Soil erosion reduction, Conservation

Conservation agroecosystems developed in the Great Plains of the U.S. to control soil erosion are characterized by the presence of varying quantities of plant residues on the soil surface. This residue mulch protects the soil from the erosive forces of wind and water, resulting in improved stream water quality and soil conservation. Conservation tillage systems also help maintain soil productivity and reduce energy requirements of crop production (15). However, crop yield reduction has been observed with conservation wheat production in some areas of the U.S. (16-18) and with rice culture in the Far East (, 20). 

Conservation tillage and no-till often produce dramatic decreases in water runoff and increases in water infiltration, which results in a reduction not only in soil erosion, but also in pesticide and nutrient runoff into water (Glenn and Angle, 1987 Hall et al, 1991). In several studies of best management practices (BMPs), no-till was shown to reduce herbicide runoff by an average of 70%, while ridge till showed a 40% reduction (Figure 1.7). 

Because soil sediment has an extremely negative impact on streams, rivers, and lakes, erosion reductions credited to conservation tillage provide major benefits to aquatic ecosystems. Additionally, conservation tillage benefits wildlife by providing more crop residues for cover, more food sources (grain and weed seed left on the soil surface, as well as a greater number and variety of invertebrates), and less field disturbance. 

Conservation tillage is one of the most practical and economical ways to reduce soil erosion. Surface crop residue protects the soil from the erosive impacts of wind and rain. Reductions in erosion are proportional to the soil coverage of crop residue. From 78% to 89% of the variance in erosion between tillage systems is explained by the percentage of soil coverage by plant residue (Laflen el al, 1978). No-till systems, which leave nearly all surface plant residue in place, usually reduce erosion by 90% or more. 

Solutions of the equation provide alternate plans wherein the annual soil loss from a specific field can be held within the limits that can be tolerated under the soil topographic conditions involved. In spite of the fact that nearly 15 X 10 has been spent on soil conservation in the U.S.A. since the mid-1930 s, soil erosion remains one of the biggest and most pervasive problems still facing the nation (Carter, 1977). The dust storms that occurred in early 1977 underline this statement. Nationally, erosion losses have been estimated at about 2.5 kg m" each year, but soil scientists believe that even deep soils cannot sustain a fraction of this loss within serious reductions in productivity. Discounting erosion losses, top soil possibly forms at the rate of about 0.35 kg m" y in humid regions. 

Like the Piedmont, much of the present forest extending from Texas to Maine is old cropland which has reverted to forest and much of that has occurred over the past 70 or so years (McCleery, 1992). The effect of cropland reversion plus soil conservation measures on the remaining Piedmont cropland was to greatly reduce erosive land use and thus to reduce erosion to very low levels. The sea of forest shown in Fig. 77.6 is has significance far beyond reduction of soil erosion. First, it has been a huge carbon sink as the forest grows and as more carbon is incorporated into the soil. No exact values are available but North American forests contain about 170 billion tons of carbon (SOCCR, 2007). The second effect is that this reversion... 

Trimble, S. W, Lund, S. (1982). Soil conservation and the reduction of erosion and sedimentation in the Coon Creek basin, Wisconsin. USGS Professional Paper 1234. 

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