Tolerable soil loss

A methodology was developed to estimate quantities of crop residues that can be removed while maintaining rain or wind erosion at less than or equal to the tolerable soil-loss level. Six com and wheat rotations in the 10 largest com-producing states were analyzed. Residue removal rates for each rotation were evaluated for conventional, mulch/reduced, and no-till field operations. The analyses indicated that potential removable maximum quantities range from nearly 5.5 million dry metric t/yr for a continuous corn rotation using conventional till in Kansas to more than 97 million dry metric t/yr for a corn-wheat rotation using no-till in Illinois. 

Index Entries Corn stover wheat straw rainfall erosion wind erosion tolerable soil loss. 

For each county in the 10 states evaluated, all cropland soil types in land capability classes (LCCs) I—VIII are identified. For each individual soil type, acres of that particular soil type, field topology characteristics (percentage low and high slopes), erodibility, and tolerable soil-loss limit are obtained from the USD A. These data are used in the rain and wind erosion equations described later. In each of the states analyzed, the following crop rotations are considered (where applicable) continuous corn, corn-soybean, corn-winter wheat, corn-spring wheat, continuous winter wheat, winter wheat-soybeans. 

To quantify the amount of residue that can be sustainably removed, quantities of residues that must be left on the field to maintain rain and/or wind erosion at or below tolerable soil-loss levels (T) must first be estimated. The revised universal soil loss equation (RUSLE) and the wind erosion equation (WEQ) are used to estimate these residue quantities (7,8). 

T, tolerable soil loss (Mg/[ha-yr]) Intercept Average Slope minimum residue remaining (dry Mg/[ha-yr])... 

Hall, G.F., R.B. Daniels, and J.E. Foss (1981). Rates of soil formation and renewal in the United States. In B.L. Schmidt, R.R. Allmaras, J.V. Mannering, and R.J. Papendick, eds., Determinants of Soil Loss Tolerance. Madison, WI American Society of Agronomy and Soil Science Society of America Special Publication. 45, pp. 23-29. 

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. 

Although arsenic is not an essential plant nutrient, small yield increases have sometimes been observed at low soil arsenic levels, especially for tolerant crops such as potatoes, com, rye, and wheat (Woolson 1975). Arsenic phytotoxicity of soils is reduced with increasing lime, organic matter, iron, zinc, and phosphates (NRCC 1978). In most soil systems, the chemistry of As becomes the chemistry of arsenate the estimated half-time of arsenic in soils is about 6.5 years, although losses of 60% in 3 years and 67% in 7 years have been reported (Woolson 1975). Additional research is warranted on the role of arsenic in crop production, and in nutrition, with special reference to essentiality for aquatic and terrestrial wildlife. 

The United Nation s report—prepared by over 1,000 scientists—predicts cultural and social disruptions, loss of wetlands, flooding of river deltas, bleaching of coral reefs, permafrost thawing, acidification of oceans, drop in crop output, widespread water shortage, and even starvation in parts of southern Europe, the Middle East, Africa, Mexico, Southern Asia, and the American Southwest. Deforestation, soil erosion, storms, droughts, and devastation of agriculture are likely to result as temperatures exceed the heat tolerance of crops. These trends can combine to cause migration, ethnic strife, social destabilization, and wars. 

Excess soil moisture is often more detrimental than a deficiency, especially in fine-textured soils. By making the soil anaerobic the root tissues are denied their essential supply of oxygen and many plant species will die very quickly, or at least be injured to such an extent that the crop is near a total loss. The sensitivity of plants varies widely rice, for example, thrives under submerged conditions but corn, tomatoes, and most other field and vegetable crops can tolerate a saturated soil for only a few hours, or at most a few days. 

Malenkov and Molotov why no one had tried to turn the area wholesale into agricultural production in the past. Crop yields therefore would be unpredictable from year to year with the potential for major losses of both grain and soil. Unpredictability, however, is not something that could be tolerated within the highly quantified realm of Soviet economic planning and its five-year plans, which called for firm quota assignments. Khmshchev evenmally would use this recalcitrance against both, but in the meantime, the foundations needed to be laid (Johnson et al., 1959 Linden, 1966 Timoshenko, 1932 Volin, 1970). 

---