INTEGRATED ASSESSMENT AND ANALYSIS OF PHYSICAL LANDSCAPE PROCESSES THAT IMPACT THE QUALITY AND MANAGEMENT OF AGRICULTURAL WATERSHEDS
Location: Watershed Physical Processes Research Unit
Title: Modeling Landscape Evolution Due to Tillage
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2008
Publication Date: February 1, 2009
Citation: Vieira, D.A., Dabney, S.M. 2009. Modeling Landscape Evolution Due to Tillage. Transactions of the ASABE. 52:1505-1522.
Interpretive Summary: Tillage erosion results from soil movement caused by farm implements. After years of repeated operations, tillage creates areas of erosion and deposition within agricultural fields. The amounts of erosion can be significant, contributing to the modification of the land surface. Tillage causes redistribution of soil chemicals and nutrients that are important to plant growth and affects the thickness of topsoil, which can cause reduction in crop yields in parts of the fields. Despite its detrimental effects, tillage erosion is rarely considered in the estimation of erosion for conservation planning.
A computer model has been developed to predict the locations and amounts of erosion and deposition caused by tillage. The model determines where and how fast erosion takes place. For a given field topography and a record of tillage operations, the model can compute how erosion develops through the years. The model has been fully tested and applied to a field near Coffeeville, Mississippi, where the long-term effects of tillage erosion have been studied for more 12 years.
Simulations conducted with the newly developed model can provide valuable information to NRCS field offices personnel, who can identify problem areas within a field, evaluate the performance of alternative practices, and ultimately prescribe remedial measures that will help maintain crop productivity.
Tillage erosion has been identified as an important contributor to the modification of agricultural landscapes, especially in areas near field borders, vegetative barriers, and other features that usually induce localized erosion or soil accumulation. A two-dimensional, grid-based model has been developed to compute soil redistribution and morphological changes of complex landscapes due to tillage operations. Soil movement along and perpendicular to the directions of tractor movement are computed as a function of local slope gradients and of characteristics of the tillage implement.
A control volume approach is employed to determine terrain elevation changes after each tillage pass. The model explicitly considers the presence of internal and external field boundaries, simulating their influence on the development of erosion and deposition patterns. GIS layers are used to provide terrain elevation data, actual tillage directions, field borders, and the location of other features, such as vegetated strips, trees, or fences.
The model has been applied to an experimental field in Coffeeville, Mississippi, where grass hedges were planted close to field elevation contours to evaluate their effectiveness as an erosion control measure, and to investigate the formation of landscape benching. The model correctly reproduced the location and magnitude of aggradation and degradation areas over a 12-year period. Soil redistribution due to tillage is comparable to field observations that showed erosion averaging 20 cm occurred in the downslope side of each vegetative strip and deposition taking place upslope of them. The net result was a reduction from 7% to 5% in the average grade of the tilled areas between the hedges.