College of Resources and Environmental Engineering, Yibin University, Yibin 644000, China;
U.S.Department of Agriculture, Agricultural Research Service, Forage and Range Research Laboratory, Utah State University,Logan, UT 84322-6300, USA;
U.S.Department of Agriculture, Agricultural Research Service, Forage and Range Research Laboratory, Utah State University,Logan, UT 84322-6300, USA;