A high frequency of winterkill makes winter wheat sown into conventionally tilled seedbeds an unacceptably high risk crop in most of western Canada. If winter wheat is to be consistently overwintered throughout the prairie region, fields must be covered with a protective blanket of snow to minimize crop damage during periods of severe winter stress.
Direct seeding into standing stubble from a previous crop (stubbling-in) has proven to be the most practical method of maintaining a uniform snow cover on winter wheat fields. Consequently, the availability and performance of direct seeding equipment has been one of the primary factors determining the rate of expansion of winter wheat acreage in western Canada.
The management package and equipment required for the successful production of stubbled-in winter wheat has been available for many years. However, most farmers have been reluctant to invest in seeding equipment solely for the production of winter wheat. Therefore, it is expected that the level of winter wheat production in western Canada will be closely linked to the success farmers have with direct seeded spring crops. This linkage means that seeding equipment should be selected carefully to ensure it provides the flexibility required to direct seed a wide variety of crops under a wide range of conditions.
- Direct-Seeding Systems
- Supporting images - I
- Selection of a Seeding System
- Crop Residue Management
- Residue Clearance:
Hoe-Type Drills,Disc Drills, Row Spacing
- Supporting images - II
- Seed Placement:
Drill Design, Furrow Cave-in, Opener, Design and Depth of Operation, Seed Delivery Velocity, Row Spacing, Operation Speed, Packer Design, Field Conditions
- Direct-Seeding Openers:
Disc Openers, Hoe Openers
- Fertilizer Placement:
- Power Requirements
- Stubbled-In Winter Wheat
The term "direct seeding" often means different things to different people. Much of this confusion can be credited to earlier inappropriate use of descriptive terminology and a wide range of opinions as to what constitutes the ideal direct seeding equipment.
The terms "zero-till" and "no-till" have been used to identify production systems where the crop is seeded into standing stubble without any preseeding tillage. However, both terms are misleading unless their use is limited to descriptions of systems that employ broadcast seeding methods. Tillage is an important aspect of most successful crop production systems, even those where tillage is restricted to the creation of narrow furrows or small holes in the soil to optimize the environment for seed germination (see Chapter 11 for further details on crop establishment). Consequently, the term "direct seeding" most accurately reflects the objectives of production systems in which the crop is seeded into standing stubble without preseeding tillage.
A need to differentiate between high- and low-soil disturbance direct-seeding methods has been recognized. Along with this distinction came the realization that direct seeding was not an entirely new crop production concept.
The primary objective of most direct-seeding systems has been to reduce the number of operations required to prepare a seedbed and plant the seed by combining tillage and seeding equipment into one unit. The tillage component of most of the early versions of direct-seeding implements could be removed or used directly for tillage operations other than seeding.
One-ways and discers, which combined seeding and tillage into a single operation, were commonly used for high-disturbance direct seeding in the 1950's. In the 1970's, air seeders expanded the high-disturbance direct-seeding options to include the cultivator equipped with sweeps. Air seeder hoppers, which could be filled quickly and easily and were simple to clean out, also provided the additional advantages of bulk handling of grain and fertilizer and made the transport of equipment between fields rapid and simple.
Heavy-duty "no-till" disc drills and high-clearance hoe drills provided farmers with the first low-disturbance direct seeding options. Air seeders equipped with narrow knives later expanded the selection of low-disturbance direct-seeding equipment available to farmers.
Winter wheat lead the way in providing farmers with experience in low-disturbance direct seeding in western Canada in the 1980's. The term "stubbling-in" was coined to emphasize the importance of using low-disturbance direct-seeding equipment to ensure that stubble remained standing to act as a snow trap in winter wheat production systems.
The early 1990's saw a large increase in the acreage of direct-seeded spring-sown crops. Improvements in the design of seeding equipment, lower cost more effective herbicides, a better understanding of the role of tillage in crop production systems, and increased emphasis on residue management were the key factors responsible for the success of this major shift to direct seeding.
"One-pass" direct seeding has been the most recent concept to capture the imagination of direct-seeding proponents. It has the objective of pushing the economic and management advantages of reducing the operations involved in crop production to the limit by combining as many tasks as possible with the seeding operation. Equipment has been designed that tills the soil, treats the seed, bands the crop's total fertilizer requirements, plants the seed, and applies herbicides in a single operation. However, past experience has demonstrated that simple, cost effective, flexible, easily reversible, adaptive designs also have advantages in the complex ever-changing business of agriculture. It remains to be seen whether or not one-pass direct seeding systems can successfully achieve an acceptable balance among the often conflicting priorities of the different tasks they attempt to combine with the seeding operation.
When we purchase direct-seeding equipment, we also select a crop production system. Consequently, it is important that farmers consider all of their equipment and crop production options and acquire an in-depth understanding of their direct seeding needs before making major adjustments to current production systems. The following list provides a few examples of the questions that should be considered when evaluating direct seeding equipment and systems:
- How much experience do you have with direct-seeding equipment and cropping systems?
- What value is to be placed on soil conservation and other environmental concerns?
- How many acres will be seeded each year?
- What are the opportunities for, and the comparative advantages of, purchasing, renting, custom hiring, and sharing of direct-seeding equipment?
- Are there any special management problems that should be considered, e.g., fields with a large number of stones or soils that are difficult to manage?
- What width of seeding implement is required?
- How will fertilizer be applied?
- What tractor size is required to pull the seeding equipment?
- What tractor sizes are presently available on the farm?
- What labor is available on the farm?
- When is the labor available?
- Does one-pass direct seeding offer an opportunity for more efficient use of labor?
- What changes will be made when the current line of farm equipment is replaced?
