Use of legume green manures as nitrogen sources for corn production
2012
Liebman, Matt | Graef, Rhonda L. | Nettleton, Daniel | Cambardella, Cynthia
Recent volatility in supplies and prices of natural gas and synthetic nitrogen (N) fertilizer suggests a need to develop andrefine alternative strategies for supplying N to corn. In this study, conducted in north-eastern 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. Tilling green manures in the fall or delaying tillage until the following spring 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 25–63% 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 87–184 kg N ha (-1) ; alfalfa supplied corn with the equivalent of 70–121 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 70–184 kg N ha (-1) would represent a fossil fuel savings of 3990–10,488 MJ ha (- )1 , equivalent to the energy content of 104–274 m 3 of natural gas. These types of savings are likely to become increasingly important as fossil energy supplies become scarcer and fertilizer prices rise.
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