Soybean Yield in Production Systems with Corn, Brachiaria and Nitrogen Fertilization.

The mean yield of soybean in Brazil did not increase significantly in the last few years. One of the reasons is the occurrence of periods of hydric deficit, which limits the efficiency of photosynthesis (stomatal closure), the nutrient transport to the roots and the mobilization of these minerals and photosynthates throughout the plant. Thus, strategies such as intercropping maize with forage for increase soil surface cover, in order to enhance hydric balance and reduce drought effects, has been adopted. Also, another factor influencing soybean yield is nitrogen (N) requirements and the ways to provide it. Studies performed in the country evidenced no yield increase in soybean when supplied with N fertilizers. However, little is known about its ability to take advantage of N applied to the system, mainly in precedent maize crop. The aim of this study was to evaluate yield of soybean when maize was previous grown single of intercropped with Urochloa ruziziensis and fertilized with N rates (0, 40, 80 and 120 kg ha^-1 N, as ammonium nitrate). The experiment was performed under field conditions in a distroferric Red Nitisol of Itambe, Parana, Brazil. We used randomized blocks design in a factorial scheme 2x4, with four replications. Both maize crop systems (single and intercropped) and N rates did not affect soybean yield (P>0.05), which attained 4492,0 kg ha^-1. Also, there was no interaction between them. One of the reasons was the absence of drought, which did not allow the manifestation of forage straw benefits in attenuating water loss. Yet, the great water availability may have helped the organic matter mineralization, releasing N, in addition to a good condition for the plants to establish symbiosis with fixing nitrogen bacteria. Thus, soybean could attend its demand without needing to use the remaining N from the fertilization of maize.