MINERALIZATION AND CORN RECOVERY OF 15NITROGEN FROM BLACK OATS RESIDUES TREATED WITH HERBICIDES

Nitrogen (N) mineralization from black oat residues (Avena strigosa), with or without previous application of herbicides, and its utilization by corn crop were investigated. The experiments were performed in a completely randomized setup, with three treatments and ten replicates. The treatments were: A) control - corn grown in soil with residues of black oats harvested without herbicide application; B) glyphosate - corn grown in soil with residues of glyphosate-desiccated black oat; and C) glufosinate - corn grown in soil with residues of black oat previously desiccated with glufosinate-ammonium. The remaining black oat residues on the soil surface were smaller in the control treatment than in glyphosate and glufosinate treatments. Black oat residues from the control treatment released 30% and 20% more carbon (C) and nitrogen (N), respectively, than from herbicide treatments. Microbial biomass carbon, total and mineral soil N arising from black oat residues were reduced by herbicide management. Black oat residues treated with glyphosate reduced corn total-N by 16%; however, dry mass yield was not affected by the treatments. Herbicide application on black oat reduced the total amount of residue-released nitrogen in the corn kernels, leaves and the whole plant. Net nitrogen mineralization from black oat residues is affected by the application of glyphosate or glufosinate-ammonium.