1. Department of Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
2. Department of Natural Resources Science, University of Rhode Island, Kingston, RI 02881, USA
3. Department of Environmental Science and Technology, University of Maryland, College Park, MD 20740, USA
4. Department of Agronomy, Kansas State University, Manhattan, KS 66506, USA