1. Dep. of Biosystems Engineering and Soil Science The Univ. of Tennessee Knoxville TN 37996 USA
2. USDA‐ARS Central Great Plains Research Station Akron CO 80720 USA
3. Office of Information Technology The Univ. of Tennessee Knoxville TN 37996 USA
4. Dep. of Agronomy and Horticulture Univ. of Nebraska Lincoln NE 68588 USA