NITROGEN BALANCE IN FORAGE MAIZE WITH DIFFERENT FERTILIZATION AND PHASE OF CROP ROTATION WITH PASTURES

The aim of this study was 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 (N-0), 100 (N-100) and 200 (N-200) 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 N-0 274 +/- 15 kg N ha(-1), 44.9% less than N-200) and leaching of N (98 +/- 19 kg N ha(-1) in N-100, 73 % less than N-200). 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.