Potato Fertility Research
Fertility trial results are available in the Potato Agronomy section. Visit the Cultivar and Cultural Trials page for the newest information.
Rising input costs coupled with the continuing drive towards better stewardship of the environment has lead many growers to re-evaluate their fertility management programs. Trials conducted by the Vegetable Program evaluate the impact of differing fertility programs on yields, quality, economic returns and fertilizer use efficiency.
Calcium Nutrition of Potatoes
... Problems and Potential Solutions PDF
requirements and testing program for potatoes in Saskatchewan PDF
Effective fertility management is critical to profitable production of potatoes. The crop is highly responsive to N fertilizer, but N fertilizer use efficiency is low (Rourke 1985; Porter and Sisson 1991). Consequently, growers striving to meet the crop's N requirements frequently over-fertilize. Excessive application of nitrogen is uneconomical, environmentally unsound and potentially detrimental to the crop (Gardner and Jones 1975; Westermann and Kleinkopf 1985).
The objective of this project was to determine optimum N-fertility recommendations under irrigation for a range of potato cultivars of interest to growers in Saskatchewan. The trials were conducted from 1994 – 2010 on the University of Saskatchewan 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. Wherever possible, standard commercial production practices were utilized. The trials were established in mid-May using certified, cut seed. Each treatment plot consisted of a single, 8-m long section of row, with 1 m between rows and 23 cm between plants within a row. Weed control was achieved by applying EPTC + metribuzin prior to planting, followed by linuron applied at ground crack. The crop was hilled twice prior to ground crack. This combination of herbicides and tillage provided a good level of weed control. The crop was overhead irrigated whenever soil water potentials averaged over the effective root zone (0-30 cm) fell below -50 kPa. Insects and disease problems were managed as required. The trials were top-killed using diquat in early September (ca. 100 DAP) and machine harvested in late September (120 day growing season). Tubers were cured for 10 days at 15oC, graded and then cooled to 4oC for longterm storage. Specific gravities were determined using the weight in air/weight in water method of determination. A high specific gravity is indicative of processing potential, whereas low specific gravities indicate either an immature potato or a potato suited only for table use.
The soil-N treatments (total of 50, 100, 150, 200 or 250 kg/ha) were achieved by pre-plant broadcasting sufficient 46-0-0 to supplement the residual soil N (ca. 25-75 kg/ha). The N-treatments were laid out in an incremental design. Each treatment was replicated twice.
The N fertility responses of Alpha, AC Peregrine, Norland, Ranger, Russet Norkotah, Pacific Russet, Russet Burbank and Shepody have been tested over a minimum of 5 growing seasons. To allow for comparisons across years with varying growing conditions, the yields for each soil N level were expressed as a % of the highest yielding treatment in each year.
For most cultivars, the relationship between yield and N applied was quadratic, with yields increasing with initial increments of N applied and then declining once N levels increased beyond an optimal level. Similar N response patterns for potatoes have been reported previously (Waterer 1997), although in some cases or cultivars, yields plateaued rather than declining with increasingly high levels of N (Westermann and Kleinkopf 1985; Porter and Sisson 1991; Lewis and Love 1994). In many cases, the yields obtained with just residual soil N (50-75 kg/ha) were within 15% of the maximum obtained with supplemental N. Fertilizer use efficiency of potatoes is known to be low and limited yield responses to N fertilizer are common in both research trials and commercial situations (Johnson et al. 1995).
Kelling and Wolkowski (1991) found the N requirements of fast maturing determinant cultivars such as Russet Norkotah were substantially higher than indeterminant types like Russet Burbank and Alpha. They suggested that in early maturing cultivars, tuber set and development occurs at the expense of root development, resulting in a small root system with low nutrient recovery potential and correspondingly high N fertilizer requirements. In this study, we found that the optimum level of N for relatively fast maturing cultivars such as Russet Norkotah and Pacific Russet were substantially higher than for longer season cultivars like Ranger or Alpha. However the fast maturing cultivar Norland was also found to have a relatively low fertility requirement.
Specific Cultivar Responses
AC Peregrine Red - the yield response of AC Peregrine Red to pre-plant N was fairly strong. Insufficient N resulted in a substantial yield loss, with yields reaching a plateau at about 150 kg N/ha. Alpha – yields for Alpha peaked at only 100 kg N/ha and showed a strong drop off with excessive N fertility. High rates of N fertilizer resulted in rank canopy in alpha which would have reduced harvest efficiency.
