Effects of soil erosion on crop productivity

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Abstract
Soil erosion and the effects of soil erosion on crop productivity have become emotional issues and have attracted the attention of agriculturists, environmentalists, and the public in general. In spite of heavy investments in research and development, the global rates of accelerated erosion are now presumbly higher than ever before. However, the data from available records obtained by diverse methods are uncomparable, unreliable, confusing, and often vary by several orders of magnitude. Reports of erosion‐caused alterations in crop productivity and soil properties are also contradictory and subjective. In addition to the lack of standardized methodology in evaluating soil erosion and its effects on crops, controversial interpretations are attributed to differences in soil profile characteristics, nutrient status, crops grown, and prevailing climatic conditions. Although erosion is generally associated wtih yield reductions, there are examples of where soil erosion has had no effect or has had a positive effect on crop production. Accelerated erosion affects productivity both directly and indirectly. Directly, the erosion‐induced reduction in crop yields is attributed to loss of rooting depth, degradation of soil structure, decrease in plant‐available water reserves, reduction in organic matter, and nutrient imbalance. Depending on soil properties and the degree of degradation, adverse effects of erosion on crop yields can be mostly compensated for by additional inputs of macronu‐trients (N, P, K) and macronutrients plus organic matter, by supplemental applications of some micronu‐trients, and by irrigation. For some soils, e.g., tropical soils, crop yields from severely eroded soils are significantly lower than those from uneroded lands and are often uneconomic in spite of additional inputs. Specific examples of yield alterations are given in relation to the loss of plant nutrients, soil water reserves, and alterations in soil properties. Criteria for soil‐loss tolerance are discussed, and productivity restoration of eroded soils is reviewed in relation to soil organic matter content and nutrient requirments. Research and development priorities are presented.