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

摘要

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 oatsassociated 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.