Soil and Water Conservation

Soil conservation can be advanced through two different approaches. The first is more immediate and consists of finding and applying new techniques so soil degradation and erosion can be stopped and the soil will eventually be repaired. The second one is on a long term basis and consists of establishing within society the philosophy of soil conservation as an integral part of sustainable development and part of everyone's responsibility.

Techniques to promote soil and water conservation

Good land planning

Growing the right crop on the right kind of land is an important technique to fight land degradation. The climate and the nature of soil is the main determinant of the crop that can be grown most successfully. A FAO project (Agro-Ecological Zones) has already determined the areas in the developing countries where the major crops such as pearl millet, maize, wheat, soybean, cotton or rice can be grown better. The slope of the land is also very important in determining the type of crop to grow. For example, any type of crop can be grown on flat land while step terraces are needed on land with a 36% slope.

Good farming management

Growing the crop in a way which is best suited for a type of land saves huge amounts of money, energy and manpower, while saving the soil itself. Actually, proper crop management can reduce the rate of soil erosion by a factor of 20.

Terracing

Below: terraced corn.

Terracing refers to the construction of an earthen ridge with a shallow up-slope channel across the slope to intercept surface run-off, and reduce sheet erosion. To be most effective, terraces should be used in conjunction with other soil conservation measures. (put picture of terraces)

Interseeding

Interseeding allows the soil between rows to be covered from rain drop impact and water run-off.

Crop rotation

Crop rotation is one of the most important management practices in sustainable agriculture, and has benefits that extend to many aspects of the farm operation. Rotation refers to the succession of different crops over the years within the same field. Each crop in the rotation contributes to the removal and addition of organic matter to the soil. Over the complete rotation, the difference between the loss and gain of organic matter should balance in order to avoid soil exhaustion (Rotation des cultures et engrais verts, 1993).

Benefits of crop rotation

• Breaks pest cycles by rotation with non-host crops
• Allows soil to rebuild its nutrient reserves after a demanding crop such as corn
• Saves money on fertilizer inputs
• Legume crops provide nitrogen for the following crop, and improve soil structure
• Increases yields
• Reduces soil erosion
• Spreads out cropping workload over the growing season

Strip cropping

Below: strip cropping of soya beans and apple trees.

A field planted with alternating strips of two or more different crops, such as corn with soya, or corn with a cereal such as barley, is referred to as strip cropping. This cropping system offers advantages of crop rotation (within the same field in the same year) combined with protection from wind and water erosion.

Vegetative buffer strips

Vegetative buffer strips established along the edge of a watercourse can stabilize fragile banks suffering from erosion caused by run-off and prevent streams or drainage ditches from being filled with soil sediments.

Watercourse surroundings and ditch banks are fragile areas susceptible to degradation and erosion if not properly protected from agricultural practices and adverse seasonal conditions. Grassed cover protects the soil and holds the banks, which helps to prevent soil accumulation within the watercourse. Wooded strips are known to retain up to 90% of sedimentation from agricultural land (Document de réflexion sur la bande riveraine de protection, 1996). Over the years, bank degradation widens the watercourse to the detriment of agricultural land. Besides the loss of cultivatable land, this watercourse enlargement reduces water velocity and the movement of sediments, leading them to be deposited at the bottom. Blocked drains, damage to wildlife habitat and increased maintenance costs are other consequences of watercourse bank erosion.

Benefits of vegetative strips

• Stabilizes watercourse banks
• Provides a sediment filter or barrier to surface water flow
• Prevents water warming
• Regulates the hydrologic cycle through plant evapo-transpiration
• Filters nutrients from agricultural land and prevents them from reaching groundwater or watercourses
• Can serve as a travel lane or turning lane for adjacent fields (take care to lift tillage equipment, or turn off spraying equipment to protect vegetation)
• Creates habitat for fauna and flora
• Can act as a natural windbreak, depending on the vegetative species utilized.

Cover crops

(also called "green manure") Cover crops are grown to cover the ground with living plant matter or dead mulches to protect soil against water and wind erosion in winter, and against heavy rains and surface run-off in spring. In addition to controlling erosion by blanketing the soil, cover crops also add organic matter, thus increasing soil aggregate strength, and holding the soil in place. Some of the legumes, grasses, and cereals often grown as cover crops are crimson clover, red clover, vetch, oilseed radish, winter rye, perennial rye, and buckwheat.

