 - 88 mm and oversize = > 88 mm diam. The boiling, baking, chipping and frying quality of the various lines were evaluated using standard methodologies.

Detailed results from trials conducted from 2005-2009 are available at: www.usask.ca/agriculture/plantsci/vegetable/potato/pagronomy.htm

New cultivars tested in 2010

Milva (exclusive to a SSPGA member) - a yellow fleshed oval table potato

Pacific Russet - (SSPGA/EPG exclusive) - red skinned, white fleshed table potato

Gem Star (SSPGA members as local agents) - a russet processing potato

O'Pearle (exclusive to a SSPGA member) - a yellow fleshed "Baby" type potato

Alpine Russet – SSPGA member as local production/marketing agent

Blazer - SSPGA members as local production/marketing agents

Modoc – SSPGA member as exclusive agent

The trials evaluated the new lines against established industry standard lines (Russet Norkotah, Russet Burbank, Shepody and Norland).

2010 Growing Season

Temperatures were below normal throughout the 2010 growing season. About 34 cm of rainfall was received from June 1 - Aug 31 of 2010 (normal = 17 cm). Due to the steady rain, the 2010 crop only needed to be irrigated twice in late July/early August (5 cm total). Cool, wet conditions through most of 2010 were near-ideal for the development and spread of Late Blight. Despite repeated applications of protectant fungicides, blight was observed in the plot area in early August. Repeated rain events over the next 2 weeks allowed rapid development and spread of the disease, despite an intensified spray program. The resulting early loss of the crop canopy would have reduced the yield potential of the more blight sensitive cultivars.

Time of Planting and Harvest Trials

This trial examined the impact on time of planting and harvest on yields and quality. The trials were planted in mid-May or early June and harvested in late August or mid-September. This combination of planting and harvest dates resulted in plots harvested at 80, 90, 105 and 120 days after planting. Each treatment was replicated four times.

Results

Red skinned cultivars - In trials conducted in 2008-2010 Norland appeared to have a slight yield advantage at the early harvests (80 and 90 DAP) while Peregrine produced higher yields at the later harvests (Fig. 1). Neither of the Dakota series reds tested in 2008 had yields that warranted further testing. In a single year of testing (2010) Modoc showed some promise with yields that were comparable to the industry standard reds. The yield potential of Modoc may have been compromised in 2010 as it appeared sensitive to defoliation by late blight.

Russets - Yields of the russet type lines tested in 2008 were comparable at all four sampling dates, while in 2009 and 2010 yields of Russet Burbank and GemStar tended to lag behind the other russet cultivars (Fig. 2). In warmer years, yields of these slow developing cultivars tend to catch up late in the season, but this did not occur in 2009 and 2010 - a reflection of the cool 2009 growing season and problems with blight limiting crop vigour late in the season in 2010. The SSPGA line Pacific Russet showed excellent early and total yields in 2010 – it out-yielded the industry standard table russet (Norkotah) at all harvest dates. The two new processing russet lines introduced for testing in 2010 – Alpine and Blazer both out-yielded the industry standard for processing russets (Burbank). Yields of Shepody actually decreased with increasing time in the field in 2010 – this reflects increasing cullage to late blight. Shepody is extremely sensitive to blight.

In all three years of testing there was a progressive increase in specific gravities of the Russet cultivars with increasing time in the field – this was expected as gravities increase with crop maturity (Fig. 3). Specific gravities for all of the russet cultivars tested in 2010 were lower than in previous years – this again reflects the poor growing season and early termination of crop development in 2010 by late blight. The industry standard R. Burbank had some of the lowest gravities in all three trials which confirms the difficulty of getting this long season cultivar to mature within the limited growing season available in SK. The only russet cultivar in the 2010 trial that had what could be considered "acceptable" gravities for a processing potato was the new cultivar Alpine.

Yellow fleshed cultivars – The yield profiles of Milva and O'Pearle were comparable in 2009 (Fig. 4). However in 2010 yields of Milva were superior to O'Pearle and all the other yellow fleshed lines tested at all harvest dates. Milva appears to be highly tolerant of late blight – which may explain why it's performance was superior to the other less blight tolerant yellow lines tested in 2010. The new cultivar Yukon Gem had quite high gravities by the final harvest in 2010 (data not shown) – this contributed to its excellent performance in processing trials.

Summary of Time of Planting and Harvest Trials

The results of the time of planting * harvest date studies indicate the importance of maximizing the duration of the effective growing season for growers in Saskatchewan wishing to maximize their yields. Yields of both the new and industry standard cultivars tested increased progressively with duration in the field through to 120 days. A 120 day season represents the effective maximum available to potato growers in Saskatchewan - as earlier plantings or later harvests run into excessive risk of frost damage. By contrast, some growers opt for a very short duration growing season - in the seed industry this is used to minimize the risk of virus infection, whereas in the table sector, growers may opt for an early harvest to catch a high value market opportunity or to keep the size of their tubers within the optimum range desired in the marketplace. The results clearly illustrate the magnitude of yield sacrifice associated with an early harvest. The relative amount of yield loss associated with an early harvest was greater for late maturing cultivars like Gem Star and Russet Burbank than for earlier cultivars like Shepody or Norland. This suggests that growers should use caution when growing slow maturing cultivars like Gem Star or Russet Burbank as a slow start to the season, an unusually cool summer or an early fall could severely depress yields. In all cases the increase in yields with time in the field was strictly a function on an increase in average tuber size, rather than any increase in tubers produced. As expected, the dry matter content (specific gravities) increased with duration in the field - reflecting increased physiological maturity. The increase in specific gravity with maturity is of only limited importance to the seed and table growers of Saskatchewan - but this information will be of use to growers in other areas wishing to use these newly developed cultivars for processing.

N-Fertility Trials

At present N fertility recommendations for potatoes in Saskatchewan range from 150 #/a (dryland) to 190 #/a (irrigated). The objective of this trial was to determine optimum N-fertility rates under irrigation for a range of new cultivars. The soil-N treatments (total of 50, 100, 150, 200 or 250 #N/a) were achieved by pre-plant broadcasting sufficient 46-0-0 to supplement the residual soil N (ca. 50-100 # N/a). The N-treatments were laid out in an incremental design with two replicates.

Results - The N-response of AC Peregrine (2008) was quite flat, which corresponds to the results seen in trials conducted in 2005, 2006 and 2007. The lowest level of soil-N tested in 2008 (100 # N/a) resulted in total yields for AC Peregrine within 6% of the highest yield observed (150 # N/a).

In 2005, yields of GemStar increased through to the highest soil-N level tested (250# N/a). In 2006 and 2007, the N response by GemStar was more limited, with the lowest rate of N applied (100 #/a) producing yields that were within 10% of the highest yields produced (200 #/a). In the 2008 and 2010 trials, the N response of GemStar was again relatively flat, although it appeared that at least 150#/a N was required for optimum yields. It is noteworthy that yields of GemStar in 2010 were very low – reflecting the combined effects of poor seed quality and early loss of the tops due to Late blight. The limited yield potential of the 2010 crop may have restricted the N fertility response. A very high rate of hollow was noted in the Gem Stars in previous trials but there was no apparent relationship between the N rate applied and the incidence of hollow heart. In the 2008 and 2010 trials there was little hollow heart in the GemStars, irrespective of the N-fertility levels.

In 2006 and 2007 yields of AC Pacific Russet had peaked when 150 # N/a was used. In the 2008 trial, the highest yields were seen with the highest rate of N applied (250 #/a), however the actual yield difference between the highest and lowest rates of N applied were relatively small.

Yields of the new russet cultivar Blazer were low in the 2010 trial and were not influenced by the N fertility treatment. Another new russet cultivar Alpine showed much higher yields that peaked at around 150 #/a of total N.

O'Pearle which is grown for the small potato market showed no N fertility response. It is noteworthy that the N fertility variable also had no impact on the tuber size distribution of O'Pearle. The yellow fleshed table cultivar Milva showed a slightly negative yield response to increasing soil N availability. Even at the lowest level of available soil N, Milva produced yields that were far higher than the other cultivars tested in 2010. Milva appeared to be highly resistant to late blight – which suggests that late blight sensitivity, rather than soil N availability, may have been the major determinant of yields of the cultivars involved in the 2010 fertility trials.

Conclusion - The N fertility responses of the new cultivars were;
a) quite similar to one another, b) inconsistent from year to year and c) quite limited - in that the lowest rate of N applied (100 #/a) typically produced yields that were within 10% of the highest yielding treatments.
The inconsistency of the N fertility responses from year to year is likely driven by differences in the relative suitability of the growing season for potato growth. In poor growing seasons (such as 2010) yield responses to fertility treatments may be small as the availability of N is not limiting growth. While supra-optimal rates of applied N seldom had any significant negative impact on yields they may have had a negative impact on crop quality. Heavy applications of N tended to delay crop maturity making harvest difficult and leading to a reduction in specific gravities. At present, the economics of potato production dictate that growers should strive to maximize yields, even if it involves the application of very high rates of N fertilizer. As the cost of N increases and/or concerns increase regarding the environmental impact of over-application of fertilizers, the data generated in this study suggest growers of potatoes in SK can cut their N applications substantially without a significant yield penalty - and this management decision may actually increase crop quality.

Spacing trial

The effect of in-row spacing was fairly consistent across the cultivars tested in 2010. As seen in previous years, the closest in-row spacing (15 cm) consistently resulted in the highest yields – with less obvious differences between yields at 23 and 30 cm in-row spacings (Fig. 5). There was a tendency for the average tuber size to decrease along with the in-row spacing – but the effect was not significant in most cases (Fig. 6). Loss of crop vigor due to late blight may have limited yield responses to the spacing variable in 2010.

Conclusion - The results clearly illustrate the responsiveness of potato to manipulation of plant populations. If the objective is to maximize yields, a close in row spacing is clearly desirable as long as reaching a certain minimum tuber size is not a significant issue. In seed production a close in-row spacing would produce high yields and a highly desirable small average tuber size distribution. The table and processing sectors are looking for a larger size profile - and therefore a slightly wider in-row spacing might be desirable - as long as it does not represent an excessive compromise in yield potential or processing quality. It is noteworthy that yields were increasing with plant population through to the closest spacing used ie; 6". This raises two questions;
a) Would the trend continue for an even closer spacing ? We suspect that the yield profile would tend to plateau - with the cost benefit ratio depending on the relative cost of seed versus the harvested crop. For cultivars like O'Pearle and Peregrine, the yield profile at 6" was already quite small. There is a substantial price penalty in table markets if the tuber size falls below "A" size (1 3/4" or 55 mm diam). If however, the tuber size falls all the way to a "Creamer" size (1" or 25 mm) these tubers command a price premium as "Baby" potatoes. O'Pearle is specifically targeted at this Creamer market. The fact that yields of Creamer sized potatoes for O'Pearle was still increasing as in-row spacing narrowed to 6" suggests that there may be advantages of even closer in-row spacing.
b) Would a commercial grower expect to see the same responses? The yields obtained in this trial were well in excess of those obtained in typical commercial fields in SK. This may reflect efforts to manage all inputs so as to minimize crop stress or competition for resources. These management practices would have allowed the crop to express its full yield potential - even when there were very large numbers of plant competing for resources. However, the cost and cost efficiency of this type of management regime was not considered. If a grower cannot or does not provide the same stress-free production environment, this will lead to competition between plants within the row - with a corresponding drop in yield potential. This loss of yields will be greatest in situations where a high plant population tends to exacerbate competition effects. Growers will need to tailor their plant populations to match their ability to manage the crop while also factoring in costs of production and anticipated yields and economic returns.