- What type of residue management system will be used?
- What type of straw chopping and straw and chaff spreading system will be on the combine?
- What stubble height must the seeding implement pass through?
- Is snow trapping an important objective in the residue management system?
- Will the seeding implement:
- penetrate the soil and provide proper seed placement?
- seed through the heaviest residue expected?
- perform satisfactorily when crop residues are damp and soil conditions are wet?
- accommodate residue build-up over years and changes in soil tilth?
- be capable of seeding into the residues of all crop types included in the rotation?
- be used for tillage and fertilizer placement that does not include the seeding operation?
- be used for high- or low-disturbance seeding, or are both options required?
- Remember, winter wheat requires standing stubble for a snow trap.
- What type of openers will be used?
- Will one type of opener fulfil all the seeding requirements?
- Will the openers perform satisfactorily under a wide range of soil types and physical conditions?
- How many ranks of openers are there and what is the frame clearance on the seeding equipment?
- What is the preferred row spacing?
- Will the wheel placement on the seeding implement affect the crop residue flow through the drill frame?
- Does the seeding implement have effective depth control?
- What type of packing system will be used?
- Does the packer wheel width and type complement the opener width and furrow shape?
- Will the packing system provide good seed to soil contact to promote rapid germination?
- Will the packing system work without excessive mud build-up under damp soil conditions?
- What type of seed delivery system will be used? If it is an air system, how is the seed and fertilizer delivery speed regulated?
- What volumes of seed and fertilizer can the distribution system handle?
- How accurate and reliable are the seed and fertilizer distribution systems?
- Will the seed distribution system accommodate a wide range of seed sizes without damaging the seed?
- Is the seed and fertilizer delivery system easily cleaned out?
- How manoeuvrable is the seeding equipment when it is operating in the field?
- Are critical components of the seeding equipment easily monitored from the tractor?
- How easily and quickly can equipment be transported from field to field?
- How complex is the direct-seeding equipment to operate?
- How much maintenance will the direct-seeding equipment require?
- How easily and quickly can adjustments and repairs be made to the direct-seeding equipment?
- Will repairs be readily available at a reasonable price?
- What is the expected resale value of the direct-seeding equipment?
- How will the direct-seeding system affect weed control programs?
- Can the direct-seeding system be easily adapted to include the option for more intensive tillage?
- Can the direct-seeding system be easily modified to accommodate changes in input costs or new crops?
- Is the direct-seeding system cost effective?
Effective crop residue (trash) management programs are a necessary component of all successful direct-seeding systems. A detailed discussion of crop residue management, with special emphasis on winter wheat production, is given in Chapter 5 .
Vertical (frame) clearance, number of ranks (rows) of openers, distance between ranks, row spacing, shank design, and packer and seeding implement wheel placement are the main factors that determine the ability of hoe-type drills to pass through crop residues. High residue clearance is usually associated with wide row spacing, high frame clearance, three or more widely separated ranks of openers, and wheel placement outside the seeding implement frame. However, there are a number of factors that place practical limits on each of these variables. The challenge is to find the right compromise that fulfils the basic equipment requirements of each direct-seeding system.
Equipment manufacturers have shown a preference for low-profile drills because they tend to be visually more appealing and require less elevation of seed and fertilizer during filling than drills with long shanks. However, reducing shank length places limitations on residue flow through the drill, especially when crop residues are damp. High-clearance hoe drills with shank lengths of 25 to 30 inches (64 to 76 cm) should provide the frame clearance necessary to accommodate the residue of most crops.
Space between shanks within a rank has a large influence on crop residue flow through hoe-type drills. The space between shanks within a rank is determined by both seed row spacing and number of ranks of openers. For example, shank spacing within ranks is the same (two feet) for 12 inch (30 cm) row spacing on a two-rank drill as it is for 6 inch (15 cm) row spacing on a four-rank drill. The distance between ranks of openers also influences the residue clearance of hoe-type drills. As a general guide, hoe-type drills with approximately 30 inches (76 cm) between shanks within a rank and about 20 inches (51 cm) between ranks should provide the necessary clearance to handle the residue of most crops without plugging.
The number of ranks of openers and the space between ranks determines the distance and angle that seed and fertilizer must flow to reach the front and back openers on the drill. In turn, the distance between the front and back openers influences the height at which seed and fertilizer hoppers (boxes) must be positioned when gravity is used to deliver the seed and fertilizer. Air seeders provide greater flexibility in equipment design because the location of the seed and fertilizer delivery system is not dependent on opener position.
Unlike hoe-type drills, where straw and chaff are moved to the side as the openers and shanks pass through, the openers on disc drills must cut through crop residue. Therefore, excessive crop residues create problems for disc drills by interfering with disc penetration into the soil and causing "hairpinning" (forcing of uncut straw or chaff into the opener furrow). When hairpinning occurs, the straw and chaff "pop-up" after the drill passes leaving the seed on the soil surface. Cutting coulters in front of the openers, residue manager or row cleaner attachments, down pressure on the discs, opener design, and sharpness of the discs all influence soil penetration and the ability of disc drills to cut through crop residues.
Disc drills cut through straw and anchored stubble does not usually cause plugging problems. Residue flow through disc drills is also better when there is less finely chopped straw spread loosely on the soil surface. Therefore, heavy crop stands should be cut higher at harvest leaving a taller stubble for seeding into with disc- compared to hoe-type drills.
As with hoe-type drills, wet, loose residues provide the greatest challenge to direct seeding with disc drills. Wet, loose residues have a tendency to pile up in front of discs causing the drill to plug. Damp, tough residues and soft, undisturbed surface mulches, such as those that occur in fields that have a long history of direct seeding, also aggravate hairpinning problems with disc drills.
