ABSTRACT:
Use of legumes, such as alfalfa, in cropping systems is often recommended as a means of reducing or eliminating nitrate pollution from agriculture. We analyzed literature that supports this recommendation and used published estimates to calculate the net input of N2 fixed by alfalfa to the agricultural N cycle in the Corn Belt. Although alfalfa occupies only 8% of the cropland, it fixes more than 1 billion kg N annually, compared to 4 billion kg fertilizer N applied to all crops in the eight-state region. Alfalfa can contribute symbiotically fixed N2 to soil both directly, through mineralization of plant residues and accretion from growing plants, and indirectly, through the recycling of manure porn animals fed alfalfa. Producers often fail to reduce N applications on corn planted after alfalfa after manure application. Our calculations demonstrate that the amount of fertilizer N applied to corn could be reduced by as much as 14% without reducing yields.
Footnotes
T. A. Peterson and M. P. Russelle are soil scientists with the Plant Science Research Unit, Dairy Forage Research Center (Minnesota Cluster location), Agricultural Research Service, U.S. Department of Agriculture, and the Soil Science Department, 439 Borlaug Hall, University of Minnesota, St. Paul, 55108. 7% article is a joint contribution from USDA-11RS and the Minnesota Agricultural Experiment Stcrrron, paper no. 18162 of the Scientific Journal Series. We thank many state and federal forage specialists for their assistance, several people who provided excellent peer reviews of an earlier draft, and Dr. R. H. Rust who provided the estimates necessary to develop the maps in figure 1.
- Copyright 1991 by the Soil and Water Conservation Society
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