Soil Management Guide
Tillage, Organic Matter and Crop Residue Management
A. Tillage
Defining Tillage Systems
There are two main types of tillage systems: conventional tillage and conservation tillage. Conventional tillage is a system that traditionally uses moldboard plows or chisel plows with sweeps, followed by disking, harrowing or other secondary tillage operations to incorporate residue, prepare a seedbed and control weeds. Conservation tillage systems, which include reduced tillage and zero tillage, produce benefits such as soil quality enhancement (increased soil organic matter levels over time), moisture conservation, erosion control, reduced use of fossil fuels and reduced labour requirement. Weed control in these systems may require increased use of herbicides. There are a variety of conservation tillage systems, as described below. Reduced tillage systems involve the removal of one or more tillage operations to increase residue cover on the soil, reduce fuel costs and to use standing stubble to trap snow to increase soil moisture and permit the winter survival of winter wheat. Three examples of reduced tillage systems:
- Direct seeding is a type of reduced tillage where the only tillage operation occurs at seeding. Maximum surface residue is maintained until seeding, at which time high disturbance seed openers are used for seedbed preparation, residue management and weed control.
- Ridge till is a type of reduced tillage where row crops (such as corn) are planted on pre-formed ridges. During the planting operation, crop residues are cleared from the row area and moved to the furrow between rows. The planted rows are on a raised ridge 3 to 5 inches (7.6 to 12.7 centimetres) above furrows between rows. Ridge height is maintained with cultivation. Weeds are controlled with cultivation and/or herbicides.
- Minimum tillage is a type of reduced tillage that employs a reduction in one or more tillage operations from conventional practices (such as no fall tillage) and uses low disturbance seed openers.
Zero tillage (or no-till) is a type of cropping system in which crops are planted into previously undisturbed soil by opening a narrow slot of sufficient width and depth to obtain proper seedbed coverage. No tillage operation for the purpose of weed control is conducted, but this allows for tillage with low disturbance openers (knives, spikes, etc) for fall banding of fertilizer, filling in ruts, and the use of heavy harrows for crop residue management.
Zero tillage is often thought of as the “ultimate” in conservation tillage. The use of narrow, low disturbance openers (knives, discs) on the seeder results in minimal seedbed disturbance. All of the other tillage systems produce higher soil disturbance, either from wider, high disturbance openers (sweeps, spoons) or from the inclusion of a tillage operation for the purpose of weed control.
Regardless of the type of conservation tillage system, all will result in lower seedbed disturbance/fewer passes than in a conventional tillage system.
Table 8.1 Comparisons of various tillage systems*
| Tillage System | Fall Tillage | Spring Tillage | Soil Disturbance | |||
| Seed openers | Overall System | |||||
| Conventional tillage | Yes | Yes | Low or High | High | ||
| Conservation tillage | Reduced tillage | Direct seeding | No | No | High | Moderate |
| Ridge tillage | Yes | No | Ridge planters | Moderate | ||
| Minimum tillage | Spring OR Fall | Low | Moderate | |||
| Zero tillage | No | No | Low | Low | ||
*Adapted from Definition and Verification of Tillage Systems Used for Pilot Emissions Reductions, Removals and Learnings Initiative (PERRL), 2004 Draft Low disturbance openers are narrow openers such as knives, narrow spoons, narrow hoes and slightly offset discs (not including a discer). The openers should not disturb more than 33% of the soil surface area (eg. If the opener row spacing is 9 inches (22.9 centimetres), then the width of disturbance created by a single opener should not exceed 3 inches (7.6 centimetres). High disturbance openers are medium and wide openers, such as wide hoes, narrow sweeps or shovels, wide spoons, wide shovels and discers. These openers disturb more than 33% of the soil surface. For more information refer to the Zero Tillage Production Manual and Advancing the Art by the Manitoba-North Dakota Zero Tillage Farmers Association.
B. Organic Matter Depletion
Organic matter is an important component of soil that supplies plants with nutrients, holds soil particles together to prevent erosion, and improves soil tilth, which refers to the degree to which the soil is aggregated together and suitable for agriculture. Organic matter also improves water infiltration and water-holding capacity while controlling the decomposition and movement of some pesticides. Biological processes of plant growth and human activities, such as tillage, have affected the present state of soil organic matter.