In addition to providing improved residue clearance, drills with wide row spacing have fewer openers, shanks, trips, and seed distribution connections per foot of width than drills with narrow row spacing. Consequently, the initial investment and subsequent repair costs should be lower for seeding equipment with wide compared to narrow row spacing. Because drills with wide row spacing have fewer openers in the ground than those with narrow row spacing, tractor horsepower requirements per foot of drill should decrease as row spacing increases. Fewer openers per foot of drill also reduces the weight requirement for adequate soil penetration by disc drills.
While the initial investment, maintenance, and operating costs may be lower for drills with wide row spacing, many agronomic studies reported in the scientific literature have concluded that narrow row spacing produces higher grain yields than wide row spacing. However, there is a growing controversy over the effect of row spacing on grain yield of spring sown crops in western Canada. Recent research with spring crops appears to suggest that wide row spacing produces yields comparable to narrow row spacing and further studies are being conducted to clarify this issue. In contrast, the results of 21 winter wheat field trials conducted in Saskatchewan have shown a consistent 1.5 percent decrease in grain yield for every one inch (2.5 cm) increase in row spacing between 3.5 (9.0) and 24.0 inches (60 cm) (see Chapter 11). This means that a 10 bu/acre grain yield on 12 inch (30 cm) row spacing would be expected to increase to 10.9 bu/acre if row spacing was decreased to 6 inches (15 cm). However, a 60 bu/acre grain yield on 12 inch row spacing would be expected to increase to 65.4 bu/acre if row spacing was decreased to 6 inches. Consequently, narrow row spacing is expected to produce the largest increase in gross returns for winter wheat in high-yielding environments when soil nutrient deficiencies, cultivar selection, seeding rate, diseases, etc., do not limit yield potential.
High concentrations of seed-placed fertilizer can retard germination, damage young seedlings, and increase the risk of winterkill (see Chapter 11). Therefore, because fertilizer is distributed over more rows, higher per acre rates of seed-placed fertilizer can be used with narrow than wide row spacings. For example, changing from a 12 inch (30 cm) to a 6 inch (15 cm) row spacing allows for the doubling of seed-placed fertilizer rates without changing the fertilizer concentration in the seed row provided the opener design and the width of seed and fertilizer spread in the seed row remain the same.
Narrow row spacings mean more openers in the soil and greater soil disturbance, which may promote the germination of more weed seeds. However, narrow row spacings provide for better competition with weeds, especially early in the growing season before the crop canopy has closed. At the other end of the growing season, stubble from plants seeded at narrow row spacings provides better support for the windrows of crops that have been swathed.
The primary function of all types of seeding equipment is to place the seed in a soil environment that allows for rapid establishment of healthy, vigorous plants. Shallow seed placement with good seed-to-soil contact provides the best seedbed environment for most direct-seeded crops.
Seeding depth is of special concern with winter wheat because deep seed placement results in weak, spindly plants that are more susceptible to winter damage, compete poorly with weeds, and are later maturing and lower yielding. Slower plant emergence in cool soils means that the negative effects of seeding winter wheat too deep are more pronounced with late seeding dates.
Winter wheat must be direct seeded into the standing stubble from a previous crop to minimize the risk of winter damage in western Canada. Soil moisture demand of the previous crop usually creates a very dry seedbed and, because soil moisture rarely improves with depth under these circumstances, little is to be gained by seeding deep. In fact, the drier the soil, the shallower the winter wheat seed should be placed. This often means that a few seeds may be left uncovered in the seed row when the seedbed is dry.
When fall weather conditions are cool and evaporative demands are low, shallow placement in dry soil allows the seed to effectively capitalize on the moisture provided by subsequent light rainfalls that only wet the first few centimetres (less that one inch) at the soil surface. Seeding depth can be deeper if significant rainfall prior to seeding has recharged soil moisture. However, even when soil moisture is plentiful, there should still be less that one inch (2.5 cm) of packed soil covering the winter wheat seed (see Chapters 7 and 11).
Seed placement is influenced by:
- Drill Design
- Furrow Cave-in
- Opener Design and Depth of Operation
- Seed Delivery Velocity
- Row Spacing
- Operation Speed
- Packer Design
- Field Conditions
Drill design has a large influence on the accuracy and uniformity of seed placement. In order to achieve proper seed placement, drills used for direct seeding must be able to penetrate untilled, residue covered seedbeds to ensure that the seed furrow opener reaches the desired seeding depth. They must then be capable of following the contour of the land while maintaining uniform soil penetration and providing a consistent soil cover over the seed. In short, the ideal drill for direct seeding should be sturdy enough to withstand the stresses of seeding into a parking lot while maintaining a level of control that is delicate enough to place seed with surgical accuracy and precision regardless of residue conditions.
In the last 20 years, considerable time and money have been spent on efforts to convert the heavy duty cultivator into a seeding implement and the standard double disc press drill into a tillage implement so that seedbed preparation and seeding could be combined into a single operation. During this period we have also had to rediscover the importance of accurate, uniform seed placement for successful crop production.
The cutting ability and down pressure has to be much higher than that provided by the standard double disc press drill design before disc openers can successfully penetrate most untilled, residue-covered fields. Therefore, the standard double disc press drill usually cannot be successfully used for direct seeding.
Down pressure on disc openers depends on the weight of the drill and the method by which the springs and carrying wheels transfer that weight to the opener or cutting coulter. Most modern disc drills that have been designed for direct seeding are able to transfer sufficient weight to the discs to cut through residues, penetrate the soil, and keep the openers in firm contact with the soil.
