EFFECT OF IRRIGATED CROP ROTATIONS ON YIELD AND SOIL FERTILITY

Abstract

Crop yields and soil analyses were compared from three 4-year, two 5-year, and two 7-year rotations. The yields of potatoes from the seven rotations were not significantly different. Barley was grown in six rotations and the yields from these were not significantly different. The yield of sugar beets from the one rotation that did not receive any manure was significantly lower than those from the other six rotations. In the rotation in which sweet corn followed sweet clover green manure the yields were significantly lower than those from the other six rotations, where the corn followed sugar beets. This presumably was a result of the phytotoxicity of the decomposing clover. Good husbandry practices such as manure and fertilizer application evidently overshadow the effect of rotations on the yields of irrigated crops. The organic matter and nitrogen of the surface 6 in. of soil were maintained in the rotations that included 3 years of alfalfa or alfalfa–brome mixture. These soil constituents were not maintained with a single year of alfalfa or with a partial green manure crop.