 Figure 8.1 Trends in soil organic matter content (Brady,1999) |
Typically, soils in agro-Manitoba range from 2 to 7% organic matter. These lands in a native state, prior to settlement and cultivation, had organic matter levels in the range of 10 to 15%. For the first 25 to 50 years, little to no commercial fertilizer was added to the soil because the nutrients released in the decomposing organic matter were ample to grow a crop. The decomposing organic matter resulted in depleting soil organic matter levels. The rate of depletion has now leveled off and organic matter levels are relatively stable, but fertilizers are invariably required most years on agricultural soils to provide sufficient nutrients to grow a crop. The trend in organic matter depletion is variable and site specific. Practices such as conservation tillage, forages in the crop rotation, and the addition of crop residues and livestock manure can maintain or increase soil organic matter content over time. However, row crop and special crop production, such as potatoes and edible beans, results in more tillage, less plant residue produced by crops and less residue returned. This may deplete soil organic matter levels. Soils with increased organic matter have desirable structure that tends to crumble and break apart easily and is more suitable for crop growth than hard, cloddy structure.
Consult soils report
It is important to ask the following questions when considering adoption of any conservation tillage practices:
- What are the texture and drainage of the soils at the site in question?
- What are main agriculture capability limitations?
- What soil conservation practice(s) would most likely benefit the soil type in question?
Agriculture capability ratings from the soils report have implications for which, if any, conservation tillage practice should be adopted.
Table 8.2 Agriculture capability limitations and implications for conservation tillage practices
| Ag Cap | Effect of tillage |
| E | Tillage increases susceptibility of soil to all types of erosion |
| M | These are typically sandy soils that would benefit from conservation tillage |
| N | Salt affected soils are worsened by tillage as salts are brought to the surface |
| T | Tillage on slopes results in tillage erosion and increases the risk of water erosion |
Site Assessment
- Determine the equipment used for: primary tillage, secondary tillage, seeding, spraying, harvesting, chaff and straw management
- Determine crop residue cover
- Earthworm populations are an indicator of soil quality. Earthworms generally increase soil microbial activity, increase soil chemical fertility and enhance soil physical properties. About 10 earthworms per square foot (100 per square metre) of soil is generally considered a good population in agricultural systems (Soil Quality Test Kit Guide, 1998).
Recommendations
- Adopt some form of conservation tillage.
- Consider chaff and straw management equipment options (contact Prairie Agricultural Machinery Institute for individual equipment assessment). Keep in mind that standing stubble is 1.6 times more effective at controlling wind erosion than flat stubble.
- Tillage can easily dry out the soil profile (eg. 1 tillage pass removes 0.5 inches (12.7 millimetres) of water) and increase the risk of wind erosion. Tillage when soils are too wet can result in soil compaction.
- Moving 4 to 6 inches (10 to 15 centimetres) of topsoil upslope from the lower areas of the field and placing it back onto the eroded knolls (landscape restoration) has restored yield potential to affected portions of fields that could not be achieved by simply adopting zero tillage techniques (Dr. David Lobb, Department of Soil Science, University of Manitoba, personal communication).
Follow-up monitoring
- Keep records of crop yields
- Soil test for organic matter, nutrient status, etc.
- Measure earthworm populations. Earthworm populations are patchy within a field and vary with time of year. Count earthworms in spring and fall and use the averages to gauge changes from year to year (Soil Quality Test Kit Guide, 1998).
- Measure a square foot and dig down 12 inches (30.5 centimetres) with a shovel or trowel, minimizing the number of cuts to avoid damage to the earthworms. Dig the hole first, then sort for earthworms. Make sure the bottom of the hole is level.
- Sort the samples against a pale-coloured background to help locate the earthworms. Separate and count the number of earthworms.
- To extract deep burrowing earthworms, add 2 L of mustard solution (2 tbsp. mustard powder + 2 L tap water) to the hole. Deep burrowing earthworms should appear within 5 minutes. Count the number of worms.
- Record total number of earthworms found at the inspection site. Rinse earthworms in clean tap water and return to hole.
- Repeat.
