Crescimento, estado nutricional, acúmulo de nutrientes e produtividade da mamoneira em função da variedade e da adubação fosfatada

Abstract

The obtaining and selection of new varieties of castor bean, associated with the cultural practices of fertilization and of pest and diseases control, have been the technologies identified as the most promising to increase the productivity of these oilseed in several Brazilian regions. There are only a few studies conducted on castor bean in Brazil, in relation to fertilizer, the search on phosphorus should be prioritized, therefore, the Brazilian soils in general, are deficient in this element. Moreover, this nutrient participates of the energy production through the plant and influences in the absorption and metabolism of several elements too.Thus, the objective to assess the effect of phosphorus on growth sexual expression, nutritional status, accumulation of nutrients and the productivity of two castor bean varieties. The research was conducted in the experimental area of the Agricultural Center of Sciences, located in the city of Rio Largo, Alagoas. The study was a 5 x 2 factor, consisted of five doses of P (0, 20, 40, 60 and 80 kg ha-1) and two castor bean varieties, BRS 149 Nordestina and BRS 188 Paraguaçu, with the treatments distributed in randomized blocks, with four repetitions. The soil of the experimental area was examined and received limestone in sufficient quantity to raise the saturation by bases to 60%. Varieties of castor bean seedlings were produced in a greenhouse, which were only transplanted into the field when they showed about 25 cm of height. Holes of 30 x 30 x 30 cm were made, separated by 1.0 x 3.0 m, and at the bottom of them triple super-phosphate was applied in quantities equivalent to doses established for each treatment. At the 30, 60, 90 and 120 days after transplanting (D.A.T) to determined the leaf area and the heights of the plants. On the 50th day, D.A.T. collected the +4 leaves for evaluation of the nutritional status of the plants and on the day before, covering fertilization was done, using the ammonium sulfate and the potassium chloride in doses equivalent to 30 and 60 kg ha-1 of N and K, respectively. The development of the reproductive organs was also evaluated through the length of the primary custer and the following, the numbers of custer produced during the entire cycle, productivity of seeds and the accumulation of biomass and nutrients in the upper parts. For the leaf area, the fertilization effect was only noticed at the 30 and 120 days; and for the height of the plants, some effect was only noticed at the 30 DAT, both being squared. The phosphate fertilizer only influenced in the leaf content of iron, however, there was a linear effect for the accumulation of N and quadratic for the accumulation of P and K. There was an varietal effect in leaf levels, which in the BRS 149 Nordestina variety were found the largest levels of N and least of Ca, without having a significant difference for the other nutrients. The quadratic effect of phosphate fertilizer was verified for the size of the primary custer, the number of custer produced, productivity of seeds and accumulation of dry matter. The varieties showed difference in the number and in the length of the primary custer and following, the largest quantity being verified in the plants of the BRS 188 Paraguaçu variety and longest lengths in the BRS 149 Nordestina variety.