Review of the agronomic responses of the new cultivars tested in 2008-2010;

O'Pearle

The small but uniform tuber size profile of O'Pearle makes it well suited to the baby potato market. It appears to be earlier maturing with a smaller more manageable vine than the present industry standard (Alpha). O'Pearle produces a higher proportion of tubers meeting the size standard for "baby" potatoes (<35 mm diam). O'Pearle responded very favourably to close in-row spacings. Some concerns regarding O'Pearle are;
a) the results from 2009 suggest that O'Pearle is sensitive to drought stress. By comparison, the standard cultivar Alpha is quite drought tolerant.
b) O'Pearle appeared to be more sensitive to defoliation by late blight than the present standard Alpha.
c) O'Pearle showed a high percentage of tubers with common scab in the 2010 trial.

Milva

Milva is hoped to represent an alternative to Yukon Gold as a smooth skinned yellow fleshed table potato. Milva appeared to have exceptional yield potential, even in early harvests. Its tuber size distribution was more uniform than Yukon Gold and it also shows less tendency to oversize. Milva is exceptionally tolerant of Late Blight and also has fewer problems with scab than Yukon Gold. The only significant limitation of Milva may be that its tubers are tear-drop shaped - and this shape is not familiar in the North American marketplace.

Pacific Russet

Pacific Russet is an early maturing dark russet line designed for use in the table market. Once issues with limited supplies of quality seed were rectified, this SSPGA line performed very well. Pacific Russet is clearly superior to all other russet lines for yield potential, especially early in the season. While the average tuber size of Pacific Russet is quite large, tuber size can be manipulated by altering in-row spacings. Pacific Russet appears to be quite sensitive to both defoliation and tuber decay caused by late blight. Pacific Russet has limited processing potential.

GemStar

This recently released processing russet had performed well in trials conducted from 2005-2007, but it did not yield well in the trials conducted from 2008-2010. It appears that there may be issues with quality of the seed presently available for GemStar. Until these quality issues are rectified we cannot recommend the adoption of this cultivar.

Blazer and Alpine

Blazer and Alpine are newly released processing type russet potatoes. Both lines showed promise in the 2010 trials – consistently out-yielding the industry standard (Burbank). They also had superior processing quality than Burbank, especially during early harvests. Both of these lines also showed high levels of tolerance of late blight. More testing of these lines is warranted.

Modoc

This newly released red-skinned table cultivar showed some promise in the single season of testing in 2010. It produced yields that were comparable to the industry standard reds – despite early loss of the foliage to late blight. Modoc appears to have superior colour and appearance than Norland and is more scab tolerant than Peregrine.

Yukon Gem

This yellow flesh cultivar is envisioned as a replacement for Yukon Gold in the table market. Yukon Gem appears equivalent or superior to Yukon Gold in terms of yield potential, especially in years with significant late blight pressure. The processing quality of Yukon Gem was surprisingly good – it produced the highest quality fries of any line tested in 2010. Taste panels also indicated that the flavour of Yukon Gem was superior to Yukon Gold. Yukon Gem does not appear to be as sensitive to common scab as Yukon Gold. The only limitation to Yukon Gem may be its appearance – it does not have as uniform shape as Yukon Gold and it has pink eyes.

Agronomy of New Potato Lines
2009 Growing Season

(Supported by the Agricultural Development Fund of Saskatchewan Agriculture and Food)

Download PDF

Agronomy of New Potato Lines

(Supported by the Agricultural Development Fund of Saskatchewan Agriculture and Food)

The objective of these trials conducted from 2005-2009 is to evaluate the performance of a range of newly released potato cultivars under Saskatchewan growing conditions. Changes in yield and quality as a function of N-fertility, crop maturity, irrigation, and in-row spacing have been evaluated in trials conducted on the Plant Sciences Department Potato Research plots in Saskatoon. The site features a sandy loam, pH 7.8, EC < l dS, with 4% O.M. This site has only a limited history being cropped to potatoes - until 5 years ago it was in dryland alfalfa.

In all trials, each treatment plot consisted of a single, 8-m long section of row. Unless otherwise specified, the row spacing was 1 m between rows with 25 cm between plants within a row. Weed control was achieved by applying eptam + metribuzin prior to planting, followed by linuron applied at ground crack. The crop was hilled twice prior to ground crack. In the irrigated treatments, an overhead system was used whenever soil water potentials averaged over the effective root zone (0-30 cm) fell below -50 kPa. Unless otherwise specified, the trials were top-killed using diquat in mid-September (ca. 120 DAP) and machine harvested by early October using a Grimme harvester. Tubers were cured for 10 days at 15oC, then cooled to 4oC for longterm storage. The tubers were mechanically graded into size categories; small = < 44 mm diam., medium = 44 - 88 mm and oversize = > 88 mm diam. The boiling, baking, chipping and frying quality of the various lines were evaluated using standard methodologies.

Results from trial conducted from 2005 - 2008 trials are available at :
www.usask.ca/agriculture/plantsci/vegetable/potato/pagronomy.htm

New cultivars tested in 2009 trials

Milva (exclusive to a SSPGA member) - a yellow fleshed oval table potato
AC Peregrine Red (SSPGA exclusive) - red skinned, white fleshed table potato
Gem Star (SSPGA members as local agents) - a russet processing potato
O’Pearle (exclusive to a SSPGA member) - a yellow fleshed “Baby” type potato

The trials evaluated the new lines against established industry standard lines (Russet Norkotah, Russet Burbank, Shepody and Norland).

2009 Growing Season - temperatures in 2009 were well below normal from May through August but well above normal during the harvest period in September. While the cool temperatures would have delayed emergence and early growth, they should have been favorable during the crucial periods of tuber set and bulking. Unusually warm conditions in September facilitated top-kill and skin set but caused problems during storage. About 23 cm of rainfall was received from June 1 - Aug 31 of 2009 (normal = 17 cm). A total of 15 cm of supplemental irrigation was applied during the 2009 growing season. The 38 cm of total moisture received by the irrigated crop consistently maintained soil moisture levels above the -50 kPa stress threshold for potatoes. The combination of above normal rainfall and below normal temperatures reduced drought stress in the dryland trial. The dryland crop had adequate moisture through emergence and tuber set but experienced a moderate degree of stress through the early stages of tuber bulking.

Fig. 09-1. Soil water potentials, rainfall and irrigation events for the 2009 potato trials in Saskatoon.

Time of Planting and Harvest Trials

This trial examined the impact on time of planting and harvest on yields and quality. Irrigated trials were planted in mid-May or early June and harvested in late August or mid-September. This combination of planting and harvest dates resulted in plots harvested at 80, 90, 105 and 120 days after planting. In the dryland trial only a single combination of planting and harvest dates was used - the crop was planted in mid-May and harvested at 120 days after planting. In both the dryland and irrigated trials each treatment was replicated four times.

The early harvested plots had the tops removed by hand a week prior to the harvest. For the 120 day harvest, the plots were sprayed twice with Reglone 10 days prior to the harvest. The crop was machine harvested and then sized and graded as previously described.

Results

Yields in 2009 were substantially lower than in 2008. This likely reflects unfavorably cool conditions early in 2009. The cool growing season coupled with above average rainfall during the 2009 growing season allowed the production of unusually high yield s in the dryland trial (avg = 83% of irrigated).

Reds - In the irrigated trials conducted in both 2008 and 2009, total yields for Norland and Peregrine were comparable at all four growth intervals (Fig 09-2a). In the 2009 trial there had been relatively little difference in the specific gravities of Norland versus Peregrine at any of the havrest dates. This ran contrary to findings in previous years and in 2009, where Peregrine consistently had higher specific gravities than Norland (Fig 09-2b). Peregrine and Norland produced equivalent yields under the mild drought stress experienced in 2009 (Table 09-1). In years with more severe moisture deficits, Norland had tended to out-perform Peregrine. Specific gravities of both the red cultivars in the dryland trial were significantly lower than when the crop was irrigated. This ran contrary to previous finding, where gravities of the dryand crop tend to be equivalent or higher than an irrigated crop.

Figure 09-2a. Yields for various red-skinned potatoes under irrigation in 2008 and 2009.

Figure 09-2b. Specific gravities for various red-skinned potatoes under irrigation in 2008 and 2009.

Russets - Yields of the four russet type lines were very comparable at all four sampling dates in 2008. This is in contrast with the results in previous years and in 2009 where yields of Russet Burbank and GemStar tended to lag behind the other cultivars (Fig 09-3a). In warmer years, yields of these slow developing cultivars tend to catch up late in the season, but this did not occur in 2009 - again a reflection of the cool growing season. O'Pearle had the highest specific gravities at all harvest dates - this is typical of varieties with a European background. Milva appears to mature early , as indicated by both its yield profile and also the limited change in its specific gravities as the season progressed. Specific gravities for the late maturing processing varieties (Gemstar and Russet Burbank) were higher than expected given the relative lack of favorable growing conditions in 2009. In the dryland trial, Milva produced outstanding yields. The lowest yielding russet lines under irrigated conditions (Gemstar and Russet Norkotah) showed the smallest relative yield decline when grown without irrigation. Specific gravities for the Russet cultivars under dryland were generally comparable to the gravities under irrigation.

Figure 09-3a. Yields of russet-type potato cultivars under irrigation in 2008 and 2009.

Figure 09-3b. Specific gravities of russet-type potato cultivars under irrigation in 2008 and 2009.

Summary of Time of Planting and Harvest Trial

The results of the 2009 study, as well as previous similar studies reported previously, clearly indicate the importance of maximizing the duration of the effective growing season for growers in Saskatchewan wishing to maximize their yields. Yields of all of the new cultivars tested increased progressively with duration in the field through to 120 days. A 120 day season represents the effective maximum available to potato growers in Saskatchewan - as earlier planting or later harvest run into excessive risk of frost damage. By contrast, some growers opt for a very short duration growing season - in the seed industry this is used to minimize the risk of virus infection, whereas in the table sector, growers may opt for an early harvest to catch a high value market opportunity or to keep the size of their tubers within the optimum range desired in the marketplace. The results form this trial clearly illustrate the magnitude of yield sacrifice associated with an early harvest. The rate of yield gain was greatest for the earlier harvests but was still significant up to 120 days in the field. The relative amount of yield loss associated with an early harvest was greater for late maturing cultivars like Gem Star and Russet Burbank than for earlier cultivars like Milva or Norland. This suggests that growers should use caution when growing cultivars like Gem Star or Russet Burbank as a slow start to the season, an unusually cool summer or an early fall could severely depress yields. In all cases the increase in yields with time in the field was strictly a function on an increase in average tuber size, rather than any increase in tubers produced. Even at the latest harvest date (120 days) only small proportion of the tubers had exceeded optimum size for marketability (data not shown). It should however be noted that these trials were based on a relatively close (25 cm or 10") in-row spacing. Growers opting for wider in-row spacings may find a relatively large proportion of the crop grading out as oversize after 120 days - especially for cultivars like Norland, Milva, Shepody and Gem Star which have a larger than average tuber size profile. As expected, the dry matter content (specific gravities) increased with duration in the field - reflecting increased physiological maturity. The increase in specific gravity with maturity is of only limited importance to the seed and table growers of Saskatchewan - but this information will be of use to growers in other areas wishing to use these newly developed cultivars for processing,

Review of the new cultivars tested in 2009;

- the new "baby" potato cultivar O'Pearle actually produced the highest yields of any of the Russet types - suggesting that this cultivar has excellent potential for use in Saskatchewan - especially as the other "baby" type cultivars tend to be both late maturing and low yielding. The small but uniform tuber size profile of O'Pearle make it well suited to the baby potato market. The fact that this cultivar has an unusually high specific gravity also suggest that it may have superior storage potential. One concern may be the apparent sensitivity of O'Pearle to drought stress. We also noted a heightened degree of sensitivity to drought stress in a grower's field in 2009.

