Soil Management: Reducing Losses of Organic Matter
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811: Agronomy Guide > Soil
Management > Reducing Losses of Organic Matter
Reducing Soil Erosion
Soil erosion occurs to some extent on most agricultural soils. Factors affecting erosion include soil texture, intensity of rainfall, slope steepness, length of slope and management factors such as crop rotation and tillage practices. A number of the measures already mentioned in this chapter can help control or reduce the amount of soil lost from a field. Minimizing the amount of tillage used can reduce tillage erosion. Minimum till, no-till, improved drainage and crop rotation, including cover crops, can go a long way to reducing wind and water erosion. Table 8-13, Soil Management Practices to Reduce Soil Erosion, shows benefits of various practices to water, wind and tillage erosion.
In some situations, these measures are not enough, especially where water flow is concentrated, and other soil conservation practices become necessary. A number of structures can be used to control a concentrated flow that is causing a gully or rill in a field. These structures will require less maintenance if combined with minimum till or no-till. Improved tillage and cropping practices can also reduce the size of the structure required. Strip cropping is another option for protecting the soil from water erosion. This practice involves planting alternating strips of row crops with a cereal or forage. Combining conservation tillage with strip cropping will increase the width of the strips required.
See the booklets Best Management Practices: Soil Management, Order No. BMP06E, Best Management Practices: Field Crop Production, Order No. BMP02E, and the OMAFRA website at www.ontario.ca/crops, for more information.
Stream and Ditch Protection
Ditch and stream banks are often a significant source of sediment in water. Unprotected banks will continue to erode, cutting into valuable farmland. Increasing pressure to protect groundwater and surface water underlines the need to protect this resource. A number of measures can protect stream and ditch banks as well the water flowing in them. High stream flows, cattle and machinery can subject banks to erosion. Concentrated flows entering a watercourse can cause rill or gully erosion. Buffer strips, tile outlet protection or header tile, drop pipes and rock chutes can help stabilize streambanks and ditches.
Restrict livestock from all watercourses; many fencing options are available. Bridges, culverts or low-level crossings are some of the options available to move livestock and machinery safely.
See the Best Management Practices booklets listed at the end of this chapter.
Windbreaks and Shelterbelts
Often additional protection from the wind is necessary when there is not enough residue to hold soil in place. Windbreaks and shelterbelts can provide that protection by slowing down wind speeds near the ground. Windbreaks also create a micro-climate, raising soil and air temperatures adjacent to the trees, reducing drying winds and accumulating more snow. These effects also provide crop yield increases. See Figure 8-2, Windbreaks Provide Protection to Crops.
Fragile Land Retirement
Occasionally, the erosion cannot be controlled on a field or part of a field. The erosion may be too extreme, or the field has some other limitation, making it unprofitable or unsustainable to farm. Fragile land could include areas along creeks, lakes and wetlands that may be subject to flooding or other land that is subject to severe erosion. This land should be retired from production to forest or pastureland.
As discussed earlier, compaction occurs easily with the use of heavy farm equipment, especially when soils are wet.
A number of management options can help prevent soil compaction:
Subsoiling is often used to try to loosen compacted areas of fields where heavy loads have passed. Generally, subsoiling does not provide any long-term benefits. Always check for the presence of compaction using a tile probe or soil pit and check the moisture at depth before subsoiling. See Soil Health Check, for a description of how to detect soil compaction. Deep tillage where the soil is not compacted will not provide any benefit and may damage soil structure or drainage tile below the normal depth of tillage.
Change soil management, harvesting and manure application practices to avoid further problems. These changes include using lighter loads and staying off the soil when it is wet below the surface.
Soil is tilled for a number of reasons. Those include weed control, soil levelling, burying of crop residues, incorporation of fertilizer and manure and seedbed preparation. The advent of herbicides greatly reduced the need for tillage to control weeds (except in the organic system) and the development of equipment to plant into crop residues means that crops can be planted successfully with little or no tillage. Generally, performing primary tillage operations in the spring will leave the soil less prone to erosion than tillage in the fall. Try to use the least amount of tillage necessary to achieve the goal.
See the tillage sections of each specific crop in this publication for additional information.
From a soil quality perspective, the moldboard plow is the least desirable tillage method because it leaves little residue on the soil surface, requires multiple passes of secondary tillage and is energy and labour intensive. Plowing and secondary tillage pulverize aggregates, making the soil more prone to crusting and erosion. If moldboard plowing is used, set the plow to stand the furrows on edge and try to leave some residue on the surface. Also minimize the number of secondary tillage passes to reduce the breakdown of soil aggregates
The chisel plow will leave more residue on the surface than the moldboard plow, depending on how it is set up, amount of crop residue and the amount of secondary tillage used. Chisel plowing with twisted shovel teeth will leave the soil ridged, which is good for soil erosion control but can require extra tillage passes in the spring and lead to uneven soil moisture in the seedbed. Many of these problems can be overcome by:
The chisel plow can also be an effective tool for incorporating manure.
The disc, like the chisel plow, will leave more residue on the
soil surface than the moldboard plow. Using this tool when the soil
is too wet can cause soil compaction. Too many passes will break
down soil aggregates and increase the loss of soil organic matter
and risk of crusting. A good planter set up to handle some residue
and a rougher seedbed can help reduce the number of secondary tillage
passes in any tillage system.
No-Till, Zone Till and Strip Till
No-till systems provide the greatest opportunity to leave protective crop residues on the soil surface. They also have the greatest potential for reducing tillage costs, offset somewhat by the need to control weeds in nearly all cases with a preplant "burndown" herbicide application. Numerous options exist both in the original design and in the modifications available for row crop planters or seed drills to be considered "no-till" capable.
In Ontario, the term "no-till" generally describes planting the crop into a field with no previous tillage passes, with just the seed opener or with one coulter in front of the seed opener. Planting into the soil the spring after fields were tilled in the fall and left ready to plant is not no-till.
Zone tillage systems usually have two or three coulters in front of the seed and fertilizer openers and may also include trash wheels.
Strip tillage utilizes a toolbar with coulters in front, followed
by a shank and a couple of disks at the back. It may be used in
the fall, spring or both to prepare a seedbed. The shank typically
operates at a 10-15 cm (4-6 in.) depth.
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