Benefits of cover crops

• Decreases loss of nutrients and pesticides associated with surface run-off
• Improves soil structure
• Improves water infiltration and soil aeration
• Legume cover crops fix atmospheric nitrogen into the soil that then becomes available for the next crop
• Non-legume cover crops take up soluble nutrients, preventing leaching
• Residues regulate surface temperature, conserve moisture and slow the breakdown of organic matter
• Weed suppression
• Enhances biological diversity, which generally favors pest predators
• Provides food and cover for earthworms and other soil fauna during over-wintering

Crop residue

Management of crop residue is one of the most efficient techniques for controlling soil erosion. The risk of erosion can be reduced by half by leaving 30% of the soil surface covered. Conservation tillage systems are employed to leave adequate residue.

• Protecting the soil surface from the direct impact of raindrops
• Creating a rough surface to slow down the velocity of run-off water
• Protecting the soil surface from wind
• Improving soil structure and aggregate strength by adding organic matter
• Providing a slow release of nutrients to the crop
• Increasing water infiltration.

Contour cropping

When growing crops on sloped land, contour cropping can greatly reduce erosion by tilling and planting across, rather than up and down, the hill. The curvature of the land must be followed. Tilling with the contour or cross-slope, is easier with chisel plows or offset discs than with a moldboard plow.

Limited livestock access to watercourses

Below: a cow grazes.

Livestock have a mostly negative influence on a watercourse and its water quality. They graze and trample stream bank vegetation and push soil directly into the water. Livestock defecate directly into the stream, and in turn drink from the same supply which, depending on available volume and velocity, may not be fit for consumption.

Fencing a watercourse to eliminate livestock access reinforces bank stability, reducing sedimentation and associated pollutants. Maintaining the quality of the water mitigates the need for watercourse cleanup, and encourages wildlife and aquatic life. Offering livestock a clean, alternate watering facility reduces the risk of transmitting disease organisms.

Tillage practices

Tillage erosion can be reduced by changing tillage patterns, and decreasing the depth and speed of tillage operations. Fields plowed in the same direction every year become more susceptible to erosion, with increased losses in some areas, such as sections regularly plowed downslope.

Minimum tillage

Also known as reduced or mulch tillage, minimum tillage systems disturb the soil at some time between harvesting one crop and planting the next, but leaves at least 30% of the soil surface covered with residue after planting. Primary tillage is done with disc or chisel plows, and secondary tillage is kept to a minimum to conserve residue. This type of tillage system is well-suited to resolving soil conservation concerns, especially ones associated with the use of forages and manure (Best Management Practices: Field Crop Production).

Conservation tillage

Conservation tillage is any tillage system which provides a suitable seedbed while leaving enough protective crop residue on the soil surface. Generally, 30% residue cover is the minimum required to sufficiently protect the soil surface throughout the growing season. The number of tillage passes must be minimized, as each pass breaks down soil aggregates and buries crop residue, lessening their effectiveness in erosion control. The different systems considered as conservation tillage are minimum till, ridge till, and no-till. Variable in their management practices, they also leave different crop residue percentages on soil surfaces .

Other benefits of conservation tillage

• Decreased labor and fuel costs
• Decreased compaction and crusting associated with poor soil structure
• Increased microbial life which speeds breakdown of pesticides
• Mulch from residue conserves moisture in the summer by protecting soil surface from sun and wind
• Increased macropore formation

Ridge tillage

In this tillage system, row crops are grown on permanent ridges of soil built with a modified cultivator. Except at planting time, no other tillage operation is performed. Residue is left on the soil surface and may be sliced off the top of the ridge just prior to seeding. Soil compaction is limited to the area between the ridges, eliminating soil structure damage to the root zone. Crop yields obtained in ridge tillage are generally comparable or even higher than with no-till (Ridge-Till Systems).

Interesting facts about ridge tillage

• Suitable for soils with poor drainage because the ridges dry out and warm up sooner
• Weed population between rows is slowed by spring temperature difference and crop residue moved from ridges
• Reduces herbicide use by banding in the row and cultivating between the rows
• Chemical fertilizer inputs can be decreased by band application
• The preferred method of manure application is liquid injection into the rows
• The ridges act like little terraces, greatly reducing erosion and run-off Generally not used for forage crops (Best Management Practices: Field Crop Production)