- Milva is hoped to represent an alternative to Yukon Gold or Shepody as a smooth skinned light russet table potato. Milva appeared to have excellent yield potential especially in early harvests. Its tuber size distribution was also far more uniform than Shepody and it shows far less tendency to oversize than either Shepody or Yukon Gold.

Table 09-1. Yield and quality components for Red and Russet potatoes under dryland conditions in 2009.

For each type of potato, values within columns followed by the same letter are not significantly different (p=0.05)

Agronomy of New Potato Lines
2008 Growing Season

(Supported by the Agricultural Development Fund of Saskatchewan Agriculture and Food)

Download PDF

Agronomy of New Potato Lines

(Supported by the Agricultural Development Fund of Saskatchewan Agriculture and Food)

The objective of these trials conducted from 2005-2008 is to evaluate the performance of a range of newly released potato cultivars under Saskatchewan growing conditions. Changes in yield and quality as a function of N-fertility, crop maturity, irrigation, and in-row spacing were evaluated in trials conducted on the Plant Sciences Department Potato Research plots in Saskatoon. The site features a sandy loam, pH 7.8, EC < l dS, with 4% O.M. This site has only a limited history being cropped to potatoes - until 5 years ago it was in dryland alfalfa.

In all trials, each treatment plot consisted of a single, 8-m long section of row. Unless otherwise specified, the row spacing was 1 m between rows with 25 cm between plants within a row. Weed control was achieved by applying metribuzin prior to planting, followed by linuron applied at ground crack. The crop was hilled twice prior to ground crack. In the irrigated treatments, an overhead system was used whenever soil water potentials averaged over the effective root zone (0-30 cm) fell below -50 kPa. Unless otherwise specified, the trials were top-killed using diquat in mid-September (ca. 120 DAP) and machine harvested by early October using a Grimme harvester. Tubers were cured for 10 days at 15oC, then cooled to 4oC for longterm storage. The tubers were mechanically graded into size categories; small = < 44 mm diam., medium = 44 - 88 mm and oversize = > 88 mm diam. The boiling, baking, chipping and frying quality of the various lines were evaluated using standard methodologies.

The results from the 2005 - 2007 trials are available at :
www.usask.ca/agriculture/plantsci/vegetable/potato/pagronomy.htm

2008 Growing Season

Temperatures in 2008 were well below normal in May and June, about normal in July and slightly above normal in August and through the harvest period in September. The frost free period (May 26 to Sept 24) was near the 30 year average. About 17 cm of rainfall was received from June 1 - Sept 1 (normal = 17 cm). Very limited precipitation throughout August resulted in exerted substantial moisture stress on the dryland crop during the crucial period of tuber set and bulking. A total of 15 cm of supplemental irrigation was applied during the 2008 growing season (Fig. 08-1).

Fig. 08-1. Soil water potentials, rainfall and irrigation events for the 2008 potato trials in Saskatoon.

N-Fertility Trials

The objective of this trial was to determine optimum N-fertility recommendations under irrigation for a range of new cultivars. The soil-N treatments (total of 100, 150, 200 or 250 # N/a) were achieved by pre-plant broadcasting sufficient 46-0-0 to supplement the residual soil N (ca. 100 # N/a). The N-treatments were laid out in an incremental design.

Results

The yield responses of the AC Peregrine, Gem Star and AC Pacific Russet to total soil-N levels ranging from 100-250 # N/a are presented in Fig 08-2.

Fig. 08-2. Yield responses of new potato cultivars to increasing levels of soil-N.

The N-response of AC Peregrine was quite flat, which corresponds to the results seen in trials conducted in 2005 through 2007. The lowest level of soil-N tested in 2008 (100 # N/a) resulting in total yields within 6% of the highest yield observed (150 # N/a).

In 2005, yields of Gem Star increased through to the highest soil-N level tested (250# N/a). In 2006, 2007 and again in 2008, the N response by GemStar was more limited, with the lowest rate of N applied (100 #/a) producing yields that were within 10% of the highest yields obtained in the trial. A very high rate of hollow heart was noted in the Gem Stars in previous trials but there was no apparent relationship between the N rate applied and the incidence of hollow heart. In the 2008 trial there was little hollow heart in the GemStars, irrespective of the N-fertility levels.

In 2006 and 2007 yields of AC Pacific Russet peaked when 150 # N/a was used. In the 2008 trial, the highest yields were seen with the highest rate of N applied (250 #/a), however the actual yield difference between the highest and lowest rates of N applied were relatively small.

Specific gravities of all four cultivars in 2008 were lower than in previous trials. In the trials conducted from 2005-2007, specific gravities had declined as the fertility level increased. However, in the 2008 trial there was no consistent relationship between specific gravities and N fertility levels (Fig 08-3).

Conclusion

The N fertility responses of the three new cultivars were;
a) quite similar to one another,
b) less consistent from year to year
c) quite limited - in that the lowest rate of N applied (100 #/a) typically produced yields that were within 10% of the highest yielding treatments.

Supra-optimal rates of applied N seldom had any significant negative impact on yields but did tend to delay crop maturity as reflected by the lower specific gravities. Delayed crop maturity would also tend to make it more difficult to achieve vine desiccation prior to harvest.

At present, the economics of potato production dictate that growers should strive to maximize yields, even if it involves the application of very high rates of N fertilizer. As the cost of N increases and/or concerns increase regarding the environmental impact of over-application of fertilizers, it is clear that growers can cut their N applications substantially without a significant yield penalty.

Time of Planting and Harvest Trials

This trial examined the yields and quality of new potato cultivars harvested 80, 90, 105 and 120 days after planting. Separate plots were grown for each planting and harvest date. In a dryland trial only a 120 day harvest was used.

Results

Reds - In the irrigated trial, total yields for Norland and Peregrine were comparable at all four growth intervals and were consistently higher than the yields for either of the Dakota lines. (Fig. 08-4a). In previous trials, Peregrine had higher tuber specific gravities than the other red varieties tested - in the 2008 trial this difference was less pronounced (Fig. 08-4c). Norland had the largest average tuber size, while Peregrine had the greatest proportion of the total yield falling into the small size category. Yields in the dryland trial for reds averaged less than 40% of the irrigated trials (Table 08-1). Norland appeared to be the most drought tolerant of the red lines tested. Specific gravities in the dryland trial were comparable to the irrigated crop.

Russets - Yields of the four russet type lines were comparable at all four sampling dates (Fig 8-4a). This is in contrast to previous years where the table russets (Pacific Russet and Russet Norkotah) were consistently higher yielding early in the season than the processing types (GemStar and Burbank). As in previous years, Pacific Russet and Gem Star had a larger tuber size profile than the other lines (Fig 08-4b). Specific gravities at the early harvest dates were higher than in previous years, while at the later harvests the specific gravities were similar to previous trials (Fig 08-4c). Yields from the dryland russet trial ranged from 28-40% of irrigated - with the processing types (GemStar and Burbank) appearing to be more sensitive to drought stress than the table types (Pacific and Norkotah) (Table 08-1).

Table 08-1. Yield and quality components for Red and Russet potatoes under dryland conditions in 2008.

Values within columns followed by the same letter are not significantly different (p=0.05)

Summary of Time of Planting and Harvest Trial

The results of this 4 year study clearly indicate the importance of maximizing the duration of the effective growing season if growers in Saskatchewan wish to maximize yields. Yields of all of the new cultivars tested increased progressively with duration in the field through to 120 days. A 120 days season represents the effective maximum available to potato growers in Saskatchewan - as earlier plantings or later harvests run into excessive risk of frost damage. By contrast, some growers opt for a very short duration growing season - in the seed industry this is used to minimize the risk of virus infection, whereas in the table sector, growers may opt for an early harvest to catch a high value market opportunity or to keep the size of their tubers within the optimum range desired in the marketplace. The results clearly illustrate the magnitude of yield sacrifice associated with an early harvest. The rate of yield gain was greatest for the earlier harvests but was still significant up to 120 days in the field. The relative amount of yield loss associated with an early harvest was greater for late maturing cultivars like Gem Star and Russet Burbank than for cultivars like Pacific Russet or Norland. This suggests that growers should use caution when growing cultivars like Gem Star or Russet Burbank as a slow start to the season, an unusually cool summer or an early fall could severely depress yields. In all cases the increase in yields with time in the field was strictly a function of an increase in average tuber size, rather than any increase in tubers produced. Even at the latest harvest date (120 days) only a small proportion of the tubers had exceeded optimum size for the table market. It should however be noted that these trials were based on a relatively close (25 cm or 10") in-row spacing. Growers opting for wider in-row spacings may find a relatively large proportion of the crop grading out as oversize after 120 days - especially for cultivars like Norland, Gem Star and Pacific Russet which have a larger than average tuber size profile. As expected, the dry matter content (specific gravities) increased with duration in the field - reflecting increased physiological maturity. The increase in specific gravity with maturity is of only limited importance to the seed and table growers of Saskatchewan - but this information will be of use to growers in other areas wishing to use these newly developed cultivars for processing.

Figure 08-4. a-c. Yields (a), tuber size profile at the final harvest (b) and specific gravities (c) for various red and russet-skinned potatoes under irrigation in 2008.

Spacing trial

This trial evaluated the impact of in-row spacing on yields and tuber size distribution of AC Peregrine, Pacific Russet and Gem Star over the 2005-2008 cropping seasons. The trial was planted in mid-May using 6, 10 or 14" (15, 25 or 35 cm) in-row spacings. The crop was grown, harvested and graded as previously described.

Results

Although crops yields varied considerably from year to year, yields of all three cultivars increased as the in-row spacing decreased in all four years of testing (Fig. 08-5). The magnitude of this yield increase was easily sufficient to offset the additional cost of seed required for the closer in-row spacing. As expected, the average tuber size increased as the distance between plants increased (Fig. 08-6). The average tuber size of Peregrine Red was much smaller than the other varieties. The larger average tuber size of Gem Stars is well suited for the production of french fries. Tuber specific gravities showed a small but consistent tendency to increase as the in-row spacing decreased (Fig 08-7).

Fig 08-5. Influence of in-row spacing on yields of Pacific Russet, Gem Star and Peregrine Red.

Conclusion

The results from this trial clearly illustrate the responsiveness of potato to manipulation of plant populations. If the objective is to maximize yields, a close in-row spacing is clearly desirable as long as tuber size is not a significant issue. A close in-row spacing would obviously be desirable in seed production where high yields combined with a small average tuber size distribution would be ideal. The table and processing sectors are looking for a larger size profile - and therefore a slightly wider in-row spacing might be desirable - as long as it does not represent an excessive compromise in yield potential or processing quality. The small but consistent decline in tuber specific gravity with increasing in-row spacing may be a concern for the processing sector.

