Other Problems related to Agricultural Practices

Soil compaction

Soil compaction prevents the proper development of plant root systems. Over the years, repeated travelling of over-loaded machinery through fields or in wet conditions leads to soil particles being packed closer together, increasing the density of the soil and limiting natural processes such as aeration and water infiltration. This impact on soil structure can be minimized through adequate management.

Problems associated with soil compaction

• Decreased yields
• Increased run-off
• Increased soil erosion
• Poor drainage
• Loss of phosphorus

Signs of compacted soil

• Hard, dense layers without macropores in the soil
• Water puddling
• Development of plow pan
• Increased power requirements during tillage
• Uneven crop stands
• Plants are water stressed
• Nutrient deficiencies in crops
• Crop roots growing down, then sideways
• Root tips are flattened and/or swollen
• Earthworm populations are lower than usual

Reducing the risks of compaction

• Avoid working the soil when it is too wet
• Minimize the number of trips over the field
• Limit machinery traffic to controlled areas of the field
• Reduce vehicle weights
• Improve drainage
• Use large diameter tires
• Use tractors with 4-wheel drive for better weight distribution than 2-wheel drive
• Include deep-rooted forages such as alfalfa or sweet clover in the crop rotation to break up the soil

Soil crusting

Excessive seedbed preparation or packing of the soil after planting can destroy the stability of soil aggregates, breaking them up into very fine particles. Combined with insufficient organic matter, the soil packs together to form a crust on the surface, 0.2-5 cm thick. Usually occurring after a heavy rain, the crust causes water to puddle on the surface, but does not affect the structure of the soil below. Seedlings may be unable to break through the crust, resulting in delayed and sporadic crop emergence, leafing out below the crust, and stunted growth.

Prevent crusting

• Reduce or eliminate secondary tillage, or switch to a conservation tillage system
• Increase the amount of residue left on the soil surface after planting
• Include more legumes or grasses in the crop rotation
• Grow cover crops

Some other adverse effects of agricultural practices

• Irrigation can affect groundwater levels and concentrate salts in the soil
• Lower groundwater levels affect the growth of some trees with shallow root systems
• Monocultural practices can disperse varieties of beneficial birds and insects causing simplification of wildlife community structure.
• Since the habitat becomes less diversified, epidemics can create severe consequences on the survival of many species
• Sedimentation is the most damaging agent to aquatic systems
• Insecticides are lethal to aquatic invertebrates which are an integral part of the aquatic food chain
• Herbicides eliminate cover and feeding plants for fish and birds, and they can cause considerable damage to fish if allowed to reach a watercourse
• Plowed or bare soils discourage grassland birds
• Fence-to-fence cultivation of land eliminates edge rows of vegetation

(Wildlife and fish and sustainable agriculture, 1990)