Norland – the yield response of Norland to pre-plant applied N was relatively flat. Yields exceeding 90% of site maxima were achieved with as little as 50 kg N/ha. Over-application of N had little impact on Norland yields, however the tubers took on a "rough" appearance.
Pacific Russet - trials conducted in Alberta indicated very limited N fertilizer responses for this fast maturing russet, with maximum yields achieved at 100 kg N/ha. Trials in Saskatchewan showed a yield benefit of applying substantially higher rates of pre-plant N to Pacific Russet.
Ranger – pre-plant application of 100 - 150 kg N/ha resulted in consistent high yields. N applications above 150 kg/ha negatively affected yields - Ranger is notoriously vigorous and excessive N may delay maturity and exacerbate problems with top-killing.
Russet Burbank – this long-season indeterminent cultivar is difficult to grow within the relatively short growing season available in Saskatchewan. Russet Burbank is sensitive to unfavourable temperature or moisture conditions, leading to substantial year to year variation in yields and quality. This year to year variability in yield potential was reflected in the R. Burbank crop's response to N fertility – with differing yield responses in each year of testing. In years with favourable production conditions yields increased with N fertility to reach a peak at about 150 kg N/ha. If however, conditions were not favourable, yields were suppressed with each increment of applied N. The N fertilizer appeared to encourage the Burbank crop to stay vegetative which was highly detrimental to yields in cool wet years.
Russet Norkotah – yields of Norkotah increased substantially to plateau at 150 kg N/ha. Application of "excess" N did not appear to have any negative impact of yields, harvest management or appearance of the Norkotah crop.
Shepody – showed a strong response to pre-plant applied N, with both insufficient and excess N resulting in substantial yield losses. Yields of Shepody peaked at around 150 kg N/ha.
Although there was substantial variability in the specific gravities amongst the cultivars and across the years of testing there was a fairly consistent trend for gravities to decline as the amount of N fertilizer applied was increased. This would be expected if the N fertilizer was encouraging the crop to stay in a vegetative state. The relatively limited impact of N fertility on specific gravities would be of limited importance in table potatoes but may be of relevance to processors. 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, along with concerns regarding the environmental impact of heavy applications of N fertilizers, the data generated in this study suggest growers of potatoes in SK may be able to cut their N applications without an excessive yield penalty. The resulting gain in fertilizer use efficiency along with improved crop quality and/or enhanced ease of harvest management associated with reduced N application should be factored into this decision.
Curwen, D and Peterson, L.A. 1976. The effects of rate and time of supplemental nitrogen application on yield and quality of Russet Burbank potatoes. Amer. Potato J. 53:402-403. Gardner, B.R. and Jones, J.P. 1975. Petiole analysis and the nitrogen fertilization of Russet Burbank potatoes. Amer. Potato J. 52:195-200. Johnson, C.L., Tindall, T.A., Thornton, M. and Brooks, R.A. 1995. Petiole N03-N sufficiency curves in newly developed potato cultivars. Proceedings of the winter commodity schools - 1995. University of Idaho Cooperative Extension System. p.209-217. Kelling, K.A. and Wolkowski, R.P. 1991. Influence of potato variety on petiole nitrate N critical levels. Amer. Potato J. 68:620-621. (Abstract). Kleinkopf, G.E., Kleinschmidt, G.D. and Westermann, D.T. 1984. Tissue analysis. A guide to nitrogen fertilization for Russet Burbank potatoes. University of Idaho Current Information Series No. 743. Lewis, R.J. and Love, S.L. 1994. Potato genotypes differ in petiole nitrate-nitrogen concentrations over time. HortScience 29:175-197. Porter, G.A. and Sisson, J.A. 1991. Petiole nitrate content of Maine-grown Russet Burbank and Shepody potatoes in response to varying nitrogen rate. Amer. Potato J. 68:493-505. Porter, G.A. and Sisson, J.A. 1993. Yield, market quality and petiole nitrate concentration of non-irrigated Russet Burbank and Shepody potatoes in response to sidedressed nitrogen. Amer. Potato J. 70:101-116. Rourke, R.V. 1985. Soil solution levels of nitrate in a potato-buckwheat rotation. Amer. Potato J. 62:1-8. Waterer, D. 1997. Influence of irrigation, nitrogen and plant populations on tuber size distribution of seed potatoes. Can. J. Plant Sci.77:273-278. Westermann, D.T. and Kleinkopf, G.E. 1985. Nitrogen requirements of potatoes. Agron. J. 77:616-621.
