ENVIRONMENT AFFECTS THE CORN AND SOYBEAN ROTATION EFFECT

Corn (Zea mays L.) and soybean [Glycine mar (L.) Merr.], the backbone of Midwestern crop production, respond to rotation, but how growing co nditions affect this is not well documented. Our objectives were to de termine the effect of various corn and soybean cropping patterns on yi elds and to evaluate environmental effects on the rotation effect. The study began in 1981 at Lamberton, MN, on a Webster clay loam (fine-lo amy, mixed, mesic Typic Endoaquoll), in 1982 at Waseca, MN, on a Nicol let clay loam (fine-loamy, mixed, mesic Aquic Hapludoll), and in 1983 at Arlington, WI, on a Piano silt loam (fine-silty, mixed, mesic Typic Argiudoll). Cropping sequences were (i) continuous monoculture of eac h crop; (ii) annual rotation of the two crops; and (iii) 1, 2, 3, 4 an d 5 yr of each crop following 5 yr of the other crop. Results are base d on 11 yr Of data at Lamberton, 8 yr (soybean) or 9 yr (corn) at Wase ca, and 9 yr at Arlington. Corn rotated annually with soybean yielded 13% more, and 1st-yr corn following multiple years of soybean yielded 15% more than continuous corn. Soybean annually rotated with corn yiel ded 10% more, and 1st-yr soybean following multiple years of corn yiel ded 18% more than continuous soybean. The crops differed in response t o increasing years of consecutive planting: 2nd-yr to 5th-yr corn yiel ds were no different from continuous corn yields; 2nd-yr soybean yield ed 8% more than continuous soybean, 3rd-yr soybean yielded 3% more, an d 4th- and 5th-yr soybean yielded the same as continuous soybean. Rela tive increase in yields of both crops in annual rotation compared with monoculture was approximately twofold greater in low-yielding than in high-yielding environments. In low-yielding environments, the yield a dvantage of an annual rotation of corn and soybean compared with monoc ulture was frequently greater than 25%. The commonly practiced annual rotation of corn and soybean maximized corn yields, but not soybean yi elds, relative to the other sequences studied.