ENHANCED MIDWESTERN CROPPING SYSTEMS FOR SUSTAINABILITY AND ENVIRONMENTAL QUALITY
Location: Agroecosystems Management Research Unit
Title: Use of legume manures as nitrogen sources for corn production
Submitted to: Renewable Agriculture and Food Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 16, 2011
Publication Date: August 5, 2011
Citation: Liebman, M., Graef, R., Nettleton, D., Cambardella, C.A. 2011. Use of legume manures as nitrogen sources for corn production. Renewable Agriculture and Food Systems. p. 1-12. Available: http://dx.doi.org/10.1017/S1742170511000299.
Interpretive Summary: Nitrogen (N) fertility is important for corn production. Within the United States, more N fertilizer is applied to corn than to any other crop. Production of synthetic N fertilizer requires large quantities of fossil fuel energy. The price and availability of synthetic N fertilizer depends on expensive fossil fuel inputs, resulting in additional economic risk to the farmer. Adopting alternative strategies for supplying N to corn that rely on ecological processes rather than industrial processes may help reduce the risk associated with corn production. We grew red clover or alfalfa intercropped with oat as green manures for corn production and found that the fossil fuel energy savings accrued by intercropping legumes with oats to supply N for corn production is equivalent to the energy content of 104 to 274 cubic meters of natural gas. These types of savings are likely to become more important as fossil energy supplies become scarcer and fertilizer prices rise. This information will be useful to scientists, farmers, and public and private organizations who are interested in economically viable ecologically-based N fertility strategies for corn production.
Recent volatility in supplies and prices of natural gas and synthetic N fertilizer suggests a need to develop and refine alternative strategies for supplying N to corn. In this study, conducted in northeastern Iowa, we examined the use of red clover and alfalfa green manures as means of supplying N to a succeeding corn crop. Red clover intercropped with oat produced significantly more biomass and contained more N than alfalfa intercropped with oat. Fall or spring tillage did not have a consistent effect on green manure N content. Without N fertilizer, corn grain yield following oat-red clover and oat-alfalfa was 25 to 63% greater than following oat grown alone, but at the highest fertilizer rate (202 kg N ha-1), there was no difference in corn yield between oat-legume and oat-alone treatments. These patterns support the premise that legume green manure effects on corn yield were N-related. Red clover green manure had an N fertilizer replacement value for corn of 87 to 184 kg N ha-1; alfalfa supplied corn with the equivalent of 70 to 121 kg N ha-1. At a fossil energy cost for N fertilizer of 57 MJ kg-1 N, reducing synthetic N fertilizer applications to corn by 70 to 184 kg N ha-1 would represent a fossil fuel savings of 3,990 to 10,488 MJ ha-1, equivalent to the energy content of 104 to 274 m3 of natural gas. These types of savings are likely to become increasingly important as fossil energy supplies become scarcer and fertilizer prices rise.