Yield-components of the castor-bean as a function of nitrogen fertilization and defoliation levels

Abstract

The objective of this study was to evaluate the growth and yield components of castor beans subjected to nitrogen fertilization combined with the artificial defoliation of the plant. The experiment was carried out at the Experimental Station of the Paraiba State Agricultural Company (Emepa-PB) located in the town of Alagoinha-PB, between the months of April and October, 2009. Five levels of N-fertilizer (00, 30, 60, 90, 120 kg ha-1) were used, combined with four levels of artificial defoliation (00, 20, 40, 60%), distributed in a randomized-block design, in a 4 x 5 factorial arrangement, with four replications. Plant height, stem diameter, number of nodes, 100-grain mass and grain yield were evaluated. Growth variables increase with the levels of N-fertilizer at defoliation levels of up to 20%. From this level on, there is a tendency for greater vegetative growth with the application of lower doses of nitrogen. Both the 100-grain mass and grain yield increase at N-fertilizer doses of less than 120 kg ha-1 and defoliation levels of up to 40%, showing that there is a positive correlation between these yield variables of the castor bean. Artificial defoliation, when combined with nitrogen fertilisation, causes changes in the growth and yield components of the castor bean, it being important to assess to what extent the application of N-fertilizer is economically viable, and the possibility of using alternative sources of this nutrient.