Teor de clorofila, exportação de nutrientes e desempenho agronômico de híbridos de sorgo granífero em diferentes épocas de semeadura

Abstract

Sorghum is an extremely important crop for the second season, particularly in Brazilian savannah. Information about the development of the crop in different sowing dates, prompt and accurate fertilizer management and use of adapted cultivars are important for making decision by farmers. Thus, studies were conducted to evaluate the productive performance and concentration of nutrients in grain sorghum hybrids in different sowing times and stages of development, to determine chlorophyll contents in the leaves of sorghum hybrids at growth stages in different sowing dates, and to generate data on agronomic characteristics and the exportation of macronutrients by grain in different sowing dates. Experiments were done in contiguous areas in four sowing dates. The first one was sown on February 26 2013 and the others 17, 30 and 41 days after the first sowing - (DAFS). The experiments were conducted in a randomized complete block design with 9 grain sorghum hybrids and four replications. Each sowing date was considered an individual experiment, and grouped analysis was done to compare characteristics. Macronutrient contents and SPAD index data were evaluated in three different stages within the plant cycle, characterizing the experiment in a grouped analysis of split plot (development stage - subplots), with factorial in plot (hybrid x sowing time). Pearson s correlation coefficients for the variables macronutrient and SPAD index were calculated. Macronutrient content (g kg-1) exported grain by four of the nine hybrids planted in the four periods, in Votuporanga, was evaluated. Sorghum hybrids productivity varied according to the sowing dates. Macronutrient contents varied in different development stages and sowing dates. SPAD chlorophyll index values had positive linear correlations with nitrogen levels in the phenological stages evaluated. The mass of one thousand grains of sorghum hybrids varied depending on the sowing dates. Exportation of macronutrients by sorghum grains followed the decreasing order: N> K> P> Ca> Mg> S. The mean values of macronutrients accumulation to produce one ton of grain sorghum grains are 20.5 kg N, 3:33 kg P, 3.70 kg K, 3:49 kg Ca, 1.77 kg Mg, and 0.72 kg S.