It is noteworthy that yields were increasing with plant population through to the closest spacing used ie; 6" This raises two questions;

a) would the trend continue for an even closer
spacing ?
We suspect that the yield profile would tend to plateau - with the cost benefit ratio depending on the relative cost of seed versus the harvested crop. For cultivars like Peregrine, the yield profile at 6" was already quite small. There is a substantial price penalty in table markets if the tuber size falls below “A” size (1 3/4" or 55 mm diam). If however, the tuber size falls all the way to a “Creamer” size (1" or 25 mm) these tubers may command a price premium as “Baby” potatoes.

b) would a commercial grower expect to see the same responses ?
The yields obtained in this trial were well in excess of those obtained in typical commercial fields in SK. This may reflect efforts to manage all inputs so as to minimize crop stress or competition for resources. These management practices would have allowed the crop to express its full yield potential - even when there were very large numbers of plant competing for resources. However, the cost and cost efficiency of this type of management regime was not considered. If a grower cannot or does not provide the same stress-free production environment, this will lead to competition between plants within the row - with a corresponding drop in yield potential. This loss of yields will be greatest in situations where a high plant population tends to exacerbate competition effects. Growers will need to tailor their plant populations to match their ability to manage the crop while also factoring in costs of production and anticipated yields and economic returns.

Agronomy of New Potato Lines
2007 Growing Season

(Supported by the Agricultural Development Fund of Saskatchewan Agriculture and Food)

Download PDF

The objective of this series of trials conducted from 2005-2007, was to evaluate the performance of a range of newly released potato cultivars under Saskatchewan growing conditions. Changes in yield and quality as a function of N-fertility, crop maturity, irrigation, and in-row spacing were evaluated in trials conducted on the Plant Sciences Department Potato Research plots in Saskatoon. The site features a sandy loam, pH 7.8, EC < l dS, with 4% O.M. This site has only a limited history being cropped to potatoes - until 5 years ago its was in dryland alfalfa.

In all trials, each treatment plot consisted of a single, 8-m long section of row. Unless otherwise specified, the row spacing was 1 m between rows with 25 cm between plants within a row. Weed control was achieved by applying metribuzin prior to planting, followed by linuron applied at ground crack. The crop was hilled twice prior to ground crack. In the irrigated treatments, an overhead system was used whenever soil water potentials averaged over the effective root zone (0-30 cm) fell below -50 kPa. Unless otherwise specified, the trials were top-killed using diquat in mid-September (ca. 120 DAP) and machine harvested in early October using a Grimme harvester. Tubers were cured for 10 days at 15oC, then cooled to 4oC for longterm storage. The tubers were mechanically graded into size categories; small = < 44 mm diam., medium = 44 - 88 mm and oversize = > 88 mm diam. The boiling, baking, chipping and frying quality of the various lines were evaluated using standard methodologies..

The results from 2005 and 2006 are available online at: www.usask.ca/agriculture/plantsci/vegetable/potato/pagronomy.htm

2007 Growing Season

Temperatures and rainfall in 2007 were about normal through May and June, exceptionally hot in July and then August was cooler than normal. A total of 25cm of rainfall was received over the growing period of June 1 - Sept. 1 (normal = 17 cm), but most of this precipitation came in the form of two very heavy storm events in mid-June and mid-August. A total of 15cm of supplemental irrigation was applied during the 2007 growing season (Fig. 07-1).

Fig. 07-1. Soil water potentials, rainfall and irrigation events for the 2007 potato trials in Saskatoon.

N-Fertility Trials

The objective of this trial was to determine optimum N-fertility recommendations under irrigation for a range of new cultivars. The soil-N treatments (total of 100, 150, 200 or 250 # N/a) were achieved by pre-plant broadcasting sufficient 46-0-0 to supplement the residual soil N (ca. 100 # N/a). The N-treatments were laid out in an incremental design. Each cultivar was planted in mid-May in two 8-m long rows within each N-level. The in-row spacing was 25 cm, with 1 m between rows. Each treatment was replicated twice.

Results
The yield responses of the AC Peregrine, Gem Star, Dakota Jewel and AC Pacific Russet to total soil-N levels ranging from 100-250 # N/a are presented in Fig 07-2.

Fig. 07-2. Yield responses of new potato cultivars to increasing levels of soil-N.

The N-response of AC Peregrine was quite flat - which corresponds to the results seen in both 2005 and 2006. The lowest level of soil-N tested (100 # N/a) resulting in total yields within 5% of the highest yield observed (200 # N/a). There appeared to be a slight tendency for the proportion of oversize tubers to increase at the higher N levels.

In 2005 yields of Gem Star increased through to the highest soil-N level tested (250# N/a). In 2006 and 2007 the N response by GemStar was more limited, with the lowest rate of N applied (100 #/a) producing yields that were within 10% of the highest yields produced (200 #/a). Very high levels of N again appeared to promote the development of oversize tubers. A very high rate of hollow was noted in the Gem Stars (ca 45%) but there was no apparent relationship between the N rate applied and the incidence of hollow heart.

Yields of AC Pacific Russet were low in 2005 due to problems with seed quality and herbicide damage. In 2006 and 2007 neither of these problems occurred and Pacific Russet produced excellent yields which peaked when 150 # N/a was used.

Specific gravities of the four cultivars were consistent with previous trials. As was seen in the 2005 trial, specific gravities declined as the N application rate increased in 2007.

(Fig. 07-3). This is a fairly common finding, especially if the higher raters of applied N delay crop maturity.

Conclusion

The N fertility responses of the three new cultivars were;
a) quite similar to one another,
b) less consistent from year to year
c) quite limited - in that the lowest rate of N applied (100 #/a) typically produced yields that were within 10% of the highest yielding treatments.

Supra-optimal rates of applied N seldom had any significant negative impact on yields but did tend to delay crop maturity as reflected by the lower specific gravities. Delayed crop maturity would also tend to make it more difficult to achieve vine desiccation prior to harvest.

At present, the economics of potato production dictate that growers should strive to maximize yields, even if it involves the application of very high rates of N fertilizer. As the cost of N increases and/or concerns increase regarding the environmental impact of over-application of fertilizers, it is clear that growers can cut their N applications substantially without a significant yield penalty

Time of Planting and Harvest Trials

This trial examined the impact on time of planting and harvest on yields and quality. Irrigated trials were planted on May 16 and June 7 and harvested August 21 or October 5. This resulted in plots harvested at 80, 90, 105 and 120 days after planting. Separate plots were grown for each planting and harvest date. In a dryland trial only a single combination of planting and harvest dates was used - the crop was planted in mid-May and harvested at 120 days after planting. In both the dryland and irrigated trials, each treatment plot consisted of a single, 8-m long section of row. Each treatment was replicated three times in a split plot design (main plot = planting date and sub-plot = planting date). The rows were spaced 1 m apart with 25 cm between plants within a row. The irrigated trials were watered whenever soil moisture potentials in the hills dropped below -50 kPa. Weed control was achieved through application of herbicides and cultivation as previously described.

The early harvested plots had the tops removed by hand a week prior to the harvest. For the 120 day harvest, the plots were sprayed twice with Reglone 10 days prior to the harvest. The crop was machine harvested and then sized and graded as previously described.

Results

Reds - In the irrigated trial, total yields for Norland and Peregrine were comparable at all four growth intervals and were consistently higher than the yields for either of the Dakota lines. (Fig. 07-4a). Dakota Jewel consistently had the lowest yields of the red lines tested. Tuber size was much larger for Norland than the other red lines tested (Fig. 07-4b), while Peregrine had the smallest tuber size profile. As seen in previous trials, Peregrine had higher tuber specific gravities than the other red varieties in this trial (Fig. 07-4d). Yields in the dryland trial were about 70% of the irrigated trial for most cultivars - except in Dakota Rose where dryland yields were almost 90% of irrigated. This suggests that either Dakota Rose has exceptional drought stress tolerance or that its yield potential under non-stressed conditions is limited. Relative yields of the four red-skinned varieties in the dryland trial were very comparable to their relative yields under irrigation. Specific gravities and average tuber sizes in the dryland trial were quite comparable to the irrigated crop.

Russets - The new SSPGA line Pacific Russet was consistently the highest yielding in the russet trial, followed by Russet Norkotah. Yields of the processing type lines (Russet Burbank and Gem Star) lagged well behind the lines most commonly used in the table market. Yields and specific gravities of Gem Star were again inferior to the standard Russet Burbank. (Fig. 07-5 a and d). Pacific Russet and Gem Star had a larger tuber size profile than the other lines (Fig 07-5c). Specific gravities were low and or inconsistently in this trial. Processing quality at 80 and 90 days was uniformly poor. At the later dates, Gem Star had excellent fry and chip colors, while the poorest colors were seen in Burbank which is considered the standard in the processing sector. Yields from the dryland russet trial ranged from as low as 56% of irrigated for Burbanks, through to 92% of irrigated for Gem Star (Table 07-1). Relative yields of the russet varieties in the dryland trial were again comparable to the corresponding trial under irrigation - except that Gem Star outyielded Burbank in the dryland trial. Specific gravities in the dryland and irrigated trials were comparable, as was the processing quality of the crop.

Table 07-1. Yield and quality components for Red and Russet potatoes under dryland conditions in 2007.

Values within columns followed by the same letter are not significantly different (p=0.05)

Summary of Time of Planting and Harvest Trial

The results of this 3 year study clearly indicate the importance of maximizing the duration of the effective growing season if growers in Saskatchewan wish to maximize yields. Yields of all of the new cultivars tested increased progressively with duration in the field through to 120 days. A 120 days season represents the effective maximum available to potato growers in Saskatchewan - as earlier planting or later harvest run into excessive risk of frost damage. By contract, some growers opt for a very short duration growing season - in the seed industry this is used to minimize the risk of virus infection, whereas in the table sector, growers may opt for an early harvest to catch a high value market opportunity or to keep the size of their tubers within the optimum range desired in the marketplace. The results clearly illustrate the magnitude of yield sacrifice associated with an early harvest. The rate of yield gain was greatest for the earlier harvests but was still significant after 120 days in the field. The relative amount of yield loss associated with an early harvest was greater for late maturing cultivars like Gem Star and Russet Burbank than for cultivars like Pacific Russet or Norland. This suggests that growers should use caution when growing cultivars like Gem Star or Russet Burbank as a slow start to the season, an unusually cool summer or an early fall could severely depress yields. In all cases the increase in yields with time in the field was strictly a function on an increase in average tuber size, rather than any increase in tubers produced. Even at the latest harvest date (120 days) only small proportion of the tubers had exceeded optimum size for marketability. It should however be noted that these trials were based on a 25 cm (10") in-row spacing. Growers opting for wider in-row spacings may find a relatively large proportion of the crop grading out as oversize after 120 days - especially for cultivars like Gem Star and Pacific Russet which have a larger than average tuber size profile. As expected, the dry matter content (specific gravities) increased with duration in the field - reflecting increased physiological maturity. The increase in specific gravity with maturity is of only limited importance to the seed and table growers of Saskatchewan - but this information will be of use to growers in other areas wishing to use these newly developed cultivars for processing.

