Tillage

The wide range of soil characteristics, residue levels and cultural practices across the Prairies likely corresponds to the evolution of tillage practices, implements, seeding systems and seed openers. Producers across Canada have increasingly abandoned tillage regimes in favour of zero till or conservation tillage practices, and equipment manufacturers have continually improved implements to address producer adaptations.

Important tips for best management

  • The wide range of soil characteristics, residue levels and cultural practices across the Prairies has caused a corresponding evolution of a wide range of tillage practices, implements, seeding systems and seed openers. The best system for any one farm is unique and is often based on personal preference, with consideration of soil type, environment, erosion potential, soil moisture and previous tillage practices and timing.
  • For planting, a seeding implement that consistently places canola at one to two centimetres deep, while cutting through residue and placing and packing the seed into soil with optimal contact with the soil and soil moisture is ideal.
  • The system used to achieve this goal and meet a grower’s expectation for fertilizer rates and placement, and for cost, is unique to each farmer.
  • Canola emergence is influenced by seedbed conditions, especially moisture one to two weeks prior to and one week after seeding. Optimal seedbed conditions are more important for canola than for cereals because the recommended seed depth of one to two centimetres is shallower than it is for wheat. An optimal seedbed will:
    • supply soil moisture for germination and seedling establishment
    • provide adequate warmth and aeration
    • have minimal physical resistance for the seedlings to successfully emerge
    • be relatively free of weeds and disease
    • provide resistance to erosion
  • The impact different types of tillage has on soil compaction is reported in Caver’s ‘Compaction impacts on canola establishment‘ project.

Conventional tillage

A 2012 survey found that 12 per cent of the 996 canola growers surveyed in Western Canada said they used conventional tillage 1. Conventional tillage can be used to:

  • incorporate residue that interferes with herbicide/fertilizer application or seed placement
  • control weeds that have germinated
  • incorporate soil-applied herbicides or fertilizers
  • create a fine soil structure in the zone of seed placement that balances water infiltration and storage, and allows for adequate air movement
  • provide a warm seedbed in early spring conditions
  • dry the seedbed

Excessive or untimely tillage can:

  • deplete seedbed moisture
  • degrade soil structure leading to crusting problems
  • contribute to soil compaction
  • create large lumps
  • decrease soil organic matter
  • increase soil erosion

Performing tillage results in increased fuel, machinery and labour costs compared to no-till cropping systems. Conventional tillage seeding systems should only use tillage required to achieve a reasonably level, uniform, well-packed, granular surface structure with a mix of granules in the one to five millimetres size. Small granules will provide good seed-to-soil contact for water absorption, while larger granules provide some wind erosion protection. Granules that are smaller than 0.84 millimetres are susceptible to wind erosion. Leaving sufficient crop residues on the soil surface will reduce wind and water erosion without interfering with seeding operations.

To achieve a good seedbed in conventional tillage systems, the following questions should be considered:

  • Is the tillage implement suitable for the soil and residue conditions?
  • Is the soil moisture adequate so as to not promote erosion, yet not so wet as to result in large clods?
  • Is the implement properly adjusted for depth, speed, harrowing or packing pressure, etc. to produce a uniformly smooth, firm seedbed for precise shallow seed placement?

Considerable experience is needed to select the most suitable implement, to properly adjust it for the optimal seed depth placement, and to begin tilling at the right soil moisture content (concentration) in order to achieve a granular seedbed rather than a powdery or lumpy one. Sandy soils are easily worked into a fine seedbed with minimal tillage. However, the workability of sandy soils leaves little margin for error. Overworked sandy soils quickly become very fine structured and susceptible to water and wind erosion.

In contrast, clay-textured (heavy) soils should not be tilled under wet conditions because large lumps or clods can develop, which prevent adequate seed-to-soil contact. Subsequent tillage to break up these lumps can pulverize the remaining soil and make the soil prone to crusting. Crusting of low organic matter clay soils (ex. Grey Wooded soil zone) is a major challenge for canola germination and establishment. If tilling clay soils, they should be tilled at a slightly drier moisture content (concentration) than field capacity. At this stage, the moist clay can be squeezed by hand into a pliable ball but no free water appears on the soil or hand.

