1. Soil and Crop Sciences Dep. Texas A&M Univ. College Station TX 77843 USA
2. Texas A&M AgriLife Research Hwy 59 E Beeville TX 78102 USA
3. Dep. of Crop and Soil Sciences Washington State Univ. Pullman WA 99164 USA
4. Texas A&M AgriLife Research and Extension Center Lubbock TX 79403 USA
5. Dep. of Ecology and Conservation Biology Texas A&M Univ. College Station TX 77843 USA