Fig. 1. USDA on-farm alfalfa yield (Mg ha-1) from 1919 to 2000 for the USA and upper Midwest and northern Great Plains (USDA, 2001).
Fig. 1. USDA on-farm alfalfa yield (Mg ha-1) from 1919 to 2000 for the USA and upper Midwest and northern Great Plains (USDA, 2001).