Medium textured (loam) soils are more forgiving than clay or sandy soils and are best worked when moist. Loam soils worked wet can still create clods, while excessive tillage can reduce them to a very fine structure that can crust or be vulnerable to erosion.

Ensure that any spring tillage prior to seeding is kept to a shallow depth of two and half to five centimetres (one to two inches) since soils tend to quickly dry out to the depth of tillage. Canola differs from cereals in that canola’s small seed size slows and reduces emergence from deep seed placement, so placing seed deeper than what is recommended to reach moisture can significantly reduce seed emergence and survival. If the top five to seven and a half centimetres (two to three inches) of the soil has dried out, increasing seeding depth to access this moisture cannot be done without increasing the risk of reduced plant populations. However, seeding shallow will mean relying on subsequent rains for germination and emergence.

Excessive tillage can create loose, dry seedbeds that are susceptible to erosion. If this occurs, firming the seedbed with harrow/packing operations can be considered, keeping in mind that excessive passes or pressure may further dry out the seedbed and pulverize the surface structure, which increases the risk to soil crusting and erosion.

A firm, well-packed seedbed will:

  • provide good seed-to-soil contact for moisture absorption during germination
  • retain soil moisture in the seed zone
  • provide adequate aeration
  • facilitate uniform shallow seeding depth

A rule of thumb to assess seedbed firmness is to ensure the seedbed is firm enough that footprints are no deeper than the thickness of the sole of a boot.

Packing pressure

In conventional tillage systems, packing can be used before or after seeding (instead of during, as most seeding implements are now equipped with them) to firm the seedbed. Packing operations reduce soil granule and pore sizes at the surface, which reduces soil moisture losses. However, packing the soil too much can cause the soil granules can be pulverized (restricting water infiltration), aeration, and predisposing the soil to crusting and erosion.

On-row packing pressure during seeding is beneficial, especially for canola. It can be challenging to determine the packing pressure to apply during seeding. Not enough packing pressure can result in poor emergence if dry conditions prevail after seeding, while too much pressure can increase the risk to erosion or crusting if wind or heavy rain occurs shortly after seeding.

Generally, pre-seeding soil packing was found to be more desirable than post-seeding packing in conventional tillage system experiments because it will enable more uniform, shallow seeding (carried out by the Canola Council of Canada in the 1990s). Post-seeding packing by rolling is occasionally used to firm up the seedbed and push down rocks. This is not recommended as it increases the risk to soil crusting and erosion, and may actually bury the seed to a depth greater than desired.

Fall tillage to place fertilizer, control weeds, or incorporate crop residue can be beneficial if it avoids extra spring tillage that can dry out the seedbed. Fall fertilization also can take advantage of lower fertilizer prices and reduce labour requirements during seeding. Furthermore, the incorporation of a fall-applied granular herbicide is an effective integrated pest management option, especially if the applied product is a herbicide group used less frequently than others on the same field.

Summerfallow and chemfallow

The amount of area left as summerfallow in Western Canada have been declining over the past couple decades, and now account for less than a million hectares each year 2. If canola is planted on summerfallow, enough crop residue must be left on the soil surface to reduce the risk to soil erosion and crusting.

Reasons to consider practicing summerfallow include:

  • weed control
  • soil moisture conservation
  • increased short-term nutrient availability
  • reduced residue-borne plant diseases
  • reduced risk of crop failure due to drought

Conservation summerfallow maintains sufficient amounts of plant residue on the soil surface to reduce soil erosion, while controlling weeds and increasing soil moisture reserves. Tillage operations are reduced in number or intensity, and are replaced with herbicides (chemfallow). By using residue-conserving practices, adequate cover can be maintained through the fallow period until the next crop is sufficiently established to reduce the risk of soil losses to erosion. Use a minimum residue cover of 1,513 kilogram per hectare  (1,350 pounds per acre) to protect most soil types from harmful wind or water erosion events. This is roughly equivalent to the amount of residue left after harvesting a wheat crop yielding 785 kilogram per hectare (14 bushels per acre) of grain. In practice, most cereal fields will have crop residues that exceed this level. Residue levels are reduced through natural decomposition (sunlight, oxidation, and microbial activity). Canola residue breaks down and decomposes about twice as fast as wheat, making summerfallow after canola a risky practice. Residue cover declines after each tillage operation (Table 1).