The press wheels on the standard double disc drill were designed to carry the weight of the drill and pack the soil over the seed, not to control the depth of opener penetration. Depth of soil penetration by the standard double disc drill is primarily controlled by the firmness of the soil. Soil firmness can be quite variable in untilled fields and the increased down pressure required for disc opener penetration further compromises the depth control. Therefore, in order to achieve accurate, uniform seed placement, the effect of the downward force on seeding depth has been limited by the addition of gauge wheels or depth bands on most disc drills that have been designed for direct seeding.
Single disc openers often have gauge wheels attached directly alongside each opener; however, this arrangement can reduce trash clearance and increase the breakdown of fragile stubble. The gauge wheels of double and triple disc openers are normally linked to the back of each opener. In addition to controlling the depth of disc penetration, gauge wheels that follow behind the opener also close the furrow and act as press wheels to pack the soil around the seed.
Air delivery systems were attached to heavy duty (HD) cultivators to create the original air seeders. However, HD cultivators were not designed to operate at shallow tillage depths and their wide frames, rigid hitches, and limited number of wheels left much to be desired as far as depth control was concerned.
Frame characteristics and wheel positions have a large influence on the operation depth of furrow openers on hoe-type drills. As the distance between the wheels and the frame size increase, the trash clearance usually improves and the depth control becomes less accurate and uniform. The large, inflexible frames of the HD cultivators on the original air seeders did not follow the ground as well as the narrow high-clearance hoe-drill sections. Therefore, air-seeder cultivators have been designed with floating wings and front-to-back, side-to-side, and even diagonal-flexibility that allows each section of the frame to follow the ground independently of the neighbouring section. Castor wheels have been added to the front of the main frame of many air seeder designs so that floating or flexible hitches can be incorporated to reduce the distance between the wheels and improve the ground following ability of the cultivator.
Number of wheels on the cultivator and the tire area that is in contact with the soil play an important role in controlling the depth of seeding of air seeders. There must be a large enough number of tires of sufficient width to minimize tire sinkage into the soil. Wheels mounted on walking axles in the frame also help to maintain the uniformity of seeding depth by improving the ground-following ability of the cultivator.
Transport wheels support the frame and provide the depth control on HD cultivators. Consequently, wheel placement and the number of wheels on the cultivator have a large influence on the performance of air seeders. Monitoring devices have been added to some implements to indicate the position of the cultivator frame relative to the wheels on the soil surface. These indicators allow the operator to make on-the-go depth changes when there are extreme variations in field conditions. However, the depth control of individual openers is still dependent upon air seeder frame position relative to the soil surface and the ease that the openers penetrate the soil.
The addition of packing systems that followed behind the air seeder cultivator provide for soil firming around the seed and help to maintain uniformity of seeding depth. Attachment of packing wheels directly to the opener shank improves the row-following ability of the packing system and allows the packer wheels to be used as gauge wheels for more accurate control of seeding depth. The wheels on the air seeder are used for transport of the cultivator and determine the basic frame height for coarse seeding depth adjustment. Adjustment of the gauge wheels on each shank then allows the operator to "fine tune" seeding depth. Frame levelling adjustments have to be made at the same time as seeding depth adjustments to ensure all openers operate at a uniform depth.
In addition to their influence on depth of opener operation, wheel placement on the tillage implement of air seeders affect residue clearance. Transport wheels and gauge wheels that are located inside and under the frame of the tillage implement interfere with the residue flow of air-seeder cultivators. In an effort to improve residue clearance, frame carrying press wheels have been mounted at the rear of the seeding implement to create what has become known as an air drill . This change eliminates the transport and gauge wheels from inside the tillage implement frame and essentially converts the air-seeder cultivator into a hoe-drill -type-seeding implement. Therefore, an air drill is basically a hoe drill with an air system for the delivery of seed and fertilizer.
The ground-following capabilities of air and hoe drills are determined by the distance between the rear packer wheels and the front wheels, which are normally castor wheels. Seeding depth is usually compromised with this type of drill when the front-to-back frame distance is increased to improve residue clearance or when frame sections are increased in width.
Seeding depth refers to the amount of soil that remains above the seed in the opener furrow, not the distance from the seed to the undisturbed soil surface between the seed rows. The distance the seedling has to grow to reach the soil surface (true seeding depth) is often difficult to establish at the time of seeding. Subsequent furrow cave-in, especially if seeding is followed by heavy rains, will often result in the seed being buried deeper than indicated by measurements made immediately after seeding. True seeding depth, or seedling emergence distance, can only be accurately determined by digging up emerged seedlings and measuring the distance between the seed and the stem region where chlorophyll (green) first appears (See Figure 2, Chapter 12).
The amount of furrow cave-in that will occur after seeding is difficult to estimate at the time of seeding because of the unpredictable effect of subsequent rainfall. However, as a general rule, greatest furrow cave-in is associated with high soil disturbance seeding operations that leave deep, narrow furrows.
c)Opener Design and Depth of Operation
Furrow shape and level of soil disturbance affect the depth of soil placed over the seed at the time of seeding and the amount of furrow cave-in that occurs after seeding. Furrow shape and level of soil disturbance are both influenced by opener profile and the depth at which the opener operates in the soil.
Deep, narrow furrows and high levels of soil disturbance usually result in deeper initial seed placement and greater subsequent furrow cave-in than is associated with wide, shallow furrows and low soil disturbance. Therefore, disc openers and hoe openers that create narrow furrows and/or high soil disturbance openers should be adjusted to operate at shallow soil depths (furrow depth below the undisturbed soil surface, not depth of soil that covers the seed) to ensure shallow seed placement. In contrast, openers that create deep, wide furrows can be used to roll soil aside thereby permitting shallow seed placement at the bottom of a deep furrow. Deep furrow openers operated at low speeds and wide row spacing are sometimes used to "seed to moisture" when moist soil several inches below the soil surface provides a more favorable environment for germination than dry soil near the soil surface.
