An Improved Representation of Vegetative Filter Strips in SWAT

Vegetative filter strips (VFS) are popular conservation practices installed at the edges of agricultural fields to reduce losses of pollutants from agricultural areas to receiving waterbodies. The recent interest in using VFS areas as multifunctional landscapes necessitates an improved depiction of VFS in simulation models. This study is aimed to enhance the physical representation of VFS in the Soil and Water Assessment Tool (SWAT) to improve the representation of ecohydrologic processes and land management practices in VFS areas. The proposed enhancement enables routing of water, sediment, and nutrients from the source area through the VFS area and makes the infiltrated water and nutrients available for filter crop uptake. The improvements are implemented in SWAT by modifying input files through Matlab scripts and by changing SWAT subroutines to enable routing. The model improvements are tested with three paired watershed studies with and without edge-of-field VFS in central Iowa. The improved model estimated 46% runoff reduction, 91% sediment reduction, 83% total phosphorus reduction, and 54% nitrate reduction with VFS, and these estimates closely matched the measured VFS reductions. The improved model was able to represent increased infiltration, soil moisture, and denitrification in the VFS area, along with accurately capturing crop yields in the source and VFS areas. Overall, the results indicate improved physical representation of VFS in SWAT.This article is published as Cibin, Raj, Indrajeet Chaubey, Matthew J. Helmers, K. P. Sudheer, Michael J. White, and Jeffrey G. Arnold. "An improved representation of vegetative filter strips in SWAT." Transactions of the ASABE 61, no. 3 (2018): 1017-1024. DOI: 10.13031/trans.12661. Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted

Impacts of Federal Crop Insurance on Land Use and Environmental Quality

This paper integrates economic and physical models to assess how federal crop revenue insurance programs might affect land use, cropping systems, and environmental quality in the U.S. Corn Belt region. The empirical framework includes econometric models that predict land conversion, crop choices, and crop rotations at the parcel-level based on expectation and variance of crop revenues, land quality, climate conditions, and physical characteristics at each site. The predictions are then combined with site-specific environmental production functions to determine the effect of revenue insurance on nitrate runoff and leaching, soil water and wind erosion, and carbon sequestration. Results suggest that crop insurance will have small impacts on conversions of non-cropland to cropland, and somewhat more significant impacts on crop choice. These changes in crop mix have small impacts on agricultural pollution