Figure 07-4. a-d. Yields (a), average tuber weights (b), tuber size profile at the final harvest (c) and specific gravities (d) for various red-skinned potatoes under irrigation in 2007.

Figure 07-5. a-d. Yields (a), average tuber weights (b), tuber size profile at the final harvest (c) and specific gravities (d) for various russet-skinned potatoes under irrigation in 2007.

Spacing trial

This trial evaluated the impact of in-row spacing on yields and tuber size distribution of AC Peregrine, Pacific Russet and Gem Star over the 2005-2007 cropping seasons. The trial was planted in mid-May using 6, 10 or 14" (15, 25 or 35 cm) in-row spacings. Each treatment row was 8 m long with 1 m between rows. Each treatment was replicated four times in a randomized complete block design. The trial was irrigated and weeds were managed as previously described. The crop was top killed in the 2nd week of September and harvested in early October (120 days after planting). The crop was graded as previously described.

Results

Although crops yields varied considerably from year to year, yields of all three cultivars increased as the in-row spacing decreased in all three year (Fig. 07-6a). The magnitude of this yield increase was easily sufficient to offset the additional cost of seed required for the closer in-row spacing. As expected, the average tuber size increased as the distance between plants increased (Fig. 07-6b). The average tuber size of Peregrine Red was much smaller than the other varieties. The larger average tuber size of Gem Stars is well suited for the production of french fries.

Fig 07-6. Influence of in-row spacing on yields (a) and average tuber weights (b) of Pacific Russet, Gem Star and Peregrine Red.

Conclusion

The results form this trial clearly illustrate the responsiveness of potato to manipulation of plant populations. If the objective is to maximize yields, a close in row spacing is clearly desirable as long as tuber size is not a significant issue. A close in-row spacing would obviously be desirable in seed production where high yields combined with a small average tuber size distribution would be ideal. The table and processing sectors are looking for a larger size profile - and therefore a slightly wider in-row spacing might be desirable - as long as it does not represent an excessive compromise in yield potential.

It is noteworthy that yields were increasing with plant population through to the closest spacing used ie; 6" This raises two questions;

a) would the trend continue for an even closer spacing ?
We suspect that the yield profile would tend to plateau - with the cost benefit ratio depending on the relative cost of seed versus the harvested crop. For cultivars like Peregrine, the yield profile at 6" was already quite small. There is a substantial price penalty in table markets if the tuber size falls below “A” size (1 3/4" or 55 mm diam). If however, the tuber size falls all the way to a “Creamer” size (1" or 25 mm) these tubers command a price premium as “Baby” potatoes.

b) would a grower expect to see the same responses ?
Growing conditions in this trial were kept near ideal - with all inputs managed to minimize crop stress or competition for resources. These management practices would have allowed the crop to express its full yield potential - even when there were very large numbers of plant competing for resources. If a grower cannot provide the same stress-free production environment, this will lead to competition between plants within the row - with a corresponding drop in yield potential. This loss of yields will be greatest in situations where a high plant population tends to exacerbate competition effects. Growers will need to tailor their plant populations to match their ability to manage the crop.

Agronomy of New Potato Lines
2006 Growing Season

(Supported by the Agricultural Development Fund of Saskatchewan Agriculture and Food)

Download PDF

The objective of this trial was to evaluate the performance of a range of newly released potato cultivars under Saskatchewan growing conditions. Changes in yield and quality as a function of N-fertility, crop maturity, irrigation, in-row spacing and herbicide treatments were evaluated in trials conducted on the Plant Sciences Department Potato Research plots in Saskatoon. The site features a sandy loam, pH 7.8, EC < l dS, with 4% O.M. This site has only a limited history being cropped to potatoes - until 5 years ago it was in dryland alfalfa.

In all trials, each treatment plot consisted of a single, 8-m long section of row. Unless otherwise specified, the row spacing was 1m between rows with 25cm between plants within a row. Weed control was achieved by applying metribuzin prior to planting, followed by linuron applied at ground crack. The crop was hilled twice prior to ground crack. In the irrigated treatments, an overhead system was used whenever soil water potentials averaged over the effective root zone (0-30cm) fell below -50 kPa. Unless otherwise specified, the trials were top-killed using diquat in mid-September (ca. 120 DAP) and machine harvested in early October using a Grimme harvester. Tubers were cured for 10 days at 15°C, then cooled to 4°C for longterm storage. The tubers were mechanically graded into size categories; small = < 44 mm diam., medium = 44 - 88 mm diam. and oversize = > 88 mm diam. The boiling, baking, chipping and frying quality of the various lines were evaluated using standard methodologies..

The 2006 growing season was cool and wet during May and June but temperatures were well above normal in July, August and early September. 20cm cm of rainfall was received over the growing period of June 1 - Sept. 1 (normal = 17cm). A total of 15cm of supplemental irrigation was applied during the growing season (Fig. 06-1). Several heavy rain events occurred in mid-September after top kill - this precipitation had little impact on yields but delayed harvest operations. No problems with insects or diseases were observed in any of the trials conducted in 2006.

• 2006 Agronomy Contents
• Nitrogen Fertility Trials
• Time of Planting and Harvest Trials
• Spacing Trial
• Metribuzin Response

Fig. 06-1. Soil water potentials, rainfall and irrigation events for the 2006 potato trials in Saskatoon.

N-Fertility Trials

The objective of this trial was to determine optimum N-fertility recommendations under irrigation for a range of new cultivars. The soil-N treatments (total of 100, 150, 200 or 250 # N/a) were achieved by pre-plant broadcasting sufficient 46-0-0 to supplement the residual soil N (ca. 100 # N/a). The N-treatments were laid out in an incremental design. Each cultivar was planted in mid-May in two 8-m long rows within each N-level. The in-row spacing was 25cm, with 1m between rows. Each treatment was replicated twice.

Results

The yield responses of the AC Peregrine, Gem Star, Dakota Jewel and AC Pacific Russet to total soil-N levels ranging from 100-250 # N/a are presented in Fig 06-2. As in the 2005 trial, AC Peregrine again had the highest overall yields of the cultivars tested in 2006, followed by Pacific Russet, then Gem Star with Dakota Jewel producing the lowest yields.

Fig. 06-2. Yield responses of new potato cultivars to increasing levels of soil-N.

The N-response of AC Peregrine was quite flat in both 2005 and 2006, with the lowest level of soil-N tested (100 # N/a) resulting in total yields within 10% of the highest yield observed (150 # N/a). In 2005 yields of Gem Star increased through to the highest soil-N level tested (250# N/a). In 2006 Gem Star showed a much more limited yield response to increasing N - with the highest N application rate producing the lowest yields.

Yields of AC Pacific Russet were low in 2005 due to problems with seed quality and herbicide damage. In 2006 neither of these problems occurred and Pacific Russet produced excellent yields which peaked when 150 # N/a was used.

Specific gravities of the four cultivars were more erratic than seen in previous trials and there was no consistent relationship between N fertilizer rates and specific gravity.

Fig. 06-3). Influence of soil-N levels on specific gravities of new potato cultivars.

2006 Time of Planting and Harvest Trials

This trial examined the impact on time of planting and harvest on yields and quality. Irrigated trials were planted on May 16 and June 7 and harvested August 21 or October 5. This resulted in plots harvested at 80, 90, 105 and 120 days after planting. Separate plots were grown for each planting and harvest date. In a dryland trial only a single combination of planting and harvest dates was used - the crop was planted in mid-May and harvested at 120 days after planting. In both the dryland and irrigated trials, each treatment plot consisted of a single, 8-m long section of row. Each treatment was replicated three times in a split plot design (main plot = planting date and sub-plot = planting date). The rows were spaced 1m apart with 25cm between plants within a row. The irrigated trials were watered whenever soil moisture potentials in the hills dropped below -50 kPa. Weed control was achieved through application of herbicides and cultivation as previously described.

The early harvested plots had the tops removed by hand a week prior to the harvest. For the 120 day harvest, the plots were sprayed twice with Reglone 10 days prior to the harvest. The crop was machine harvested and then sized and graded as previously described.

Results

Table 06-1. Yield and quality components for Red and Russet potatoes under dryland conditions in 2006.

Values within columns followed by the same letter are not significantly different (p=0.05)

Reds

In the irrigated trial, total yields for Norland where higher than for the other red-skinned lines at the first harvest (80 days) (Fig. 06-4a), followed closely by AC Peregrine, with Dakota Jewel and CV89075-1 lagging well behind. By the second harvest, yields of AC Peregrine were equal to Norland and significantly greater than for Dakota Jewel and CV89075-1. This trend continued through the 105 and 120 day harvests. Tuber size was much larger for Norland than the other red lines tested (Fig. 06-4b). By the final harvest over 12% of the tubers of Norland were in the oversize category (Fig.06-4c). Few oversize tubers were produced by the other varieties, even after 120 days in the field. AC Peregrine had much higher tuber specific gravities than the other red varieties in this trial (Fig. 06-4d). Yields in the dryland trial were about 50% of the irrigated trial (Table 06-1). Relative yields of the four red-skinned varieties in the dryland trial were very comparable to the corresponding irrigated trial. Specific gravities in the dryland trial were higher than under irrigation.

Figure 06-4. a-d. Yields (a), average tuber weights (b), tuber size profile at the final harvest (c) and specific gravities (d) for various red-skinned potatoes under irrigation.

Russets

While yields of the red lines increased steadily with increasing time in the field, yields of the russet lines showed little increase between the 90 and 105 day harvests (Fig.06-5a). This was a period of exceptionally high temperatures which may have slowed tuber development. The new SSPGA line Pacific Russet and Russet Norkotah had comparable yields at the early harvests (80 and 90 days), but in the later harvests, yields of Pacific Russet were substantially greater than for Norkotah. Gem Star and Burbank yields lagged well behind Norkotah and Pacific Russet at the 80, 90 and 105 day harvests, but reached Norkotah yields by the 120 day harvest. Yields of Gem Star doubled between the 105 and 120 day harvests, suggesting that this cultivar is best suited to regions with a long/warm growing season. Yields and specific gravities of Gem Star were not as good as in previous years - and were never significantly better than the standard Russet Burbank. (Fig. 06-5 a and d). Russet Burbank tubers were smaller than the other cultivars at all harvest dates (Fig 06-5c). Specific gravities of Pacific Russet, GemStar and Burbank at the 120 harvest were dramatically higher than at earlier harvests (Fig. 06-5 d) - suggesting that these cultivars require a long season to reach physiological maturity. Yields from the dryland trial of the russets were about 50% of the irrigated trial. (Table 06-1). Relative yields of the russet varieties in the dryland trial were again comparable to the corresponding trial under irrigation - with yields of Gem Star and Burbank lagging well behind Norkotah and Pacific Russet 120 days after planting. This is in direct contrast with the results from the dryland trial conducted in 2005 (Table 05-1) - where Burbank and Gem Star out yielded Norkotah and Pacific Russet. Severity of the water deficit in the dryland trials was more extreme in 2006 than in 2005.

Figure 06-5. a-d Yields (a), average tuber weights (b), tuber size profile at the final harvest (c) and specific gravities (d) for various russet-skinned potatoes under irrigation.

