Balance de nitrógeno en maíz forrajero con diferente fertilización y fase de rotación con praderas

the aim of this study ivas to evaluate the nitrogen (n) balance in soil during a crop cycle of forage maize (zea mays l.), in different phases of a rotation with pastures (pu) and with different rates of n fertilization (nf). nine treatments derived from the combination of two factors with three levels each were evaluated: 1) nf: 0 (n0), 100 (n100) and 200 (n200) kg n ha-1; and 2) pu: three and a half years of alfalfa (medicago sativa l.) associated with orchardgrass (dactylis glomerata l.) (p); three years of alfalfa associated with orchardgrass and a cycle of oats (avena sativa l.) associated with ryegrass (lolium multiflorum lam.) (pa); and two and a half years of alfalfa associated with orchardgrass, a cycle of maize and a cycle of oats associated with ryegrass (pma). the experimental design was split-plots in a randomized block design with three repetitions with up as a large plot and nf as a small plot. measurements included n extraction by the crop, n leaching and soil content. pu did not affect (p>0.05) any of the variables; nf had a linear effect (p≤0.05) on the extraction of n (in n0 274± 15 kg n ha-1, 44.9 % less than n200) and leaching of n (98 ±19 kg n ha-1 in n100, 73 % less than n200). the levels of apparent effect of fertilization and fertilizer use efficiency were acceptable, but fertilization was not economically advisable. fertilization increased the amount of n leached, which is ecologically unfavorable. during the growing season of maize the amount of n in the soil was reduced, emphasizing the importance of legume pastures associated with grasses, to maintain high levels of productivity in this rotation.