Table 1. Residue Left on the Soil Surface after Various Tillage Operations

Tillage operations can be managed to maintain surface residues while preventing serious erosion. Residue left standing in the field will help trap snow and increase spring soil moisture. Usually 45 per cent of soil moisture conserved in an 18-month fallow period is received over the first fall and winter. By trapping snow more effectively, more soil moisture can be conserved. This increased moisture conservation can reduce the need for summerfallow and allow more continuous cropping.

Conservation tillage

A survey conducted in 2012 reported that 87 per cent of the 996 canola growers surveyed in Western Canada practiced conservation tillage 1. Of the three conservation tillage subgroups:

  • 40 per cent of respondents practice no-till or zero-till
  • 30 per cent practice minimum or reduced till
  • 17 per cent practice direct seeding

Major advantages of conservation tillage systems may include:

  • reduced soil erosion by wind and water due to the retention of – and protection from- surface residue
  • maintained or increased soil organic matter content (concentration) in the soil
  • increased soil microbial and faunal populations
  • increased soil moisture storage and infiltration rate
  • improved soil tilth
  • reduced nitrogen and sulphur leaching losses
  • reduced root diseases
  • reduced salinization
  • reduced overall machinery investment
  • reduced labour needs
  • reduced energy requirements
  • comparable or better yields and net returns

Potential disadvantages of conservation tillage:

  • lower spring soil temperatures that can reduce and delay seedling emergence
  • inadequate and expensive seeding equipment for direct seeding into heavy residue conditions
  • limited use of tillage as a weed control tool (increased reliance on herbicides for weed control)
  • increased foliar disease from residue-borne inoculum
  • increased nitrogen denitrification with higher soil moisture
  • delayed seeding in spring due to high soil moisture, with potential for greater unseeded acres in wet years
  • increased surface soil compaction

Direct seeding

direct seeding leaves soil undisturbed from seeding through to harvest, but may disturb the soil more than a no-till system. This increase in soil disturbance at seeding may help to solve immediate weed problems and appropriately address high moisture and heavy clay soil conditions.

The amount of soil disturbance during direct seeding varies with the type of opener. Low soil disturbance direct seeders work less than 40 per cent of the soil surface by the openers to form the seedbed furrow. Some soil from the opener’s action may be deposited between furrows, giving the appearance of more soil disturbance. Low soil disturbance can be expected from 7.5 centimetres (three inches) wide openers spaced at 22.5 centimetres to 30.0 centimetres (nine to 12 inches). Soil firmness, soil moisture conditions and seeding speed affect the amount of soil disturbance.

High soil disturbance direct seeders disturb more than 40 per cent of the soil surface. Wide ground openers that overlap will disturb the entire soil surface to some degree. Sweep openers give varying degrees of weed control, so a pre-seeding herbicide application may not be needed. However, this style of opener may stimulate weed growth since weed seeds and volunteer seeds from the previous crop will be incorporated into moist soil. Furthermore, high disturbance openers may require additional seedbed finishing to cover the seed and to improve weed control.

Seeders and drills

Air seeders and drills have many options and adaptations designed for different soil and field conditions. An air seeder’s mainframe is supported and controlled by wheels inside the frame. Leveling (fore-aft) is controlled by caster wheels in front of the frame (floating hitch type). This method of depth control is superior on land with sharp hills or gullies, and separate soil finishing passes may be needed to ensure good seed placement depth.

An air drill is an adaptation of the air seeder. The main difference between the two is that air drills do not have wheels inside the frame supporting the ground opener hardware. Machine support and depth control comes from dedicated packer wheels on the rear of the drill. The front is carried and controlled by forward caster wheels as with any floating hitch cultivator.

An air drill has two main advantages over an air seeder:

  • relatively constant packing force delivered by each on-row packer wheel.
  • increased residue clearance made possible by the absence of inside-the-frame wheels.

