ARS | Publication request: Long-term assessment of runoff and sediment transport from grass and agroforestry buffers in corn/soybean watersheds using APEX

Submitted to: North American Agroforestry Conference
Publication Type: Abstract Only
Publication Acceptance Date: November 16, 2011
Publication Date: June 4, 2011
Citation: Senaviratne, A., Anderson, S.H., Udawatta, R.P., Baffaut, C. 2011. Long-term assessment of runoff and sediment transport from grass and agroforestry buffers in corn/soybean watersheds using APEX [abstract]. North American Agroforestry Conference, June 4-9, 2011, Atlanta, GA. 52.

Technical Abstract: Existence of a claypan layer in soils at depths ranging from 4 to 37 cm restricts water movement and has contributed significantly to high rates of runoff, sediment transport, and other non-point source loadings from croplands in watersheds. The deposition of these pollutants in rivers, streams and lakes has left more than half of them impaired with degraded water and damaged eco-systems. A study conducted evaluating grass and agroforestry buffers in corn (Zea mays)-soybean (Glycine max) watersheds over a period of 19 years have shown significant reductions in runoff, sediment, and nutrient loadings compared to a control watershed. The present study aimed to investigate the specific effects of grass and agroforestry buffers for optimum benefits in runoff and sediment reductions from the watersheds through simulations using the Agricultural Policy Environmental eXtender (APEX) model. The APEX model was calibrated and validated for runoff with measured data with coefficients of determinations (r2) ranging from 0.84 to 0.89, respectively. The r2 values for calibration and validation of the model for sediment transport were 0.65 and 0.66, respectively. The calibrated and validated model was used to simulate 20 years of runoff and sediment transport. The inclusion of agroforestry buffers showed a 25 percent reduction in sediment yield and an 8% reduction in runoff compared with the control watershed. The APEX model appears to reasonably simulate the watersheds with agroforestry and grass buffers; however, there is a need to upgrade for specific tree species within the buffers which is currently absent in the model. The upgraded model is anticipated to predict long-term benefits, buffer configurations, and placement of buffers for maximum reductions of runoff, sediments and nutrients.