Soil erosion has both on-farm impacts (reduction in yield and farm income) and off-farm impacts (contaminated water due to the sediment and associated contamination from nutrients and pesticides carried on the soil particle).
On-farm impacts due to the loss of soil and nutrients include:
- lower fertility levels
- development of rills and gullies in the field
- poorer crop yields
- less water infiltration into the soil
- more soil crusting
- more runoff in the spring and after storms
When fertile topsoil is lost, nutrients and organic matter needed by crops often are removed along with it. Erosion tends to remove the less dense soil constituents such as organic matter, clays, and silts, which are often the most fertile part of the soil. However, the loss in productivity caused by erosion has not been so evident in many parts of the U.S., since it has been compensated for over the years by improved crop varieties and increased fertilization.
Soils can tolerate a certain amount of erosion without adverse effects on soil quality or long-term productivity, because new soil is constantly formed to replace lost soil. This tolerable level is known as "T" and generally ranges from 3 to 5 tons per acre per year. Goals for reducing soil erosion often use the "T" value as a target, because erosion rates below T should maintain long-term productivity of the soil.
Off-farm impacts occur when the eroded soil is deposited elsewhere, along with nutrients, pesticides or pathogens that may be attached to the soil. The tolerable"T" value described above does not take into consideration the off-farm or downstream impacts. Soil eroded by water has effects such as:
- eroded soil deposited in depressions and adjacent fields
- decreased water quality downstream
- decline of downstream aquatic ecosystems because of sedimentation and the addition of nutrients, pesticides, and bacteria associated with the soil
- clogged drainage ditches and other costly problems
Off-farm impacts of wind erosion are due to the blowing soil, which can reduce seedling survival and growth (seed cover), increase the susceptibility of plants to certain types of stress, contribute to transmission of some plant pathogens, and reduce crop yields. Dust affects air quality, obscures visibility which can cause automobile accidents, clogs machinery, and deposits in road ditches, where it can impact water quality.
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