When choosing a direct seeding seed opener for canola, look for an opener that:

  • provides adequate separation between the fertilizer and seed bands.
  • does not allow seeds to fall in a concentrated fertilizer band.
  • creates a good soil structure (fine aggregates) in the seed row.
  • has low draft requirements and resists wear.
  • scours well in moist and high clay content soils (many openers tend to build up with soil, resulting in a larger furrow opening and seed not being covered with sufficient soil).
  • leaves the soil surface smooth for subsequent field operations, like spraying and harvesting.
  • adequately darkens the soil surface over the seed row, resulting in soil (and not residue), over the seed row, especially when soil temperature for rapid seed germination and emergence is a priority.

Opener considerations

Opener performance is influenced by:

  • soil moisture content (concentration)
  • soil texture
  • soil density
  • seeding depth
  • tractor/implement speed

Choosing ground openers to best suit the conditions of a farm is challenging, but achievable. Seed must be placed into moist soil, and surrounded by soil particles small enough to reduce open spaces in the seedbed. Coarse soil lumps in the seedbed increase soil moisture loss and reduce seed germination. For optimal seed-to-soil contact, ensure the ground opener either causes very little soil movement so that the soil profile fracturing is minimized, or causes enough agitation to create soil particles small enough to fall around the seed. The latter may require harrowing to spread the soil over the seed row. Soil cover depth is measured after the last implement passes over the seeded field.

Additional passes with equipment using on-row packing wheels, harrows, or other soil leveling and packing equipment will change the soil cover depth above the seed.

Single and double shoot seeding systems

A single shoot seeding system has only one delivery line going to the ground opener, which transports seed, and sometimes granular fertilizer, to the seed row at a pre-determined depth. A double shoot system has two lines going to the opener, which can be two airflow lines or an airflow line and a liquid fertilizer or anhydrous ammonia (NH3) line. In a double-shoot system the soil buffer is the zone between the fertilizer band and seed row where there is neither seed nor fertilizer. The opener, since it is placing both the seed and the fertilizer, must leave a soil buffer of at least 1.3 to two centimetres (0.5 to 0.75 inches). To achieve this buffer width, the spacing between the centers of the fertilizer and seed outlets must be at least five centimetres (two inches). Seed that lands in the fertilizer band may not germinate or may result in delayed emergence.

Some openers spread seed and fertilizer over the same horizontal plane, providing separation by using more of the seedbed width.

Independent link openers (or floating openers)

With this system, each opener follows the contour of the field independent of the drill’s main frame. Each opener has its own depth control adjustment, which ensures accurate seed depth at every opener.

These openers often form two distinct furrows — one for fertilizer and one for seed. The seed opener follows behind and slightly to the side of the fertilizer point, ensuring that soil covers the fertilizer band before the seed is placed. There is little chance of fertilizer and seed mixing.

Selecting and using ground openers

All commercially available openers work under some conditions, but few, if any, work well under all conditions. To find out if a particular opener design will work well under the conditions on a particular farm:

  • Discuss ground opener performance with neighbours to learn more about options suited to the conditions local to your farm.
  • Determine which openers will meet the requirements for seed and fertilizer placement, handle the amount of residue cover that usually exists on the farm, and meet other requirements specific to the operation — such as providing some weed control.
  • Install one or more of these openers on the seeder, try them in several typical conditions on the farm and assess the results.
  • If available, review and consult local research trials that have tested different styles of openers under different field conditions.

Ground opener design is often influenced by soil and crop residue conditions in the area where the opener was developed. If these conditions are similar to the grower’s farm, chances are greater that the opener will do a good job. Therefore, ask the manufacturer about the conditions in the area where the opener was developed.

Some tips for opener use in direct seeding:

  • Check settings in each new field and in areas of the field where conditions are different. Compromising this step can be costly in terms of stand establishment, and subsequently, in yield.
  • No particular opener will work well on all soil textures. If a farm has multiple of soil textures, openers may have to be changed to suit certain fields and their respective current conditions.
  • Double shoot openers may require frequent adjustment of depth and forward speed to ensure proper placement with adequate separation of seed and fertilizer.
  • When soil conditions are very moist, particularly in fine clay soils, ensure the seed row furrow is sealing or closing adequately to preserve seedbed moisture. Also ensure packer wheels are not building up with mud or pulling up seed with mud clods.
  • When assembling components from several sources, pay special attention to ensuring good assembly and mechanical compatibility.
  • Take the time to level all components.