The accuracy and repeatability of seed placement is influenced by opener design and soil entry angle. Seed is not always placed at the bottom of the opener furrow, nor do openers always provide a uniform cover of soil over the seed. In fact, plant emergence distance or true seeding depth can vary by more than an inch (greater than 2.5 cm) for some opener designs.
Nonuniform seed placement often produces variable plant stands. When soil moisture is marginal, seeding depths determined from plant emergence distances may not accurately reflect the average seeding depth, but the depth at which the most favorable conditions existed for germination and rapid plant establishment. Consequently, the percentage of seeds that produced plants and the uniformity of plant emergence distance should be established when opener performance is being evaluated.
Opener performance, and therefore seeding depth, is influenced by soil texture and moisture. Disc openers tend to cause more soil disturbance to heavy-textured and wet soils. In contrast, hoe openers often cause more disturbance to dry, hard soils. Clay soils that stick to metal surfaces can also influence seeding depth by causing changes in the opener furrow shape and level of soil disturbance. Â
Seed and fertilizer bounce when they are dropped into the furrows created by soil openers. The speed at which the seed and fertilizer hit the soil influences the amount of bounce and affects seed and fertilizer placement in the furrow. "Bounce" has been of particular concern with air delivery systems, especially those that place seed and fertilizer in separate bands in the same row. Air velocities that are too high within the distribution lines can damage the seed of some crops and, if delivery speed is not reduced sufficiently before the soil is contacted, excessive bounce can result in poor seed and fertilizer placement.
When row spacing is narrow and opener soil disturbance is high, the rear furrow openers may throw soil into the furrows made by openers mounted at the front of the seeding implement causing seeding depth to vary from row to row. The degree the "soil spill" from adjacent furrows influences seeding depth will be a function of the distance the openers throw soil and seed row spacing. Consequently, any factor that influences soil disturbance during the seeding operation, e.g., opener design, the distance the opener is placed in the soil, operating speed, etc., will play a role in determining the minimum distance seed rows can be spaced before soil spill from adjacent furrows becomes a significant factor affecting the uniformity of seed placement.
Soil flow over and around the opener, furrow shape, the distance soil is thrown from the furrow, the depth of soil that falls over the seed, and the level of stubble breakdown are influenced by speed of operation.
Hoe drills usually perform most effectively at speeds between 3 and 5 mph (5 to 8 km/hr). Because disc openers normally cause less soil disturbance than hoe openers, speed of operation should have less of an influence on the performance of disc drills. Consequently, as long as the discs cut cleanly through residues, disc drills can generally be operated at higher speeds than hoe drills.
Changes in operating speed can cause significant changes in the depth of seed placement with hoe openers. Soil is thrown further to the side of hoe openers and less soil flows back into the furrow thereby reducing seeding depth when the operating speed of a hoe drill is increased. Greater soil disturbance at higher speeds also increases the likelihood that soil from the rear openers will be thrown into the furrows of the front openers resulting in uneven seeding depths.
There are a large number of different types of packer systems available on the market today. The advantages and disadvantages of these systems vary with individual circumstances. Therefore, it is important that all aspects of the direct seeding program are taken into consideration when packer systems are being evaluated.
The stubble of the previous crop must be left standing between the winter wheat seed rows to provide a snow trap during the winter. Consequently, packer systems that do not follow the seed row (random packer systems), such as crowfoot and coil packers, are not suitable for use in the direct seeding of winter wheat. The firm, untilled soil between the seed rows also carries the weight of random packers leaving the soil in the seed-opener furrows unpacked. In contrast, on-row packers can have a large influence on seeding depth and the soil environment that is provided for winter wheat plant establishment.
Unpacked, loose soil will dry very quickly in hot, dry, windy weather. Therefore, soil moisture loses from evaporation are reduced when the soil is packed. Packing also improves the soil environment for seed germination by ensuring good seed-to-soil contact and increasing the conductance of soil moisture to the seed.
Wheel size and shape determines the area of soil surface in contact with the packer. It is important that the packer wheel width and style match the seedrow opener width and furrow shape to ensure uniform packing. Small diameter, narrow wheels can be used to concentrate the weight of light packer units. However, the packer wheel must be wide enough to uniformly pack the entire width of seed row.
Packer wheels can assist in furrow closure by pushing soil into open furrows. They can also be used to reshape the furrow produced by the seedrow opener. When matched with opener shape, packers compress loose soil above the seed thereby reducing the seedling emergence distance or true seeding depth. When seed row width is narrow, V-shaped packer wheels may further decrease the depth of soil over the seed by pressing the soil into the wall rather than the bottom of the furrow.
Packers can be used as gauge wheels to regulate the depth at which furrow openers operate (note: the emphasis here is on opener depth, rather than depth of seed placement). However, in order to effectively gauge opener depth, the packer wheel must be wider than the opener furrow.
The ground-following ability of the seeding implement and the soil depth at which the opener operates are controlled directly by packer wheels that carry the rear of the frame on hoe-press and air drills. The depth at which the furrow opener operates can also be controlled independently of the drill frame by attaching the packer wheels directly to the opener assembly. However, packer wheels mounted at the rear of the seeding implement usually provide better residue clearance than those that are part of the opener assembly.
