Nitrogen supplied to corn by legumes in a Central Amazon Oxisol

Abstract

Two field studies with legume crop residues were conducted during three consecutive years in a Central Amazon Oxisol to determine their fertilizer-N substitution value and the influence of legume residue management on succeeding corn crops. In the first experiment, incorporated legume residues from two legume cover crops, mucuna (Mucuna aterrima (Piper & Tracy) Merr.) and indigofera (Indigofera tinctoria L.), and from cowpea (Vigna unguiculata (L.) Walp.) were compared each year with five different urea-N rates (0-160 kg N ha-1) with regard to their effect on yield and N accumulation by a succeeding corn crop. In the second experiment, legume residue management treatments, evaluated only with mucuna, were (1) incorporation; or (2) mulch of aboveground biomass produced in situ; (3) removal of aboveground biomass; and (4) incorporation of imported aboveground biomass to a bare plot. Mean fertilizer-N substitution value, during three consecutive years, was 74 kg ha-1 for mucuna and 26 kg ha-1 for indigofera and cowpea. Corn yields with incorporation of aboveground mucuna biomass exceeded the yields of the mulch treatment in only one of the three years.