Submitted to: Water Erosion Prediction Project Documentation
Publication Type: Book / Chapter
Publication Acceptance Date: August 1, 1995
Publication Date: N/A
Interpretive Summary: Water erosion is a problem on many soils. WEPP is an erosion model designed to predict the loss of sediment and the amount of runoff from water erosion due to land management practices, variations in landscape and soil type, and differing climatic conditions. WEPP includes a submodel that will predict the amount of plant residue on the soil surface at any given time. This is especially important since one of the most cost- efficient ways to protect soil against water and wind erosion is to surface manage the crop residues. Over 75% of the soil conservation compliance plans required by the 1985 Farm Bill include residue management as a component of the erosion control measures. The successful adoption of surface residue management systems will partially depend on knowledge of how rapidly surface managed crop residues are broken down and lost from the field site. Such information is needed to determine the amount of residue cover present on a field during critical erosion periods and to aid the design of management practices that will optimize the benefits of crop residues remaining on the soil surface. The residue decomposition and management component of WEPP accounts for changes in the amount of residue present above, on, and below the soil surface. Within this model, residue decomposition is controlled by soil structural characteristics and climatic conditions such temperature and precipitation. Microbial population and nutrient cycling impacts are not considered because there is insufficient knowledge regarding the processes involved. The plant and residue management options available include: herbicide application, silage removal, tillage, shredding, burning, or removing residue, hay harvesting, and livestock grazing. Rangeland applications are also discussed.
Technical Abstract: WEPP includes a submodel that will predict the amount of plant residue on the soil surface at any given time. This is especially important since one of the most cost-efficient ways to protect soil against water and wind erosion is to surface manage the crop residues. Over 75% of the soil conservation compliance plans required by the 1985 Farm Bill include residue management as a component of the erosion control measures. The submodel simulates the decomposition of standing and flat plant residues, as well as the roots and buried residues in the surface 0.15 m of the soil profile. In the field, residue decomposition rates are controlled by environmental factors. Especially important are the water content and temperature. The effects of water content and temperature on the rate of residue decomposition were assumed to be independent of one another. To model the influence of these factors on residue decomposition, the optimum decomposition rate during a 24 hr period for a given residue type is modified by the actual temperature and available water present. The model also simulates the amount of the soil surface covered by the standing and flat residues. The cropland section can accommodate fallow, mono, double, rotation, strip, and mixed cropping practices. A mixed cropping practice is one where two or more individual cropping practices (e.g. mono and double) are used in the simulation. Standing residues are converted to flat residues due to decomposition, tillage and other management operations, wind and snow. Flat residues are lost form the surface due to decomposition and burial by management operations. The rangeland section contains the management options for livestock grazing, burning, and herbicide application.