Wheel construction can affect packer performance. Scrapers are often required to remove heavy clay soil from steel packer wheels when conditions for seeding are wet. Rubber covered packer wheels or rubber tires that shed mud usually perform better than steel wheels in wet, heavy clay soils.
Tillage is used to prepare a uniform seedbed for planting in conventional crop production systems. The absence of preplanting tillage for seedbed preparation creates many new challenges that must be overcome before direct-seeding systems can be successfully adopted.
Forward planning, well designed seeding equipment, and operator experience are essential elements in successful direct-seeding systems. Efforts must be made to maintain a smooth soil surface on fields that are direct seeded for more than one year in a row. Rough, ridged soil surfaces with variable residue cover compromise the effectiveness of drill operation. Crop residues must be uniformly spread and drill openers must be able to penetrate the soil to place the seed at the correct depth and provide the optimum soil environment for germination and plant establishment. Differences in soil texture and soil moisture content can also cause significant variation in drill performance and the operator must be prepared to make the necessary drill adjustments to ensure proper seed placement.
Fall seeded crops like winter wheat have their own special seeding problems. Recently harvested fields are often very hard and dry making them difficult to penetrate, even with direct-seeding equipment. At the other extreme, the most opportune time to seed winter wheat during the busy fall season is when conditions are too wet to combine. Wet soil and tough, damp residues create some of the most difficult direct seeding challenges.
The main function of openers on a direct-seeding implement is to place seed in a soil environment that favors quick germination and rapid establishment of vigorous, competitive plants. Because there is no preseeding cultivation with direct seeding, the soil opener must perform all the tillage that is necessary to prepare a proper seedbed and position the seed at the optimum depth in the soil with good seed-to-soil contact.
Winter wheat often has to be seeded into stubble fields that have been depleted of moisture by the previous crop. Shallow seed placement in dry, hard seedbeds requires good opener penetration and depth control. While hoe openers normally have better soil penetration and more positive seed placement, they usually leave a wider furrow and cause more soil disturbance then disc openers. However, as long as sufficient stubble is left standing to provide a snow trap, soil disturbance is usually not a major concern with direct seeded winter wheat. In fact, when soil moisture conditions are favorable, soil disturbance may be a positive factor if it stimulates germination of summer annual weeds and volunteer crops that are subsequently killed by low winter temperatures.
Opener performance varies with soil moisture content and physical characteristics. Clay and gravel or rocky soils present the greatest direct seeding challenges. Clay does not scour well from metal surfaces when soils are wet and clay soils can be nearly impossible to penetrate when they are dry. Disc openers should be equipped with cleaners to assist in the removal of wet, sticky clay soils from the opener surface. Stones can damage openers, especially disc type openers; however, some farmers prefer disc drills for seeding into rocky soils because, unlike hoe drills, they do not pull stones to the surface. Light, sandy soils usually present the fewest direct seeding problems provided seeding depth can be accurately controlled.
The performance of openers changes with wear. Therefore, it is important to routinely check for excessive wear and to replace or repair badly worn or damaged openers. It is a good idea to have extra openers on hand to minimize down time for repairs during the busy seeding period. Openers that follow directly behind tractor and seeding equipment wheels usually experience the greatest wear. These openers should be checked regularly and appropriate adjustments and/or replacements should be made to ensure uniform soil penetration by all openers. Disc-type openers have more moving parts and, because they rely on down pressure for soil penetration, they are subjected to greater vertical stresses than hoe openers. The cutting edge is the part of all openers that suffers the most wear and physical punishment. Accurate, uniform seed placement requires that the cutting edges of all openers are kept sharp. Sharp cutting edges are easiest to maintain when openers are constructed from materials that have good resistance to wear.
The soil penetration that can be achieved with standard double disc openers is usually not adequate for direct seeding. The cutting action of a double disc opener can be improved by the addition of a leading coulter ( triple disc opener), a residue manager, or a row cleaner. Larger diameter coulters (greater than 15 inches or 38 cm), which are aligned to ensure accurate tracking by the following disc opener, provide greater rolling and cutting action thereby reducing "hairpinning" problems. The purpose of coulters is to penetrate the soil and cut through residues, not to till the soil; however, they do influence seeding depth. Coulters should be adjusted to operate shallower than the desired seed placement depth leaving the furrow opener to provide the tillage required to ensure proper seed placement and good seed-to-soil contact after the packer wheel passes over the seed row.
Development of openers with a leading (off-set) disc has reduced the hairpinning problems of double disc drills by providing a cutting action comparable to that of the triple disc drill. The leading disc of the off-set double disc cuts the residue and an angled trailing disc opens the furrow. When used for direct seeding, there is usually less soil disturbance with an off-set double disc than with a standard double disc opener.
Single disc openers require less down pressure for soil penetration and cause less soil disturbance than double disc openers. The angle at which the disc enters the soil determines the furrow characteristics and seed placement of single disc openers.
There are a large number and variety of hoe-type openers available for direct seeding. They range in size from high-soil disturbance cultivator sweeps to low-soil disturbance narrow knife openers. Hoe-opener shapes vary from those with wide, blunt faces and long frontal surface areas that force the soil to flow around the opener to narrow wedge- or beak-shaped points with replaceable tips that roll the soil up and off the opener as it moves forward. Several opener designs have wings that range in size from those found on cultivator sweeps to small fins. The wings function to reduce the vertical forces (weight) required to hold the opener in the soil and to decrease draft by lifting the soil up and away from the opener as it moves forward.
Opener width and the manner in which the soil moves over and around the opener have a large influence on level of soil disturbance and furrow shape. Hoe openers, especially narrow openers that increase in width where they attach to the shank, throw the soil a greater distance and leave a wider furrow when speed of operation and/or seeding depth is increased.
