DESENVOLVIMENTO DE MODELO MATEMÁTICO PARA PREDIÇÃO DA APLICAÇÃO DE NITROGÊNIO EM COBERTURA NA CULTURA DO MILHO EM ÁREA DE INTEGRAÇÃO LAVOURA-PECUÁRIA

Abstract

Maize (Zea mays L.) is a crop widely used in Brazil and in the Southern region is cultivated under several production systems including crop-livestock integration (ILP). The fundament of these systems is the cultivation of forage crops during winter and grain crops during summer in the same area. Among all the challenges in these systems, there is a need to define the optimal dose of nitrogen (N) to obtain the maximum technical efficiency (MTE) and maximum economic efficiency (MEE). Therefore, the objective of the study was to develop a mathematical model to obtain the MTE and MEE as a function of N doses applied in the winter pasture and in the maize crop during summer season, as well as to evaluate the effect of grazing on maize yield under a crop-livestock integration system. The study was conducted in Guarapuava, PR, Brazil during five growing seasons: 2007/2008, 2009/2010, 2011/2012, 2013/2014, and 2015/2016. The experiment was carried out in a randomized complete block design with sub-sub-plots in three replications. The main plot consisted of the N doses (0, 75, 150, 225 kg ha-1) applied in the winter pasture (Lollium multiflorum and Avena sativa), the subplot was comprised of grazing by sheep (presence or absence), and the sub-sub-plot contained the N doses (0, 75, 150, 225, 300 kg ha-1) on the maize crop during the summer season. A mathematical model was developed to obtain the MTE and MEE, as well as to calculate the efficiency of the maize in converting the N applied into grain yield. The N doses that represented the MTE and MEE had little or none alteration among growing seasons or hybrid used. It was verified that the difference in yield was due to the efficiency of the plant in converting the N applied into grain yield. It was also observed that when N is not applied on the winter pasture the MTE dose is 267 kg ha-1, whereas when N is applied on the winter pasture the MTE is reduced, which indicates a residual effect from the N applied during the winter season. The results suggested that the maize crop, in succession to Poaceae, had a defined MTE dose, which was independent of growing season and hybrid adopted.