Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/16/1996
Publication Date: N/A
Citation: Interpretive Summary: Moldboard plowing of agricultural fields, which completely buries crop residues and facilitates release of nitrogen from these residues for use by the next crop, is being replaced on corn and soybean acreage by reduced tillage systems. Reduced tillage systems have several advantages, including lower soil erosion, less surface crusting after hard rains, and better moisture conservation. Some farmers are diversifying their crop mix by adding a small grain, such as wheat, barley, or oats, to the rotation. In one reduced tillage system called ridge tillage, our research showed that including wheat in a corn-soybean rotation improved corn grain yield but required increased weed control efforts. An additional farming practice being adopted is to grow legume cover crops after small grains. These cover crops help reduce nutrient loss by leaching, add nitrogen to the soil, and protect the soil from wind and water erosion. Farmers need to know how much hnitrogen is made available to the next crop from these cover crops so they can add the correct amount of fertilizer nitrogen. Our research showed that two legume cover crop species, alfalfa and hairy vetch, did not provide a consistent amount of nitrogen to the next crop of corn. Farmers in the upper Midwest using ridge tillage may be encouraged to consider diversifying their corn-soybean rotations by adding a small grain but should not depend on legume cover crops after wheat to provide nitrogen to the following corn crop.
Technical Abstract: Information is scant on the response of corn (Zea mays L.) following legumes seeded with small grains in reduced tillage systems in the upper Midwest. Our objective was to determine yield and N uptake response of strip-intercropped corn planted after soybean [Glycine max (L.) Merr], wheat (Triticum aestivum L.) alone, wheat with alfalfa (Medicago sativa L.), or wheat with hairy vetch (Vicia villosa Roth) compared to continuous corn. Field studies were conducted from 1991 through 1994 at two southern Minnesota locations on poorly drained Webster clay loam soils (Typic Haplaquolls) in a ridge-tillage system. Averaged across years at Freeborn, corn grain yield in the wheat plus legume rotations was 1.3 Mg/ha more than continuous corn and was equal to that in a wheat alone rotation at fertilizer N rates up to 135 kg N/ha. Grain yield of corn in the rotation with soybean was 2.1 Mg/ha more than continuous corn. Aboveground biomass of corn in the three wheat rotations accumulated 17 kg/ha more N than continuous corn up to N rates of 135 kg N/ha. At Waseca, grain yield and total N uptake of corn grown in the wheat plus legume rotations were 1.5 Mg/ha and 17 kg N/ha more, respectively, than in the wheat alone rotation and were equal to those from the rotation with soybean and continuous corn at N rates up to 135 kg N/ha. Regression analysis indicated that significant, positive, non-N-related rotation effects were present at Freeborn but not at Waseca. Based on our findings, we cannot recommend inclusion of annual alfalfa or hairy vetch with wheat in a ridge-tillage system because they do not provide a consistent source of available N for the subsequent corn.