Soil properties and soil moisture content have a large and variable influence on the performance of hoe openers. Heavy clay soils usually provide the greatest challenges to opener design because they become sticky and plastic when wet and form impenetrable masses when dry. Opener fins or wings and deflector plates often interfere with surface scouring of heavy, wet clay soils and provide platforms for the buildup of mud. Soil that sticks to the surface of the opener changes the shape of the opener and increases resistance to soil flow around the opener. These changes can create higher draft forces, increase soil disturbance, and produce wider, more open furrows.
Fertilizer is the largest variable expense in stubbled-in winter wheat production. Consequently, fertilizer unit cost and efficiency of use are major concerns to the winter wheat grower (see Chapter 17).
Phosphorus imbalances reduce the ability of winter wheat to recover from sublethal winter damage. Large increases in grain yield and earlier maturity can also be expected when phosphorus deficiencies are corrected, especially in growing seasons with cool, damp spring weather.
Phosphorus is an immobile element that does not move in the soil. Therefore, phosphate fertilizers should be placed in the seedrow to provide the germinating seedlings with immediate access to an adequate supply of phosphorus so that the important "phosphate starter effect" can be fully captured.
Most stubble fields are deficient in available soil nitrogen and winter wheat responses to nitrogen (N) fertilization are usually very dramatic making N a highly profitable input. The large N demands of stubbled-in winter wheat also makes N fertilizer a major cost factor, often exceeding 50 percent of the variable input costs. Consequently, N fertilization has an important influence on both the income and expense columns of the winter wheat balance sheet and application mistakes can be very costly.
Ammonium nitrate (34-0-0) fertilizer broadcast immediately after the soil has thawed in the spring has provided the most reliable, predictable grain yield responses of all the options for N application that have been evaluated for stubbled-in winter wheat. Responses have not been as consistent when other dry and liquid forms of N fertilizer have been broadcast or dribbled on the soil surface.
In dryland farming, surface applied nitrogen fertilizers require rainfall for incorporation into the soil. Therefore, the earlier the N fertilizer is applied in the spring the greater the likelihood that sufficient rainfall will be received to move the N into the rooting zone in time to ensure that critical early season crop demands are satisfied. Early spring application onto cool soils is especially important in minimizing volatilization losses (losses as NH 3) from urea (46-0-0) based fertilizers that have been broadcast or dribbled on the soil surface.
Nitrogen fertilizer may be placed in the seedrow at the time of seeding. However, this method of N fertilizer application should be used with caution for winter wheat. Field trials have indicated that high concentrations of N fertilizer in the seedrow can reduce seedling number and size, especially when the soil is dry at seeding. The damage to seedlings is greater with seedplaced urea than ammonium nitrate. The risk of winter damage is also increased when N fertilizer is seedplaced.
The crop response to seedplaced-N fertilizer is dependent on N form, fertilizer rate, seedrow spacing, width of seedrow spread, soil texture and organic matter content, and seedbed soil moisture. Consequently, there is not a simple rule of thumb that can be used to determine the "safe" rate of seedplaced N fertilizer for winter wheat (see Chapter 17 for a more detailed discussion of seedplaced N). Placement of N fertilizer a minimum of one inch from the seed row will minimize seedling damage.
The unit cost ($/lb) of ammonium nitrate is usually higher than that of urea and anhydrous ammonia. Unfortunately, surface broadcast urea is subject to nitrogen losses as ammonia gas, especially if it is applied to warm, moist soils, and anhydrous ammonia is a gas when released at normal air pressure. Consequently, the farmer usually has to choose between cheaper more volatile nitrogen forms, which must be incorporated into the soil to achieve maximum N-use efficiency, and higher cost less volatile ammonium nitrate that does not require a tillage operation for soil incorporation.
Banding has been the most common tillage method employed to incorporate nitrogen fertilizers that are subject to volatilization losses. Much of the recent interest in direct seeding has focused on side-banding of N fertilizer so that the tillage required for seeding and fertilizing operations can be combined.
To be effective, side-banding openers must provide sufficient separation of the seed and fertilizer to avoid seedling damage. In addition to maintaining a continuous soil barrier between the seed and N-fertilizer bands, an effective side-banding opener must adequately seal the furrow to prevent ammonia gas from escaping into the atmosphere when anhydrous ammonia is applied as part of a one-pass operation. Anhydrous ammonia bands can be especially difficult to seal when soils are excessively wet or dry.
The role of fertilizer side-banding in stubbled-in winter wheat production systems is still widely debated. Primary concerns with side-banding have focused on potential N losses, amount of seedbed disturbance, quality of seed placement, and tractor horsepower requirements.
Nitrogen application at the time of winter wheat seeding increases the risk of N immobilization by soil micro-organisms, leaching, denitrification, and losses in spring runoff. It is generally accepted that losses of this nature can be minimized if fall N applications are delayed until after the soil temperatures drop below 10°C. However, afternoon soil temperatures usually do not fall below 10°C until more than a month after the optimum planting date for winter wheat in western Canada.
Seed placement must not be compromised by fertilizer placement. Openers designed to side-band fertilizer usually cause more soil disturbance than simple seedrow openers. Accurate winter wheat seed placement is more difficult to accomplish when openers create considerable soil disturbance and seeding is followed by a rain or other factors resulting in furrow cave-in. Soil moisture in stubble fields is also often limiting for germination and establishment of winter wheat. When soil moisture is poor, excessive tillage during the fertilizer side-banding operation may result in further moisture loss and crop establishment problems.
