Use of legume green manures as nitrogen sources for corn production.

摘要

Recent volatility in supplies and prices of natural gas and synthetic nitrogen (N) fertilizer suggests a need to develop and refine 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 m3 of natural gas. These types of savings are likely to become increasingly important as fossil energy supplies become scarcer and fertilizer prices rise.