It is now believed that a major reason for frequently observed decline in alfalfa seed yields after the first or second year has been the lack of sufficient subsoil moisture. In deep alluvial soils (for the first crop or two) the subsoil moisture present is generally a carryover from previous crops—if they were shallow rooted, or were irrigated late in the season. These test results show that 48 inches of irrigation water, applied to a dry soil, is sufficient moisture to insure production of a good alfalfa seed crop.