Maize Yield As Affected By Topdressing Nitrogen and Intercropping Systems.

Nitrogen (N) fertilization is essential for maintaining high yield in tropical maize. However, determining the better way to fertilize remains a challenge in systems with intercropped forages. It is important to consider the changes in the nutritional requirement that these integrated systems promote. Moreover, in a short term the vigorous root system of these grasses can not only modify the soil physical properties, but also increase the release and cycling of nutrients. The aim of this study was to evaluate maize grain yield with N in topdressing for maize production systems intercropped or not with Urochloa gender grasses. The plots were carried out under field conditions in the fall/winter season of 2015, in a Red Nitisol of Itambe, Parana, Brazil. The experimental design was a 2x3 split-plot in randomized blocks with four replications. The N fertilization conditions were: 50 kg ha^-1 of N (as ammonium nitrate) at the time of sowing, for all treatments, and the presence or absence of 100 kg ha^-1 of N in topdressing. The production systems were: single maize (Zea mays) and maize intercropped with Urochloa ruziziensis or Urochloa brizantha. Yield was calculated based on the grain mass measured at the plots (g m^-2), converting to kg ha^-1. There was interaction between the factors. The yield was influenced by topdressing fertilization (P<0,01), wherein the applied amount secured an average increase of 1775.6 kg ha^-1. The nutritional intake of topdressing linked with the high requirement and important role that the N plays in metabolic sphere ensured the yield increase. Without topdressing, the cycling effect promoted by U. brizantha roots increased maize yield in relation to the single system. This forage presents more upright growth habit, lower roots and good development under shade. Thus, some intercropping systems can be more productive in regions with N fertilization restrictions.