EFFECT OF TILLAGE AND ROTATION ON AGRONOMIC PERFORMANCE OF CORN AND SOYBEAN - 20-YEAR STUDY ON DARK SILTY CLAY LOAM SOIL

In the U.S. Corn Belt, tillage without plowing was used on more than 5 0% of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] acreage in 1994, while no-till planting was used on about 30% of the acreage. Few research studies have evaluated these reduced tillage systems for 20 yr or more. This study includes plow, chisel, ridge, and no-till sy stems in continuous corn, corn after soybean, soybean after corn, and continuous soybean rotations. The experiment was conducted on Chalmers (fine-silty, mixed, mesic Typic Haplaquolls) silty clay loam soil in north-central Indiana for 20 yr. Objectives were to determine the effe ct of tillage and rotation on stands, growth, maturity, and yield of c orn and soybean and to determine trends that develop with time for the se variables. Major stand reductions occurred only in no-till continuo us corn, 8% less than plowing. Compared with plowing, chisel and ridge tillage systems reduced growth and yield and increased harvest moistu re by less than 3% in continuous corn. No-till reduced 4-wk height of continuous corn by 17%, yield by 14%, and increased harvest moisture b y 2.1 percentage points compared with plowing. For corn following soyb ean, only no-till corn showed a yield reduction, 2.8%, compared with p lowing. Twenty-year mean soybean yield reductions averaged 4 to 7% in both rotation and monoculture for chisel, ridge, and no-till systems c ompared with plowing. Relative yields for no-till continuous corn tend ed to be less than other tillage-rotation systems over time, while no- till soybean yields tended to improve with time, especially during the last 5 yr of the study. Both corn and soybean yields were better in r otation than in continuous cropping for all tillage systems. Of the ti llage systems-rotation combinations in this study, only no-till contin uous corn is likely to suffer major yield loss on a long-term basis on dark prairie soils of the Central and Northern Corn Belt.