The use of winter annual legume cover crops in a wheat-grain sorghum rotation in south central Kansas

Winter annual legumes in humid regions of the country can have a positive effect on subsequent corn (Zea mays) and grain sorghum (Sorghum bicolor) crops, mainly through N contribution of the legume and, in some cases, soil improvement. However, water use by the cover crop in drier regions has the potential to reduce yields in subsequent crops. This study was initiated in central and south-central Kansas to look at both the agronomic and economic implications of adding a winter annual legume cover crop to a winter wheat (Triticum aestivum)grain sorghum rotation. Experiments included researcher-managed onstation trials and cooperative (i.e., fanner-managed) trials with farmers using hairy vetch (Vicia villosa) and Austrian winter pea (Pisum arvense). Results showed that in good rainfall years, establishment of cover crop was adequate, and no significant difference occurred between sorghum yields following cover crops versus following wheat with fertilization. On-station trials showed a significant nitrogen (N) contribution from hairy vetch and benefits to sorghum. During years with low rainfall, cover crop establishment was poor, N contribution from the cover crop was low, and grain sorghum yields were reduced because of water use by the cover crop. Variable costs were similar between cover crop and fertilized treatments, but gross returns and, consequently, net returns were lower in the cover crop plots because of this yield reduction. For cover crops to be attractive options for farmers in this part of Kansas: they must be used also for livestock feed and/or for early spring grazing; other cultivars or management systems that use less water must be developed; experiments must be conducted to ascertain benefits of cover crops during the second rotation cycle; and the price of N fertilizer must increase to the point that use of alternative sources is economical. Also, the use of cover crops by farmers in regions of variable rainfall should not be "recipe driven" but "response driven," using cover crops in years where rainfall is adequate, and not planting or destroying stands during dry years to conserve water for the cash crop.