2006 Spacing Trial

This trial evaluated the impact of in-row spacing on yields and tuber size distribution of AC Peregrine, Pacific Russet, Gem Star and Dakota Jewel. The trial was planted on May 18 using 6, 10 or 14" (15, 23 or 35cm) in-row spacings. Each treatment row was 8m long with 1m between rows. Each treatment was replicated four times in a randomized complete block design. The trial was irrigated and weeds were managed as previously described. The crop was top killed in the 2nd week of September and harvested by the 2nd week of October (120 days after planting). The crop was graded as previously described.

Results

Yields of all cultivars increased as the in-row spacing decreased in both years (Fig. 06-6a). This yield response to spacing was more pronounced for Gem Star than for AC Peregrine or Pacific Russet - likely reflecting the low tuber set characteristic of Gem Star. Average tuber size increased as the distance between plants increased, with the greatest response observed as the spacing changed from 10 to 14"between seed pieces (Fig. 06-6b). The average tuber size for Gem Star was much larger than for Pacific Russet, with AC Peregrine having the smallest average tuber-size.

Fig 06-6a. Influence of in-row spacing on yields of Pacific Russet, Gem Star and AC Peregrine.

Fig 06-6b. Influence of in-row spacing on average tuber weights of Pacific Russet, Gem Star and AC Peregrine.

2006 Metribuzin Responses

Post-emergence application of the herbicide metribuzin represents a useful weed control tool in potato production. However yields of some varieties like Shepody can be suppressed by post-emergence treatments and there are also concerns that the treatments may adversely affect skin color in red potatoes. This trial evaluated the yield and quality response of new SSPGA lines - AC Peregrine and Pacific Russet to post-emergence treatment with standard and 2X rates of post-emergence metribuzin.

The trial was conducted on the Plant Sciences Department Potato Research plots utilizing standard production practices for irrigated potatoes. Eptam (2.4kg ai/a) and metribuzin (150g ai/a) were applied prior to planting in mid-May. Norland was included in the trial as a metribuzin sensitive red skinned check variety. Each treatment variety combination was planted in an 8m long row, and all treatments were replicated twice. The crop was hilled at emergence. At 4 weeks after emergence, when the plants were about 30cm tall the post-emergence metribuzin treatments were applied utilizing a CO2 powered small plot sprayer. This represented an advanced stage of crop development for post-emergence treatment - and as such would be expected to increased any crop stress associated with the herbicide treatment. The metribuzin rates tested were the recommended rate of 150g ai/a plus a 2X treatment (300g ai/a). Weather conditions at the time of spraying were sunny and 24°C. The crop was evaluated at weekly intervals for visual symptoms of herbicide damage as well as for weed control The crop was chemically desiccated in early September and harvested in late September. The tubers were weighed and graded according to size: small = < 44 mm diam., medium = 44 - 88 mm diam. and oversize = > 88 mm diam..

Results

The pre-plant eptam/metribuzin treatment provided excellent weed control through until the time of the first hilling. By the time that the post-emergent herbicide treatment was applied, significant numbers of red-root pigweed and Russian thistle had emerged. These were effectively controlled by both rates of metribuzin. No further attempt was made to clean up the weeds in the control treatments or any escapes in the herbicide-treated rows. There were no visual indications of any herbicide damage to the foliage at any time in this trial. Post-emergent applications of metribuzin had no significant impact on total yields of AC Peregrine or Pacific Russet even when applied at 2X the recommended rate and at an advanced stage of crop development. Yields of the metribuzin sensitive check Norland were reduced at the 2X rate. The average tuber size for all varieties was slightly higher in the treatments that received the 2X metribuzin treatment. Impact of the metribuzin treatments on tuber color after storage has yet to be determined.

Agronomy of New Potato Lines
2005 Growing Season

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The objective of this trial was to evaluate the performance of a range of newly released potato cultivars under Saskatchewan growing conditions. Changes in yield and quality as a function of N-fertility, crop maturity, irrigation and in-row spacing were evaluated in trials conducted on the Plant Sciences Department Potato Research plots in Saskatoon. The site features a sandy loam, pH 7.8, EC < l dS, with 4% O.M. This is the first year this site has been cropped to potatoes - the previous year it was in dryland canola and prior to that it was in a long term alfalfa crop.

The 2005 growing season was cool and wet during May and June. Precipitation and temperatures were near normal in July and August. Crop establishment was slow but conditions were excellent during tuber set and bulking. 37 cm of rainfall was received over the growing season (normal = 20 cm). A total of 13 cm of supplemental irrigation was applied to the plots (Fig. 1). Yields were relatively high in both the dryland and irrigated trials. Weed control was achieved by applying metribuzin prior to planting, followed by linuron applied at ground crack. The crop was hilled twice prior to ground crack. The crop was overhead irrigated whenever soil water potentials averaged over the effective root zone (0-30 cm) fell below -50 kPa. Weather conditions delayed application of the herbicide linuron and some plants had emerged at the time of application. This resulted in some crop damage (yellowing/death of the emerged leaves) and resulted in ca. 5% mortality, particularly to the fast emerging cultivars. No significant problems with diseases or insects were observed. Unless otherwise specified, the trials were top-killed using diquat in mid-September (ca. 120 DAP) and machine harvested in early October. The crop was graded into size categories; small = < 44 mm diam., medium = 44 - 88 mm and oversize = > 88 mm diam.

• 2005 Agronomy Contents
• Nitrogen Fertility Trial
• Time of Planting and Harvest Trials
• Spacing Trial

Fig.1. Soil water potentials, rainfall and irrigation events for the 2005 potato trials in Saskatoon.

2005 N-Fertility Trials

The objective of this trial was to determine optimum N-fertility recommendations under irrigation for a range of new cultivars. The soil-N treatments (100, 150, 200 and 250 # N/a) were achieved by pre-plant broadcasting sufficient 46-0-0 to supplement the residual soil N (ca. 100 # N/a). The N-treatments were laid out in an incremental design. Each cultivar was planted in mid-May in two 8-m long rows within each N-level. The in-row spacing was 20 cm, with 1 m between rows.

Results

The yield responses of the AC Peregrine, Gem Star and AC Pacific Russet to total soil-N levels ranging from 100-250 # N/a are presented in Fig 2. The N-response of AC Peregrine was quite flat, with the lowest level of soil-N tested (100 # N/a) resulting in total yields within 15% of the highest observed at 150 # N/a. Total yields of Gem Star increased through to the highest soil-N level tested (250# N/a).

The increase in total yields of Gem Star with increasing soil-N was attributable to an increase in average tuber tested. Yields of AC Pacific Russet were low relative to the other cultivars. This may reflect a greater damage by the late application of linuron, as AC Pacific Russet emerges earlier than AC Peregrine or Gem Star. The AC Pacific Russet also had some seed-borne viral diseases which may have reduced its vigor and yield potential. Total yields of AC Pacific Russet increased through to the highest level of soil-N applied.

Specific gravities of the three cultivars were fairly typical of the values seen in previous trials. In each case, specific gravities declined with increasing levels of total soil-N (Fig. 3). The average tuber size of Gem Star was far larger than AC Peregrine or AC Pacifc Russet (Fig. 4) Increasing soil-N tended to increase the average tuber size of Gem Star to a greater extent than the other cultivars tested.

	Fig 2. Yield response of AC Peregrine, Gem Star and AC Pacific Russet to soil nitrogen levels (2005).

Fig 3. Influence of soil nitrogen levels on specific gravities of AC Peregrine, Gem Star, and Pacific Russet.	Fig 4. Influence of soil nitrogen levels on average tuber size of AC Peregrine, Gem Star, and Pacific Russet.

2005 Time of Planting and Harvest Trials

This trial examined the impact on time of planting and harvest on yields and quality. Irrigated trials were planted on May 13 and June 7 and harvested August 26 or September 30. This resulted in plots harvested at 80, 90, 105 and 120 days after planting. Separate plots were grown for each planting and harvest date. In a dryland trial only a single combination of planting and harvest dates was used - the crop was planted in mid-May and harvested at 120 days after planting. In both the dryland and irrigated trials, each treatment plot consisted of a single, 8-m long section of row. Each treatment was replicated three times in a split plot design (main plot = planting date and sub-plot = planting date). The rows were spaced 1 m apart with 20 cm between plants within a row. The irrigated trials were watered whenever soil moisture potentials in the hills dropped below -50 kPa. Weed control was achieved through application of herbicides and cultivation as previously described.

The early harvested plots had the tops removed by hand a week prior to the harvest. For the 120 day harvest, the plots were sprayed twice with Reglone 10 days prior to the harvest. The crop was machine harvested and then sized and graded as previously described.

Results

Table 1. Yield and quality components for Red and Russet potatoes under dryland conditions in 2005.

Values within columns followed by the same letter are not significantly different (p=0.05)

Reds

In the irrigated trial, total yields for Norland where higher than for the other red-skinned lines until the final harvest (120 days) at which time AC Peregrine and CV89023-2 had higher yields (Fig. 5a). Norland has a tendency to oversize - by the final harvest over 25% of the tubers of Norland were in the oversize category (Fig. 5c). By contrast, AC Peregrine and CV89023-2 have a smaller average tuber size - this can be disadvantageous in short cool seasons or early harvested crops but can result in fewer problems with oversize tubers at later harvest dates. Peregrine has much higher tuber specific gravities than the other red varieties in this trial (Fig. 5d). In the dryland trial, yields were about 70% of the irrigated trial (Table 1). Relative yields of the four red-skinned varieties in the dryland trial were very comparable to the corresponding trial under irrigation - with AC Peregrine and CV89023-2 again out yielding Norland at 120 days after planting. Specific gravities in the dryland trial were higher than under irrigation.

Figure 5a-d. Yields (a), average tuber weights (b), tuber size profile at the final harvest (c) and specific gravities (d) for various red-skinned potatoes under irrigation.

Russets

As noted in the other trials, the new SSPGA line Pacific Russet performed poorly in this trial. This may reflect problems with seed quality and/or herbicide damage to the emerging plants. Russet Norkotah gave the highets yields in the early harvests (80 and 90 days) but in the later harvests Gem Star and Burbank yields continued to climb while Norkotah appeared to plateau (Fig. 5a). Gem Star’s exceptional yield potential in a longer growing season had been noted previously. Gem Star also has higher specific gravities and a larger average tuber size than Burbank - characteristics that are desirable in a processing potato (Fig. 5 b, c and d). Yields from the dryland trial of the Russets were about 80% of the irrigated trial - with Gem Star on dryland producing 90% of the yields seen under irrigation (Table 1). Relative yields of the russet varieties in the dryland trial were very comparable to the corresponding trial under irrigation - with Gem Star and Burbank again out yielding the other lines at 120 days after planting. The AAFC line (VO865-1) appeared to have limited merit in any of the categories evaluated in either the irrigated or dryland trials trial.

Figure 6a-d. Yields (a), average tuber weights (b), tuber size profile at the final harvest (c) and specific gravities (d) for various russet-skinned potatoes under irrigation.

2005 Spacing trial

This trial evaluated the impact of in-row spacing on yields and tuber size distribution of AC Peregrine, Pacific Russet and Gem Star. The trial was planted on May 16 using 6, 10 or 14" (15, 23 or 35 cm) in-row spacings. Each treatment row was 8 m long with 1 m between rows. Each treatment was replicated four times in a randomized complete block design. The trial was irrigated and weeds were managed as previously described. The crop was top killed in the 2nd week of September and harvested in early October (120 days after planting). The crop was graded as previously described.

