YIELD AND NITROGEN UPTAKE OF ROTATED CORN IN A RIDGE-TILLAGE SYSTEM

Information is scant on the response of corn (Zea mays L.) following l egumes seeded with small grains in reduced tillage systems in the uppe r Midwest, Our objective was to determine yield and N uptake response of ridge-tilled corn planted after soybean [Glycine max (L.) Merr.], w heat (Triticum aestivum L.) alone, wheat with alfalfa (Medicago saliva L.), or wheat with hairy vetch (Vicia villosa Roth), compared with co ntinuous corn. Field studies were conducted from 1991 through 1994 at two southern Minnesota locations on a poorly drained Webster clay loam (fine-loamy, mixed, mesic Typic Endoaquoll) soil. At Freeborn, corn g rown in rotation with soybean yielded highest (6.8 Mg ha(-1)) in 2 of 3 yr, while continuous corn usually yielded less than corn grown after other crops. Corn grown after other crops accumulated 23 to 36 kg ha( -1) more N than continuous corn in 2 of 3 yr at all fertilizer-N rates up to 135 kg N ha(-1). At Waseca, corn grain yields and N uptake were generally similar among rotations, except that yields were 1.5 to 1.9 Mg ha(-1) lower and total N uptake was 16 to 18 kg ha(-1) less follow ing wheat alone in 2 of 3 yr, compared with other rotations at fertili zer-N rates up to 135 kg N ha(-1). Regression analysis indicated that significant, positive, non-N-related rotation effects were present at Freeborn, but not at Waseca, where there was a negative effect of whea t alone on subsequent corn yield. The potential fertilizer-N savings d ue to including annual alfalfa or hairy vetch could not be calculated because the N rates used in this study were insufficient to determine the economically optimum N rate. However, neither the alfalfa nor hair y vetch provided a consistent source of available N for the subsequent corn crop in this study.