Canola and conservation tillage

Weed control

Research on the Prairies has found that clear changes in weed communities do not generally occur with the adoption of conservation tillage seeding. Weed communities are more influenced by location, crop rotation, and environmental conditions for a particular year. An Agriculture and Agri-Food Canada study at Rycroft, Alberta compared the impact of three tillage systems (conventional, reduced and zero-till systems) on the weed population during early crop growth. The study found that the relative contributions to the size and diversity of weed flora are likely to be greater by common species under conventional tillage and by rare species under reduced and zero-tillage systems. No consistent increase in the weed population occurred with time among the three systems tested.

Similarly, an Agriculture and Agri-Food Canada study at three Saskatchewan locations from 1986-1990 did not report an increase in perennial and annual grass weeds in zero tillage systems. This study also found that weed community changes were influenced greater by location and year than by the tillage system.

Certain weeds (such as dandelion, narrow-leaved hawk’s beard and foxtail barley) can proliferate under direct seeding if not carefully managed. Given the environment found in direct-seeded fields, weed species with adaptation to residue-covered habitats will become dominant over species commonly found in conventional, cultivated fields. But research indicates that weed shifts are manageable by careful attention to crop rotations and sequences, herbicide group selection, and timing (especially pre-harvest glyphosate for perennials). Herbicide-tolerant canola systems have allowed for effective options for weed control in direct seeded systems.

Soil moisture and moisture use

Increased soil moisture reserves under conservation tillage practices is due to reduced evaporation from residue-covered soil, as well as increased infiltration rates. In addition to increased spring soil moisture, an Agriculture and Agri-Food Canada study from Scott, Saskatchewan reported greater yield in zero-till systems as well as greater moisture use efficiency in the majority of the zero-till sites tested 3.

However, in excessively wet years, canola growth, water use efficiency and yield can suffer under direct seeding.

Soil temperature

Spring soil temperatures are often cooler under conservation tillage seeding systems than conventional tillage. Most of the western Canadian research studies have found that residue covered soil is up to two degrees Celsius cooler (daily average temperature) than cultivated soil. In some cases, for example, during days with little cloud cover, temperatures during midday can vary by five degrees Celsius. The lower soil temperature is due to increased soil moisture (water is slower to warm up than air) and more heat reflectance by the residue. Although emergence is sometimes several days slower under direct seeding practices compared to conventional ones, this delay usually disappears after canopy closure. Increased soil moisture usually improves yield despite the initial cooler temperatures in the spring.

In most cases, cooler soil does not reduce final plant stand or yield. Direct seeders can often seed shallower (where it is warmer) due to more moisture at this depth, which compensates for temperature differences.

Frost damage to canola seedlings has been more severe on residue-covered fields when frost was followed a warm sunny day. The greater injury is likely due to lower heat radiation in the critical early morning period under residue-covered soil compared to bare soil. Close attention to achieving uniform residue spreading, preferably with the combine, to reduce low temperature problems and enable good ground opener performance and seed placement is recommended. Research by Agriculture and Agri-Food Canada in the Peace River region found that a narrow strip of bare soil over the seedbed can overcome most of the cool temperature and excessive moisture disadvantages of direct seeding in unfavourable situations.

Research conducted on the Prairies has reported inconsistent results with conservation tillage seeded canola. zero-till or direct-seeded canola has yielded less, the same or more than conventionally seeded canola. The many changes in direct-seeding technology and variable environmental conditions make it challenging to apply past research findings to the farm level.

Yield records from Agriculture Financial Services Corporation in Alberta shows that direct seeding and reduced tillage account for most of the canola acres in Alberta, and produced higher yields, on average, than conventional tillage through 2009-2011.

Footnotes

  1. Agriculture and Agri-Food Canada (for the Canola Council of Canada). 2012. Survey of management practices used by canola producers in Western Canada: Final Report. Based on survey by BlackSheep Strategy.
  2. Statistics Canada.2016. Agriculture Census data: Table 32-10-0412-01. Forms of weed control on summerfallow land. doi.org/10.25318/3210041201-eng
  3. Brandt, S.A. 1992. Zero vs. conventional tillage and their effects on crop yield and moisture. Can. J. Plant Sci. 72: 679-688.

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