Results

Yields of all three cultivars increased as the in-row spacing decreased (Fig. 7a). This yield response to spacing was more pronounced for Gem Star than for AC Peregrine or Pacific Russet - likely reflecting the low tuber set characteristic of Gem Star. Average tuber size increased as the distance between plants increased, with the greatest response observed as the spacing changed from 10 to 14" between seed pieces (Fig. 7b). The average tuber size for Gem Star was much larger than for Pacific Russet, with AC Peregrine having the smallest average tuber-size.

Fig 7. Influence of in-row spacing on yields (a) and average tuber weights (b) of AC Peregrine, Pacific Russet and Gem Star.

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Agronomy of New Potato Lines
2004 Growing Season

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The objective of this trial was to evaluate the performance of a range of newly released potato cultivars under Saskatchewan growing conditions. Changes in yield and quality as a function of crop maturity and irrigation were evaluated in trials were conducted on the Plant Sciences Department Potato Research plots located in Saskatoon. The site features a sandy loam, pH 7.8, EC < l dS, with 4% O.M. This is the first year this site has been cropped to potatoes - the previous year it was in dryland canola and alfalfa prior to that.

The irrigated trials were planted on May 14 and May 28 and harvested August 16 or Sept 16. This resulted in plots harvested at 80, 90, 105 and 120 days after planting. Separate plots were grown for each planting and harvest date in the irrigated trial. In the dryland trial only a single combination of planting and harvest dates was used - the crop was harvested at 120 days after planting. In both the dryland and irrigated trials, each treatment plot consisted of a single, 8-m long section of row. Each treatment was replicated three times in a randomized complete block design. The rows were spaced 1 m apart with 25 cm between plants within a row. The irrigated plots were watered whenever soil moisture potentials in the hills dropped below -60 kPa. Weed control was achieved through application of herbicides and cultivation.

The early harvested plots had the tops removed by hand a week prior to the harvest. For the 120 day harvest, the plots were sprayed twice with Reglone 10 days prior to the harvest. The crop was machine harvested and then graded into size categories; small = < 44 mm diam., 44 < medium < 88 mm and oversize = > 88 mm diam.

Results

The 2004 growing season was unusually cool throughout. This slowed establishment of the crop but produced excellent conditions during tuber bulking. Consequently yields were relatively high in both the dryland and irrigated trials. 27 cm of rainfall was received over the growing season. A total of 30 cm of supplemental irrigation was applied to the plots. No significant problems with diseases or insects were observed.

Reds

In the irrigated trial, Norland clearly outyielded all other red-skinned lines at all harvest dates (Figure 1 a-d). The only problem with Norland is its tendency to oversize - this was becoming apparent by the third harvest. The yield difference between Norland and AC Peregrine in the irrigated trials was wider than in other years. This may reflect the relatively short and cool growing season experienced in 2004. AC Peregrine is relatively slow to develop and consequently does better in a long growing season. It is interesting to note that in the dryland trial, yields of AC Peregrine and Norland were very similar (Table 1). Both of these lines appear to be quite drought tolerant. Tuber set by AC Peregrine is far higher than Norland resulting in a much smaller average tuber size. In both the irrigated and dryland trials, the performance of the two AAFC lines was much poorer than in previous years. This may be a function of poor seed quality.

Russets

At the early harvest dates in the irrigated trial the new SSPGA line Pacific Russet produced substantially higher yields than the other lines tested (Figure 2 a-d). This new variety appears to size quickly - making it well suited to Saskatchewan’s relatively short growing season. By contrast, GemStar is slow to establish, but given a long enough growing period it appears to have excellent yield potential and acceptable processing characteristics under irrigation. In both the irrigated and dryland trials, GemStar appears to set relatively few tubers and the average tuber size was consequently large. This may be desirable for processors but may represent a challenge in seed production. In the dryland trial which was harvested at 120 days after planting, GemStar was the highest yielding line (Table 1). The AAFC line was not outstanding in any of the categories evaluated in either the irrigated or dryland trials trial.

Table 1. Yield and quality components for Red and Russet potatoes under dryland conditions in 2004.

Values within columns followed by the same letter are not significantly different (p=0.05)

Figure 1 a-d. Yields (a), average tuber weights (b), tuber size profile at the final harvest (c) and specific gravities for various red-skinned potatoes under irrigation.

Figure 2 a-d. Yields (a), average tuber weights (b), tuber size profile at the final harvest (c) and specific gravities for various russet-skinned potatoes under irrigation.

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Agronomics of New Potato Cultivars
2001 Growing Season

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This trial was designed to evaluate some of the basic agronomic characteristics and management parameters required for several newly released cultivars of interest to Saskatchewan’s potato industry.

The trials were conducted on the Plant Sciences Department Potato Research plots located in Saskatoon utilizing standard production practices for commercial potatoes. The crop was seeded in mid-May, in rows 1 m apart. Irrigated plots were watered once soil water potentials fell below -60kPa. Typically, 2.5 cm of water was applied at each irrigation event. The dryland plots relied solely on rainfall. Yields were evaluated at 90 and 120 days after planting. At both harvests, the crop was graded into size categories; small = < 44 mm diam., 44 < medium < 88 mm and oversize = > 88 mm diam. Table stock yields included the medium and oversize categories while the seed category included the pooled yield of small and medium size tubers.

New Cultivars tested

AC Peregrine Red - a newly released very dark red skinned variety under exclusive Canadian licence to the Saskatchewan Seed Potato Growers’ Association.

Cherry Red - this Colorado variety is exceptionally red and holds its colour well, but is late maturing.

Umatilla - a new release from the Idaho breeding program, this russet skinned potato is believed to have superior processing and disease resistance characteristics to Russet Burbank.

Gem Russet - a new release from the Oregon breeding program, this russet skinned potato is believed to have better yields and processing characteristics than Russet Burbank.

The 2001 growing season was excellent, providing supplemental irrigation was available. Less than 3" of rainfall was received over the growing season and the dryland plots were severely moisture stressed.

Norland was consistently higher yielding than either AC Peregrine Red or Cherry Red at both harvests in both the dryland and irrigated trials. The average tuber size of AC Peregrine was considerably smaller than Norland or Cherry Red. None of the new russet lines were as early, high yielding or uniform in appearance as Russet Norkotah. Neither of the new russet lines produced final yields or specific gravities better than Russet Burbank. Gem Russet produced relatively high numbers of small tubers.

Table 1. New red-skinned potato cultivar yields in 2001.

Table 2. Yields for new russet-skinned lines in 2001.

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Agronomics of New Potato Cultivars
2000 Growing Season

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This trial was designed to evaluate some of the basic agronomic characteristics and management parameters required by several newly released cultivars of interest to Saskatchewan’s potato industry.

The trials were conducted on the Plant Sciences Department Potato Research plots located in Saskatoon utilizing standard production practices for commercial potatoes. The crop was seeded in mid-May, in rows 1m apart. Irrigated plots were watered once soil water potentials rose above -60kPa. Typically, 2.5 cm of water was applied at each irrigation event. The dryland plots relied solely on rainfall. Yields were evaluated at 90 and 120 days after planting. At both harvests, the crop was graded into size categories; small = < 44 mm diam., 44 < medium < 88 mm and oversize = > 88 mm diam. Table stock yields included the medium and oversize categories while the seed category included the pooled yield of small and medium size tubers.

Cultivars tested;

AC Peregrine Red - a newly released very dark red skinned variety under exclusive Canadian licence to the Saskatchewan Seed Potato Growers’ Association.

Cherry Red - this Colorado variety is exceptionally red and holds its colour well, but is late maturing.

Umatilla - a new release from the Idaho breeding program, this russet skinned potato is believed to have superior processing and disease resistance characteristics to Russet Burbank.

Gem Russet - a new release from the Oregon breeding program, this russet skinned potato is believed to have better yields and processing characteristics than Russet Burbank.

Legend Russet - a new release from the Oregon breeding program, this russet skinned potato is believed to have better processing characteristics and table appeal than Russet Burbank.

The 2000 growing season was fairly typical in terms of temperature, number of frost free days and rainfall. Late season drought reduced the yields of the slow maturing types in the dryland trials.

Norland was consistently higher yielding than either AC Peregrine Red or Cherry Red at both harvests in both the dryland and irrigated trials. None of the new russet lines were as early, high yielding or uniform in appearance as Russet Norkotah. All of the new russet lines produced final yields better than or equal to Russet Burbank. Umatilla was particularly early and high yielding. Specific gravities of the new russet lines were often higher than Russet Burbank, indicating excellent processing ability but also suggesting the potential for problems with blackspot bruising. The average tuber size of Legend was considerably larger than the other new russet varieties.

Table 1. New red-skinned potato cultivar yields in 2000.

Table 2. Yields for new russet-skinned lines in 2000.

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Agronomics of New Potato Cultivars
1999 Growing Season

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This trial was designed to evaluate some of the basic agronomic characteristics and management parameters required for several newly released cultivars of interest to Saskatchewan’s potato industry.

The trials were conducted on the Plant Sciences Department Potato Research plots located in Saskatoon utilizing standard production practices for commercial potatoes. The crop was seeded in mid-May, in rows 1 m apart. Irrigated plots were watered once soil water potentials fell below -60kPa. Typically, 2.5 cm of water was applied at each irrigation event. The dryland plots relied solely on rainfall. Yields were evaluated at 90 and 120 days after planting. At both harvests, the crop was graded into size categories; small = < 44 mm diam., 44 < medium < 88 mm and oversize = > 88 mm diam. Table stock yields included the medium and oversize categories while the seed category included the pooled yield of small and medium size tubers.

New Cultivars tested;

ND2937-3 - a newly released very dark red skinned variety under exclusive Canadian licence to the Saskatchewan Seed Potato Growers’ Association.

Umatilla - a new release from the Idaho breeding program, this Russet skinned potato is believed to have superior processing and disease resistance characteristics.

Gem Russet - a new release from the Oregon breeding program, this Russet skinned potato is believed to have better yields and processing characteristics than Russet Burbank.

The 1999 growing season was cooler and wetter than normal from May through July. Little supplemental irrigation was required until mid-August. Frost killed the vines in early September, just prior to the 120 days harvest. Yields under irrigation only marginally exceed those for the dryland trials. For many of the cultivars, there was little increase in yields from the 90 through to the 120 day harvest. In the dryland trials, this could be attributed to late season moisture stress. The lack of yield increase with time in the irrigated trial was unexpected.

Norland was higher yielding than the new red variety ND2937-3, irrespective of harvest date or availability of moisture during the growing season. Both of the two new russet lines were higher yielding than Russet Burbank, but not as high yielding as Russet Norkotah. The average tuber size of both Umatilla and Gem Russet was small indicating excellent potential for seed growers. Specific gravities of Umatilla and Gem Russet were far higher than Russet Burbank, indicating excellent processing ability but also suggesting the potential for problems with blackspot bruising.

Table 1. New red-skinned potato cultivar yields in 1999.

Table 2. Yields for russet-skinned lines in 1999.

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Agronomics of New Red-Skinned Potato Cultivars
1999 Growing Season

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This trial was designed to evaluate some of the basic agronomic characteristics and management parameters required by several newly released red skinned cultivars of interest to Saskatchewan’s potato industry.