Rising input costs coupled with increasing market demand for “safer” products has lead many growers to consider “organic” or other reduced input production systems. This trial evaluated the yield potential of potatoes grown without synthetic fertilizers or pesticides relative to standard high input production.
The trial was conducted on the University of Saskatchewan Potato Research plots. The trial area was part of a conventional cropping program and as such did not meet established standards for “organic” production. The previous barley crop had been sprayed to control weeds. The field was disked twice prior to planting. Heavy applications of manure in previous seasons had raised the fertility levels to close to the optimum for potatoes (110 #/a N, > 120 #/a P2O5 and > 1000 #/a K2O). No supplemental fertility was added to the “low input” regime, while 20 #/a of N, P2O5, and K2O were applied close to the seed in the standard regime. The trial was planted in mid-May utilizing Elite 3 seed of Norland and Russet Norkotah. As whole seed was used, no seed treatments were applied in either regime. The seed was planted at 23 cm in-row spacings with 1 m between rows. Each plot consisted of two 20 m long rows of each cultivar.
The plots were irrigated as needed. No insecticides were applied in either regime and there were no significant insect problems. The standard plot was treated with fungicide 4 times as a preventative measure for control of early and late blight. No late blight was observed in either regime, but early blight was prevalent in the “low input’ regime. The standard plots were topkilled by applying Diquat followed 10 days later with a flail. The “low input” plots were flailed. The crop was harvested in early October after the first killing frost and the crop was weighed and graded.
Emerge and stand establishment were equivalent in the two regimes. Weed pressure was heavy in the test area with extensive infestations of volunteer grain, and the weeds introduced in the manure. The chemical regime provided excellent weed control for the duration of the season. Initially the cultivation appeared to be adequately controlling the weeds in the “low input” regime. However flushes of volunteer grain and late season weeds following the second hilling operation were problematic. The extensive weed growth in the low input regime appeared to reduce the vigor of the Russet Norkotah crop more than Norland. Norland is renowned as a robust, early maturing cultivar well adapted to low input situations. The extensive weed growth in the “low input” regime made topkill and harvest difficult. Reliance on flails as a top-killing method resulted in relatively poor skin set in the low input regime.
Norland appeared well suited to low input production, while Russet Norkotah was clearly not suited. The key difference appeared to lie in resistance to weed competition. Norland emerges quickly to produce a robust sprawling canopy that effectively smothers weeds. Norland also completes its growth cycle quickly, which renders it less susceptible to late season competition by weeds for fertility and moisture. By contrast, Russet Norkotah produces a relatively small canopy and it is prone to nutrient deficiencies and requires careful management of fertility and pest control inputs. All these factors render it less suited to low input production. The additional cost of inputs in the standard regime (ca $ 220/a) are roughly offset by the additional yields obtained for Norland (2 tons/a @ $ 200/t). However, with Russet Norkotah, the standard regime resulted in far superior returns even with a hypothetical price premium for a “low input” product.
For more information contact Doug Waterer at the University of Saskatchewan
Adequate calcium (Ca) is a critical aspect of the mineral nutrition of potatoes. Calcium is involved in both the structure and function of all plant cell walls and membranes. Inadequate supplies of calcium cause growth abnormalities like internal brown spot and hollow heart. Adequate calcium nutrition can also improve skin color in red potatoes, while reducing problems with blackspot bruising and buckskinning. Abundant tissue calcium also increases the tubers’ resistance to attack by soft rot bacteria during storage and may improve the performance of seed potatoes.
The soil test recommendation for Ca for potato production is around 300 ppm (600 #/a) and most soils in Saskatchewan contain 2 or 3 times the critical level of Ca. Deficiencies can occur, especially on the sandy soils preferred in potato production. Growers are urged to have the Ca levels of their soils tested - especially when moving onto a new field. Problems with calcium deficiency may still arise in fields that appear to have abundant Ca. This reflects the nature of Saskatchewan soils as well as manner in which Ca is absorbed and subsequently allocated within the potato plant.
