Sunflower‐Soybean and Grain Sorghum‐Corn Rotations Versus Monoculture 1

Crop alternation was compared with continuous cropping for sunflowers and soybeans and for grain sorghum and corn at Rosemount, Minnesota. No fertilizer was used in order that full effect of crop removal could be observed. Yields from crop alternations of corn‐sorghum or sunflower‐soybeans exceeded those from continuous cropping. Sunflower‐soybean alternation was superior to continuous sunflower in sunflower disease control. Soybeans in a corn or sorghum sequence greatly increased yields of the feed grains. Differences between sunflowers and soybeans and between sorghum and corn in effect on soil pH and depletion of acid‐soluble P and K were small and unimportant. Verticillium albo‐atrum on sunflowers increased during the study and became the major factor affecting yield. The benefit of rotation in delaying the appearance of the disease was evident even though one might expect spread of inoculum from plot to plot by tillage practices. No other disease or insect problem was observed as a result of continuous cropping of plots to sunflowers, soybeans, grain sorghum, or corn.