Efeitos da Adubação Nitrogenada sobre a produção da Mamona irrigada com Água e Efluentes de Esgoto doméstico tratado.

Abstract

The castor bean (Ricinus communis L.) can be considered as a commercial crop with multiple utilities, among them, the use of its seed oil for biodiesel production, a motor fuel considered ecologically clean. The present study was conducted under field conditions, in an Argissolo Acinzentado eutrophic soil, and had the objective to evaluate the castor bean yield (cultivar Nordestina BRS-149) response to nitrogen fertilization. The experimental design consisted of a split-plot model. One plot was irrigated with treated sewage effluent and the other with well water. Each plot was fertilized with five N rates in a form of Urea (T1=0, T2=30, T3=50, T4=70, T5=90 kgha-1 N), control treatment and three replications. The following parameters were evaluated: number of racemes/plant, first raceme length, 100 seed weight, kg of seed per hectare, first raceme height and stem diameter. The number of racemes/plant was significantly higher in the plot irrigated with treated sewage effluent than in the plot irrigated with well water. The type of irrigation did not cause differences in the first racemes lengths; however, differences occurred inside each plot as function of the N rate. The seed highest productivity was 2250 kgha-1 (rate of 90 kg Nha-1) for the plot irrigated with treated effluent, while was 2240 kgha-1 (rate of 50 kg Nha-1) for the plot irrigated with well water. The higher pH of the effluent may caused higher N volatilization, what may explain the higher N rate to reach maximum productivity in the effluent irrigated plot. The nitrogen fertilization caused significant increases in all parameters evaluated, except for 100 seed weight.