NITROGEN FROM LEGUME COVER CROPS FOR NO-TILLAGE CORN

Many of the advantages of no-tillage crop production are due to the presence of a mulch from a cover crop or from crop residue. Legumes can be used to provide the mulch and biologically fixed N to nonlegumes in the system. Field experiments were conducted from 1977-1981 to determine the amount of biologically fixed N provided to no-tillage corn (Z. mays L.) by winter annual legume cover crops of hairy vetch (Vicia villosa Roth), big flower vetch (V. grandiflora W. Koch var. kitailbeliana) and crimson clover (Trifolium incarnatum L.). The legumes were compared to a cover of corn residue only and a cover crop of rye (Secale cereale L.). The soil was a Maury silt loam (Typic Paleudalfs, fine-silty, mixed, mesic). Fertilizer N treatments of 0, 50 and 100 kg ha-1 were combined with each cover treatment. Corn was planted by no-tillage directly into the cover treatments and the cover crops were killed with herbicides. Hairy vetch produced more dry matter with a higher N percentage which resulted in a higher N concentration in corn plants and substantially more inorganic N (KCl extractable NH4+ and NO3-) in the soil than with the other legumes. Big flower vetch and crimson clover provided much less N than hairy vetch. Five-year average yields of corn grain following hairy vetch cover crop with no N fertilizer were about 2.5 Mg ha-1 more than corn yields, when following corn residue or rye cover crop. It is estimated that hairy vetch supplied biologically fixed N equivalent to approximately 90-100 kg ha-1 fertilizer N annually to the corn, based on a comparison of grain yields with corn grown in corn residue and rye. In addition to functioning as an effective mulch, certain legume cover crops can provide a substantial portion of the N for no-tillage corn production, decreasing the amount of N fertilizer needed.