While Saskatchewan soils tend to be rich in Ca, they may also contain very high levels of potassium (K). This superabundance of K in the root zone may competitively interfere with Ca uptake.
Most Ca uptake occurs near the tips of newly formed roots - consequently, anything that interferes with development of new roots interferes with calcium uptake. Environmental stresses like heat, cold and drought slow development of new roots, thereby leading to calcium stress. However, the most common cause of reduced root growth is the rapid development of other tissues - as these rapidly growing tissues effectively out-compete the roots for the energy resources needed for growth. In potatoes, root development slows dramatically as the tubers begin to set and expand. This reflects the fact that at tuber set, the plant diverts the majority of its available energy resources to support development of the tubers (Fig. 1). This creates a calcium shortage - precisely at the time when the calcium is needed most in the developing tubers.
Even if calcium uptake is adequate, calcium deficiencies can arise in the tubers due to the pattern of allocation of calcium within the plant. Calcium movement within the plant is governed by water movement - tissues that use the most water due to evapo-transpiration accumulate the most calcium. The leaves and stems of potato contain about 5X as much calcium as the tubers (Fig.2). This reflects the fact that the leaves and stems lose far more water than the tubers, because the tubers are constantly surrounded by moist soil.
The natural uptake and allocation of calcium explains why calcium deficiencies can arise in situations where there is abundant Ca available in the soil. This also explains why it is difficult to develop fertility management strategies to treat this problem. Dr. Jiwan Palta of the University of Wisconsin has been researching methods to management calcium fertility problems in potatoes for over a decade. His finding can be summarized as follows;
1) supplying Ca to the main root system is largely ineffective as a means for enhancing Ca levels in the tuber. This reflects the fact that potato tubers do not rely on the main root system for their Ca needs. Instead, the tubers appear to absorb Ca from their immediate vicinity using a system of fine roots that grow at the junction between the tuber and the stolon or directly out of the tuber surface.
2) consequently, the key to alleviating problems with Ca deficiencies in the tubers is to increase the levels of soluble, plant available Ca in the immediate vicinity of the developing tuber. This Ca is available for absorption by the tuber root system.
3) because of 1) and 2) above, pre-plant broadcast applications of calcium fertilizers tend to improve Ca levels in the leaves and stems, but not the tubers. Pre-plant applications of Ca are therefore only effective in situations where a soil test indicates a general deficiency of soil calcium. Pre-plant banding may be more effective if the fertilizer is positioned so that it increases the soil Ca levels in the immediate vicinity of the developing tubers. Recommendations out of P.E.I. suggest the application of 20-50 # Ca/a as CaNO3 in bands below and to the side of the seedpiece.
4) Foliar applications of Ca do not alleviate problems with Ca shortages in the tubers. There is some limited evidence that foliar applications of Ca (0.5 to 1.0 #/a) beginning at flowering will improve the Ca status of the tops, thereby enhancing general crop health.
5) The most effective approach to improving Ca levels in the tubers appears to be the mid-season application of Ca via side-banding or more practically through the irrigation system. Treatments begin at tuber set (early flowering) and continue at 2 week intervals for the next 6-8 weeks (3-4 applications). The calcium must be in a water soluble form (ie; CaCl2 or CaNO3) so that it can move into the vicinity of the developing tubers. Side-banded granular fertilizers must be irrigated in. The total amount of Ca required is still a matter of debate. Palta doubled tuber Ca levels by applying a total of 160 # Ca/a split over 4 applications in a moderately Ca deficient sandy soil. This beneficial effect on in season application of Ca occurred even in fields that had more than 1000 ppm (2000 #/a) of available soil Ca. It should be noted that applying this amount of Ca as CaNO3 also delivers 125 # N/a, which may be wasteful or potentially problematic in areas with a short growing season. Less frequent or more diluted Ca treatments may be adequate in situations where less dramatic improvements in Ca nutrition are required. The prolem of excess N loading could be avoided by using CaCl2 as the fertilizer source, however liquid CaCl2 is not commonly available in Saskatchewan.
6) Although Ca fertilizer treatment only rarely alter yields, they may affect tuber size distribution. Palta found that heavy applications of Ca occasionally reduced tuber set, resulting in a larger than average tuber size distribution. Research at the University of Saskatchewan looking at pre-plant and split applications of Ca on Norland and AC Peregrine growing on a Ca rich soil found an increase in average tuber size in one of two cropping seasons.