C. Crop Residue Management
Depending on the climatic conditions and soil type, the amount of crop residue produced may vary from place to place and over time. In times of drought and on soils prone to erosion, maximizing the amount of crop residue produced is beneficial. In wet years and on heavy clays, large amounts of crop residue can be difficult to incorporate and results in cold, wet soils in the spring. As a result, many producers resort to burning the crop residue, but this destroys soil organic matter, removes nutrients and causes problems from the smoke generated. On these soils, producing less crop residues is preferred. The following management practices should be considered.
Spring:
- Cereal variety selection – straw height and lodging rating should be considered. Refer to Seed Manitoba crop variety data for more information.
- Soil test for N (0 to 24 inches (0 to 60 centimetres)) – excessive amounts of nitrogen produces higher vegetative growth and increases the susceptibility to lodging. Follow recommendations based on reasonable and attainable target yields – refer to the Soil Fertility Guide for more information.
- Earlier seeding usually results in shorter straw.
Table 8.3 Estimating straw yield from grain yield of selected crops
| Grain | Pounds of straw per bushel of grain |
| Wheat | 100 |
| Barley | 48 |
| Flax | 70 |
| Canola | 110 |
| Peas | 100 |
(e.g. A 40 bu/ac (2700 kg/ha) wheat crop produces approximately 4000 lb/ac (4500 kg/ha) of straw)
Summer:
Harvest Options
- The amount of crop entering the combine depends on harvest method, each of which has its benefits and drawbacks:
- swathed wheat crop: 85% straw, 15% chaff entering combine
- straight-cut wheat crop: 70% straw, 30% chaff entering combine
- stripper header: even less residue entering combine than the above methods, resulting in faster harvesting time, but a separate pass may be required to manage the straw, along with challenges of straw flattened by equipment traffic
- Ensure optimum combine straw chopper performance
- Keep knives sharp - if possible, avoid harvesting a crop when straw is wet because it requires more power to chop and does a poorer job of chopping straw into short pieces
- Set fins for maximum spread – spreading straw 70% of the width of cut is recommended (eg. In a 30 foot (9 metre) swath, spread straw 21 to 24 feet (6 to 7 metres))
- Consider upgrading to a “fine cut” chopper – finely chopped straw requires 30 to 40 hp from the combine
- Consider opportunities for baled straw:
- livestock bedding and feed
- composting ingredient
- alternate uses (heating fuel, erosion control, building material, etc.)
- Manitoba Agriculture, Food and Rural Initiatives has a free hay listing service where producers submit hay and straw they have available for posting on the internet. Those looking for hay or straw can search the database and contact the producer directly. Manitoba Hay Listing Service
- Crop reside burning should be avoided using other management practices, such as those listed above. However, if you must burn, crop residue burning daily authorizations begin August 1 – consult Manitoba Agriculture, Food and Rural Initiatives’ website: Manitoba Crop Residue Burning Program Daily authorizations are also sent to radio stations, RCMP detachments and to the offices of Manitoba Agriculture, Food and Rural Initiatives, Manitoba Conservation and Manitoba Health throughout agro-Manitoba by 11:00 am.
Fall:
- Fall-applied liquid hog manure, at agronomic application rates, may increase the decomposition rate of crop residues (MacLeod et al, 2002)
- Stubble height after harvest should be similar to the shank spacing of the equipment used for the next field operation (fall or following spring)
- Heavy harrows should be set for maximum tine angle (as vertical as possible) without causing bunching
- Tillage options are presented in Table 8.4
Table 8.4 Amount of straw buried per pass of selected tillage implements
| Implement | Amount of straw buried per pass (%) |
| Heavy harrows (steel tooth, >12") | 5 |
| Wide blade cultivator (sweeps >3 ft) | 10 |
| Heavy duty cultivator (sweeps 8-12") | 20 |
| One-way disc | 40-50 |
| Heavy tandem or offset discs | 40-60 |
| Moldboard plow | 90-100 |
Table 8.5 Cost of fuel and equipment per fall tillage pass (Farm Machinery Rental and Custom Rate Guide, 2001)
| Equipment | Cost |
| 300 hp 4WD tractor | $2.05-2.45/ac |
| Fuel | $0.95-1.23/ac |
| Heavy duty cultivator | $1.05-1.30/ac |
| Total | $4.05-4.98/ac |
Note: Residue management may differ for winter wheat survival. For winter wheat crop to survive the winter, an adequate layer of snow cover is required to keep the crop insulated.