The trials were conducted on the Horticulture Science Department Potato Research plots located in Saskatoon utilizing standard production practices for commercial potatoes. The crop was seeded in mid-May, in rows 1m apart. Irrigated plots were watered once soil water potentials rose above -60kPa. Typically, 2.5 cm of water was applied at each irrigation event. The dryland plots relied solely on rainfall. Yields were evaluated at 90 and 120 days after planting. At both harvests, the crop was graded into size categories; small = < 44 mm diam., 44 < medium < 88 mm and oversize = > 88 mm diam. Table stock yields included the medium and oversize categories while the seed category included the pooled yield of small and medium size tubers.

Cultivars tested;

Norland - is the standard red skinned variety for the Canadian Prairies. It is early maturing with excellent yields of fairly uniform tubers, but its skin tends to fade during storage.

Cherry Red - this Colorado variety is exceptionally red and holds its color well. This variety may be too slow maturing for local growing conditions.

VO498-4 - is a new release from the potato breeding program at Agriculture Canada Lethbridge. This variety has produced excellent yields of very uniform tubers under irrigated conditions but had performed poorly under drought stress.

This trial evaluated the impact of seedpiece spacing on the yields and tuber size distribution of these red-skinned varieties under irrigated and dryland conditions. The spacings tested were 15, 25 and 35 cm (6, 10 and 14"). The 25 cm spacing would represent the norm for Norland under irrigation while a wider spacing would be more typical in dryland production.

Spring of 1999 was cool and wet which delayed crop emergence. Subsequent growing conditions were generally favorable for potato production. Rainfall from planting through July was well above normal. Little irrigation was required until August. Cool temperatures minimized the need for irrigation from September through until the end of the cropping season. Crop vigor was generally good in both the dryland and irrigated trials but more heat would have helped promote yields.

Cherry Red produced a small, upright canopy, while the canopy for VO498-4 more closely resembled that of Pontiac. While the Norland crop had senesced by early September, the Cherry Red and VO498-4 were still growing vigorously at the time of top kill in early September.

Due to the abundant rainfall through until August, yields under irrigation were only marginally higher than those under dryland conditions (Table 1). VO498-4 and Norland had very comparable yield profiles in both the dryland and irrigated trials. By comparison, yields of Cherry Red were consistently poor. The specific gravities (dry matter content) of Cherry Red were considerably different than the other two varieties which suggests that Cherry Red may have unique cooking and handling characteristics. Increasing the plant population by reducing the in-row spacing either increased or had no effect on yields but consistently reduced the average tuber size. At the closest in-row spacing, average tuber size was still large enough to meet table standards.

Table 1. Yields and tuber size distribution of three red skinned potato cultivars at 90 and 120 days after planting under irrigated and dryland conditions

*Linear (L) or Quadratic (Q) relationship between variable and in-row spacing (P=0.05).

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Agronomics of New Red-Skinned Potato Cultivars
1998 Growing Season

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This trial was designed to evaluate some of the basic agronomic characteristics and management parameters required by several newly released red skinned cultivars of interest to Saskatchewan’s potato industry.

The trials were conducted on the Horticulture Science Department Potato Research plots located in Saskatoon utilizing standard production practices for commercial potatoes. The crop was seeded in mid-May, in rows 90 cm apart. Irrigated plots were watered once soil water potentials rose above -60kPa. Typically, 2.5 cm of water was applied at each irrigation event. The dryland plots relied solely on rainfall. Yields were evaluated at 90 and 120 days after planting. At both harvests, the crop was graded into size categories; small = < 44 mm diam., 44 < medium < 88 mm and oversize = > 88 mm diam. Table stock yields included the medium and oversize categories while the seed category included the pooled yield of small and medium size tubers.

Cultivars tested;

Norland - is the standard red skinned variety for the Canadian Prairies. It is early maturing with excellent yields of fairly uniform tubers, but its skin tends to fade during storage.

NorDonna - is a newly released (North Dakota Program) very dark red skinned variety. NorDonna may be slow maturing and lack the yield potential of Norland.

Cherry Red - this Colorado variety is exceptionally red and holds its color well. Again, this variety may be too slow maturing for local growing conditions.

This trial evaluated the impact of seedpiece spacing on the yields and tuber size distribution of Norland, NorDonna and Cherry Red under irrigated and dryland conditions. The spacings tested were 15, 25 and 35 cm (6, 10 and 14"). The 25 cm spacing would represent the norm for Norland under irrigation while a wider spacing would be more typical in dryland production.

The 1998 growing season was exceptionally long, with excellent growing conditions throughout if supplemental irrigation was available for the crop. The dryland trials showing symptoms of drought stress from early July through to the final harvest. The crop canopy for NorDonna was more uniform than Norland but was slower to establish. While the Norland crop had senesced by early September, the NorDonna crop was still growing vigorously at the time of top kill in mid-September. Cherry Red was intermediate between the two other cultivars in terms of its growth habit. The Norland crop canopy in the dryland plots was substantially larger than for the other two cultivars - suggesting greater drought tolerance.

Yields under irrigation exceeded those on dryland by a factor three fold averaged over the three cultivars and two harvest dates (Table 1). Norland was the highest yielding cultivar, irrespective of harvest date or availability of moisture during the growing season. NorDonna performed poorly while Cherry Red was intermediate between Norland and NorDonna. Increasing the plant population by reducing the in-row spacing had little effect on yields when moisture was limiting. When moisture was abundant, yields progressively increased as the in-row spacing narrowed. At the closest in-row spacing, average tuber size was still large enough to meet table standards.

Table 1. New red-skinned potato cultivar yields for 1998.

*Linear (L) or Quadratic (Q) relationship between variable and in-row spacing (P=0.05).

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Changes in Vine Moisture Content and Yields Following Chemical Desiccation of Potatoes

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Rapid canopy dry down following chemical desiccation is critical to timely harvesting of potatoes. The rate at which the tops die down can be influenced by; the type, amount, method and time of application of the top killer, crop vigor at the time of top kill, the cultivar and the weather conditions after application of the top killer. Limited information is available as to the potential for yields to change during the die down period.

This project evaluated how several important varieties of potatoes respond to chemical desiccation. Trials were conducted in from 1998-2000 on the Department of Plant Sciences Potato Research plots located in Saskatoon. The crop was planted in mid-May. In all three years Ranger Russet, Russet Burbank and Russet Norkotah were tested, while in 1999 and 2000 Shepody was also evaluated. The crop was irrigated and standard pest management and fertility recommendations were followed. The desiccant Reglone (diquat) was applied in the first week of September at 1.0 l/a via a ground sprayer in 120 l/a of water. The plots were sprayed in the evening to maximize efficacy of the product. Seven days after the initial application of top killer, a second application was made (0.75 l/a in 120 l water). The crop was harvested at specific intervals after top-killing with a small plot harvester.

Timing of harvest;

• a) Fresh harvest (1st week of September) - this approximates the typical time of top kill for seed and table potatoes in Saskatchewan.
• b) Top-Kill + 10 days (3rd week of September) - 10-14 days after top killing represents the earliest growers can typically expect to harvest after top killing.
• c) Top-Kill + 20 days (1st week of October) - by this point, growers expect the crop should be ready to harvest. Any further delay increases the risk of frost damage.

One third of the plot was harvested at each interval. The plots for each harvest were 8 m long with four replicates of each treatment arranged in a randomized complete block design. Just prior to each harvest, three plants in each replicate for each cultivar were used to determine the moisture content of the vines.

Results

The rate at which the tops dried down was comparable in the three test years. The Russet Norkotah vines died back more quickly than the other cultivars - this was expected as Norkotahs are early maturing and produce a relatively small and weak plant canopy (Figure 1). Ranger Russet was the slowest to desiccated - this also corresponds with most growers experience with this cultivar. Growing conditions following application of the top killer had a significant impact on how much yields increased following desiccation. In 1998, growing conditions were excellent for several weeks after application of the top killer. Yields increased quite substantially (30%) during this period (Table 1). By contrast, conditions in 1999 and 2000 were less conducive to crop growth and there was very little change in yields following the initial application of top killer in these years. The four cultivars were very similar in terms of how much their yields changed following top killing.

Table 1. Potato yields after top kill.

Conclusions

The results confirm growers observations as to the relative easy of top kill of processing type potato varieties. Cool conditions after top kill slowed desiccation, but frost accelerated drying. Contrary to expectation, the degree of yield change following application of the top killer did not increase in situations where vine kill was slow. The warm conditions conducive to rapid top kill actually appear to promote tuber bulking after top kill. By contrast, cool conditions which slow top kill, may also slow translocation of assimilates into the tubers after top kill.

These results indicate that growers need to tailor their top killing strategy to the cultivar and the growing conditions both prior to and after application of the top killer.

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Impact of low dosage foliar applied 2,4-D on skin color of red potatoes

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Foliar application of the herbicide 2,4-D has been reported to enhance the red color and improve skin appearance in red-type potatoes (Norland, Pontiac etc). This management practice is extensive used in production areas of north-central United States where warm soil temperatures interfere with good color development. This trial examined potential to use 2,4-D to enhance skin color of Norland grown in Saskatchewan.

** 2,4-D is not licenced for application to potatoes in Canada. **

Trials were conducted at the Horticulture Science Department Potato Research Plots in Saskatoon from 1996-1998. The site features a sandy loam soil. Norland (regular clone) was tested in all years. Standard management practices for irrigated potatoes were employed. The spray was applied when the crop had just begun to set tubers. Low volatile 2,4-D ester was applied at either 28 g a.i./a (recommended rate) or 60 g a.i./a (2 X rate) in 80 l/ha of water. The time of application and spray concentrations are based on recommendations by the University of Minnesota. The plots were harvested and graded in early October. Skin color was evaluated for 50 randomly selected tubers from each replicate of each treatment. Samples were also evaluated following storage.

Results

In 1996 and 1997 there were no indications of phytotoxicity or any changes in canopy structure or leaf shape following application of the 2,4-D . In 1998, the classic fiddleheading symptoms associated with 2,4-D exposure were observed within one week of treatment. These symptoms could be detected for several weeks but they did not appear to slow crop growth.

Table 1. Yields and tuber size distribution for Norland potatoes treated with foliar applied 2,4-D in 1996-1998.

* % of crop falling into this size category.

Treatment of Norland potatoes with 2,4-D resulted in no significant changes in yields or tuber size distribution in the three test years (Table 1.) . In 1996, at harvest, some of the tubers coming from the 2,4 D treated rows were obviously darker, with a smoother, shinier skin than tubers from the control rows. However, this difference was not consistent. Skin color in 1997 was uniformly poor - we suspect because of the hot conditions prevailing through July and August. When tuber colors were re-evaluated following six months of storage (4oC and 80% R.H.), the 2,4-D treated tubers had significantly darker color. Skin color of the 1998 crop at harvest was better than in 1997. There was no significant effect of the 2,4-D treatment on skin color at harvest.

Conclusion

Improvement in the color of red potatoes would enhance marketability, particularly if the treatment helps hold the color through storage. In this trial, foliar application of low rates of 2,4-D produced little change in yields or skin color of Norland potatoes either at harvest or following storage. The lack of response may be related to improper time of application therefore multiple applications will be evaluated in 1999.

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