Comportamento de duas cultivares de mamona irrigadas sob fertilização do solo com NPK.

Abstract

The fertilization is a practice that normally increases the productivity of the cultures. Considering that the NPK needs of the castor bean are still unknown an study was conducted aiming to evaluate the effects of nitrogen, phosphorus and potassium on the growth and production of castor bean (Ricinus communis L.) cultivar BRS 188 Nordestina and BRS 149 Paraguaçu. For this, two experiments were installed in a greenhouse using a 2 x 2 x 2 factorial design completely randomized subjected to two leveis of nitrogen (Ni=200 and N2=300 kg ha"1), two leveis of phosphorus (Pi=150 and P2=250 kg ha"1) and two leveis of potassium (Ki=150 and K2=250 kg ha'1) with three replicates, totalizing 24 experimental units. The testimony corresponded to the treatment with the lowest leveis of NPK (N1P1K1). Soil water content was maintained at field capacity and monitored daily using a DIVTNER probe inserted into the soil throughout an access tube installed in each vase. Plant height, stem diameter, number and length of leaves were measured at 20, 40, 60, 80, 100,120, 140 and 160 days after planting. Castor bean production was evaluated measuring the length and weight of the raceme, the number of fruits, the amount of seeds by raceme, weight of 100 seeds, and oil and protein content of the seed. The combined application of the highest leveis of nitrogen, phosphorus and potassium was not enough for the plants to develop its productive potential. Nitrogen was the nutrient that promoted the highest growth, development and yield of the two cultivars. On fructification, both castor beans cultivars presented low content of nitrogen, phosphorus, potassium, calcium and sulfur and high contents of magnesium. Independently of the NPK leveis studied, the oil content of the seeds was under the ideal and admitted levei. Although the oil content of the seed was low, the nitrogen application increased the seed oil content. The application of nitrogen increased significantly the protein production.