Summary and Keywords
Soil erosion by water is a natural process that cannot be avoided. Soil erosion depends on many factors, and a distinction should be made between humanly unchangeable (e.g., rainfall) and modifiable (e.g., length of the field) soil erosion factors. Soil erosion has both on-site and off-site effects. Soil conservation tries to combine modifiable factors so as to maintain erosion in an area of interest to an acceptable level. Strategies to control soil erosion have to be adapted to the desired land use. Knowledge of soil loss tolerance, T, i.e., the maximum admissible erosion from a given field, allows technicians or farmers to establish whether soil conservation practices need to be applied to a certain area or not. Accurate evaluation of the tolerable soil erosion level for an area of interest is crucial for choosing effective practices to mitigate this phenomenon. Excessively stringent standards for T would imply over expenditure of natural, financial, and labor resources. Excessively high T values may lead to excessive soil erosion and hence decline of soil fertility and productivity and to soil degradation. In this last case, less money is probably spent for soil conservation, but ineffectively. Basic principles to control erosion for different land uses include maintaining vegetative and ground cover, incorporating biomass into the soil, minimizing soil disturbance, increasing infiltration, and avoiding long field lengths. Preference is generally given to agronomic measures as compared with mechanical measures since the former ones reduce raindrop impact, increase infiltration, and reduce runoff volumes and water velocities. Agronomic measures for soil erosion control include choice of crops and crop rotation, applied tillage practices, and use of fertilizers and amendments. Mechanical measures include contour, ridging, and terracing. These measures cannot prevent detachment of soil particles, but they counter sediment transport downhill and can be unavoidable in certain circumstances, at least to supplement agronomic measures. Simple methods can be applied to approximately predict the effect of a given soil conservation measure on soil loss for an area of interest. In particular, the simplest way to quantitatively predict mitigation of soil erosion due to a particular conservation method makes use of the Universal Soil Loss Equation (USLE). Despite its empirical nature, this model still appears to represent the best compromise between reliability of the predictions and simplicity in terms of input data, which are generally very difficult to obtain for other soil erosion prediction models. Soil erosion must be controlled soon after burning.
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