Snow Trapping Potential (STP)
“The most successful way to maintain adequate snow cover is to retain the greatest possible height and density of standing stubble. Harvest the preceding spring crop as high as possible and thoroughly spread the harvested straw and chaff. Special attention must be paid to maintaining standing stubble in high traffic areas such as field approaches and headlands. Use the snow trapping potential index to measure your snow trapping potential:
STP = [stubble height (cm) × stubble stems per m2]/100
A snow trapping potential index greater than 20 is acceptable; less than 20 indicates a high risk of winter injury, particularly for winter wheat and triticale. Based on the stubble disturbance of your seeding equipment, you may need to set pre-seed STP targets of 40 or more. For reference, cereal stubble typically has pre-seed STP’s of 80 or higher, while canola and flax are normally in the range of 30-50, depending on stubble height.” (Winter Cereals Canada, Winter Cereal Production Reference Guide).
If You Must Burn
- Account for nutrient losses from burning straw. Straw that is removed by baling transfers the nutrients in straw for use in another area – straw removed by burning removes nutrients from the field with no subsequent economic benefit and destroys organic matter from intense heating. This emphasizes the need to maximize the use of straw in the field or at least recognize the economic value of straw in terms of its nutrient content.
- Drop straw in tight, narrow swaths for burning.
- Use fire-guards - consider tillage in between swaths or burning in moist conditions to avoid burning the entire field.
- Follow daily crop residue burning authorizations, which are based on suitability of weather conditions for smoke dispersion.
- Fires must be supervised at all times.
- Consider wind speed and direction before burning.
- Consider the health and safety of neighbours and nearby traffic before burning.
Table 8.6 Nutrient content in pounds per tonne of straw and resulting ash (Heard et al, 2001)
| Crop | Nutrient | lb/t of straw | ||
| Straw | Ash | % lost | ||
| Wheat (assumed Yield = 1 t/ac) | C | 911 | 85 | 91% |
| N | 24 | 0.4 | 98% | |
| P | 3 | 2.6 | 18% | |
| K | 32 | 26 | 24% | |
| S | 2.4 | 0.8 | 70% | |
| Ca | 4.4 | 3 | 30% | |
| Mg | 2.3 | 1.7 | 27% | |
| Oats (assumed Yield = 1 t/ac) | C | 918 | 34 | 96% |
| N | 11 | 0.14 | 98% | |
| P | 1.7 | 1.4 | 17% | |
| K | 52 | 33 | 37% | |
| S | 4.9 | 2.4 | 72% | |
| Ca | 4.6 | 3 | 33% | |
| Mg | 3.8 | 2.7 | 31% | |
| Flax (assumed Yield = 0.5 t/ac) | C | 1003 | 31 | 97% |
| N | 31 | 0.06 | 99% | |
| P | 1.5 | 1 | 36% | |
| K | 5.2 | 2.9 | 44% | |
| S | 1.2 | 0.15 | 82% | |
| Ca | 10.3 | 6.7 | 34% | |
| Mg | 3 | 1.9 | 36% | |
From the above table, the C:N ratios for crop residues are 38:1 for wheat, 83:1 for oats and 32:1 for flax. All three crop residues have high C:N ratios which favour immobilization of soil N as the straw is decomposed by soil microbes.
Winter:
Crop Residue Burning authorizations cease on November 15. From November 16 to July 31, burning of crop residues may proceed between sunrise and sunset, subject to health and safety considerations. Night time burning of crop residues is banned year-round.
Spring (Year 2):
The following issues must be considered when seeding into high residue conditions:
- Plugging – match stubble height to the shank spacing of the equipment used for the next field operation (fall or following spring) to reduce the risk of equipment plugging with straw. Coulters and disc openers are less likely to plug than hoe openers, and knives are less likely to plug than sweeps, but less plugging also means less soil disturbance and cooler spring soil temperatures.
- Soil temperature – cooler soil temperatures may result in delayed emergence and increased risk of frost injury; however, this may not impact crop yield.
- Moisture – higher soil moisture may result in improved seeding conditions in a dry spring, but delayed seeding, plugging problems and increased compaction may occur in a wet spring.
- Disease potential – there is no evidence that burning straw reduces the incidence of crop diseases. Crop rotations and environmental conditions are the major factors determining disease pressures.