1. USDA‐ARS Soil and Water Conservation Research Adams OR 97810 USA
2. School of Economic, Political and Policy Sciences Univ. of Texas at Dallas Richardson TX 75080‐3021 USA
3. Dep. of Crop and Soil Sciences Univ. of Georgia Tifton GA 31794 USA
4. Dep. of Agronomy, Horticulture and Plant Science Univ. of South Dakota Brookings SD 57007 USA