Adubação nitrogenada e fosfatada para a cultura da mamona.

Abstract

In Brazil, since the colonial period, the culture of castor bean had great economic and social importance, particularly for the Northeast region, due to the differentiated quality of its oil. Recently, with the establishment of the National Program of Production and Use of Biodiesel, its culture began to be stimulated in other regions of the Country, where the lack of research information still is great. The objective of this study was to evaluate the response of castor bean cultivars to the nitrogenous and phosphatic fertilizations in the conditions of the South region of Rio Grande do Sul. The study, comprising two experiments (nitrogenous fertilization and phosphatic fertilization), was carried out in the agricultural harvest of 2007/08, in a Planossolo Háplico (Albaqualf), in the municipality of Pelotas, RS. Two castor bean cultivars ('AL Guarany 2002' and 'Lyra') and five doses (0; 30; 60; 90 and 120 kg ha-1) of N or P2O5 were used, according to the experiment. The effects of the treatments on the nutrition and production of the castor bean were evaluated as well as the fertility of the soil after the harvest. In general, the nitrogenous and phosphatic fertilizations favored the nutritional state of the castor bean. The yield of the culture increased with the use of up to 84 kg ha-1 of N, being the dose of maximum economic efficiency 77 kg ha-1 of N. With regard to the response to phosphorus, the yield of grains increased with the use of up to 156 kg ha-1 of P2O5, for 'AL Guarany 2002', and of up to 90 kg ha-1 of P2O5, for 'Lyra'; the economic doses for these cultivars were, respectively, 134 ha-1 and 78 kg ha-1 of P2O5. The nitrogenous and phosphatic fertilizations promoted increase of the concentration of available phosphorus in the soil.