Índices de área foliar e SPAD da soja em função de culturas de entressafra e nitrogênio e sua relação com a produtividade

Abstract

The objective of this work was to evaluate the effect of winter crops and nitrogen fertilization on the evolution of leaf area indices and SPAD of soybean, as well as the relationship between these variables and grain yield of soybean. The experiment was carried out in a randomized block design with split-plot scheme and five replications during 2016/17 and 2017/18 cropping seasons. The winter crops were allocated to the plots: palisadegrass (Urochloa ruziziensis), crotalaria (Crotalaria spectabilis), maize (Zea mays) with 0 and 80 kg N ha-1 topdressing, wheat (Triticum aestivum) and fallow. Two levels of N for soybean were applied at sowing time (0 and 30 kg N ha-1). The winter crops influenced LAI and SPAD index in the vegetative growth and flowering phases of soybean, but during grain filling these effects were not present. The application of mineral N at sowing soybean increased the LAI and SPAD index only in the vegetative and flowering stages, without affecting grain yield. In the first cropping season, at the beginning of flowering, LAI and the SPAD index were negatively correlated with grain yield, but in the second cropping season these correlations were not present.