WATER TABLE AND IRRIGATIONEFFECTS ON ALFALFAGROWNON SANDY SOILS

The effects of water table depths and irrigation levels on production of alfalfa, Medicago sativa L., were evaluated and compared in field-plot and field-lysimeter studies on sandy soils in North Dakota. The two experiments were not conducted simultaneously. Water table depths dropped seasonally in the field-plot experiment but were kept constant in the lysimeter experiment. The field-plot experiment had three water table depths with four irrigation levels; the lysimeter experiment had four water table depths with three irrigation levels. For the field-plot experiment, yields over 2 yr were highest with seasonal average shallow water tables of 1.2 and 1.7 m, regardless of irrigation, and irrigation increased yields significantly with the deepest watertable (2.3 m). During the second year, yields of 2 tonne/ha higher occurred. For the lysimeters, yields over 2 yr were significantly depressed with the 46-cm water table and consistently high yields were obtained with the 155-cm water table. Thus, water table depth significantly affects yield of irrigated alfalfa grown on sandy soils in the northern Great Plains and the optimum water table depth for maximum alfalfa production is between 1 and 2 m.