Shallow seed placement is a prerequisite to successful winter wheat production. Banding N fertilizer below and to the side of the seedrow involves a deeper tillage operation than is required for optimum seed placement. As a consequence, increased tractor horsepower is required when N fertilizer banding is included in one-pass direct-seeding systems.
Width of seeding implement, seeding depth, opener type, opener down-pressure, operating speed, packing forces, tire rolling resistance, air seeder fan operation, and soil conditions all affect the tractor size required to pull a seeding implement in the field. Seeding implement frame type also has an influence on tractor power requirements. Wide rigid frames, or frames that have been stretched out to facilitate residue clearance, can cause the seeding implement to dig in or ride out when the soil surface is uneven. Deeper operating depths, and hence larger tractor size, are required to ensure that the openers stay in the soil when the seeding implement has poor ground-following ability.
Variable soil conditions have been shown to cause a greater than 30 percent difference in draft of the same seeding implement in the same field. Large field-to-field variations amplify the within-field-differences in draft, especially when sandy loam and heavy clay soils are compared. Consequently, in order to accommodate high draft variability due to differences in soil characteristics, a larger tractor unit than is suggested by average draft values is required to provide the necessary power reserves for the seeding operation.
Tractor size estimates include an adjustment for tractive efficiency, which compensates for slippage and transmission losses, and a tractor load factor, which provides for power reserves. These adjustments usually assume a tractive efficiency factor of 80 percent in untilled soils and a tractor load factor of 80 percent of maximum PTO output under normal operating conditions.
The tractor size required to pull a seeding implement is determined by multiplying the operating speed by the draft force and dividing by a conversion constant. Therefore, the required tractor size is directly related to both speed of operation and draft. For practical purposes, speed and draft can be considered to have independent effects on power as draft only increases by about four percent for each 0.6 MPH (one km 1/h) increase in operating speed.
Figure 1. Â Relative tractor size required to pull A) a low draft opener at a soil depth of 0.5 inches (1.25 cm) compared to B) a high draft opener at a soil depth of 2.0 inches (5.0 cm). The operation speed of both tractors was 4.5 MPH (7.5 km 1/h). Soil texture was a heavy clay. Tractor B is 4.5 times larger than tractor A (from Collins and Fowler, 1996).
The tractor size required to pull well scoured openers through the soil increases between 15 and 20 percent for every 0.4 inches (one cm) increase in seeding depth. This means that if seeding depth is increased from 0.4 to 2.0 inches (1 to 5 cm), the tractor size required to pull the average direct seeding implement is essentially doubled. However, large differences can be expected in the performance of different openers operated at different depths in soils with different properties (Figure 1).
Opener design has a large influence on the tractor size required to pull a seeding implement. No-till disc drills usually pull the easiest because the very thin cross-section of the discs offer low resistance when they penetrate the soil. Blunt, wide hoe openers that do not lift the soil normally produce the highest draft among the hoe and knife openers; but, the relative performance of openers should not be considered a constant for the different soil characteristics encountered under field conditions. For example, narrow hoe openers with small fins that lift the soil up and away from the opener move through the soil easily as long as the opener remains mud free. However, opener fins (and deflection plates) often interfere with surface scouring of heavy, wet clay soils and provide platforms for the buildup of damp, sticky soil. Soil that sticks to the surface of the opener increases the resistance to soil flow around the opener and, under field conditions, poor scouring can significantly increase the tractor size required to pull a drill through the soil.
Differences in draft due to soil characteristics, speed, and opener design are smallest when seeding depths are less than one inch (2.5 cm). Side-banding openers that place fertilizer below the seed have higher draft than conventional seedrow openers because they increase the depth of tillage. If seeding depth could be maintained at 0.4 inches (one cm), it is theoretically possible that tractor power requirements for low draft conventional seedrow openers could be as low as 2 hp/ft of drill width. In contrast, openers that band fertilizer 1.6 inches (4 cm) below seed sown 0.4 inches (one cm) deep have tractor power requirements that are often greater than 6 hp/ft under average soil conditions. In fact, field experience with seeding winter wheat into dry, heavy clay soils indicates that some fertilizer banding openers create tractor power requirements in excess of 12.5 hp/ft of drill width. These observations emphasize the fact that draft forces and input costs should not be considered as constants in economic analyses, rental rate calculations, and equipment selection for direct-seeding systems.
In western Canada, the primary reason for direct seeding winter wheat has been to provide a standing stubble snow trap that will reduce the risk of winter damage to an acceptable level. Lower operating costs, better crop moisture utilization, improved wildlife habitat, and reduced erosion are bonuses that are only realized if the snow trap is adequate to successfully overwinter the crop. As a further condition, the winter wheat must be successfully established in the fall before any rewards can be harvested.
Low-disturbance direct-seeding is the key to successful winter wheat production in most of the Canadian prairies. The 1990's have seen an explosion in the interest in direct seeding that has fuelled a thriving equipment manufacturing industry. A single drill design has not satisfied the diverse needs of farmers and equipment manufacturers have responded by producing an almost infinite number of design combinations. For example, there are over 100 different opener designs from which to choose and each opener type can be combined with an ever increasing number of packer options. However, as equipment options continue to increase, it is important to note that field surveys have identified proper equipment adjustment and operation as two of the most important ingredients in successful winter wheat production formulas.
Shallow seed placement is critical to the successful production of stubbled-in winter wheat in western Canada. Deep seed placement delays emergence, results in weak spindly plants that are more susceptible to winter damage, delays crop maturity, and reduces yield potential. The large increase in draft associated with increased seeding depth and/or fertilizer side-banding further emphasizes the importance of shallow drill opener operation so that tractor power and fuel costs can be minimized in stubbled-in winter wheat production systems.