Resposta da mamona à disponibilidade de água e matéria orgânica no solo, em dois ciclos com manejo de poda.

Abstract

The objective of the experiment was to study the sensibility of the castor bean cultivar BRS 188 to different levels of available soil water for plants and soil organic matter evaluating the effects on its growing, development and production. The experiment was conducted under field conditions at the Environmental and Agrarian Sciences Center, Campus 11, Universidade Estadual da Paraiba, Lagoa Seca, PB, located at a mean altitude of 634m, during the period of October 2008 to October 2009. The soil utilized was a low organic matter sandy clay loam. The experimental design used was a 2 x 4 factorial on a randomized-complete block design, constituted of two soil organic matter contents (5.0 and 25.0 g.kg'1) and four soil water contents (100, 90, 80 and 70% of the soil available water for the plants) with 3 replicates. On each 100 m2 parcel were cultivated 50 plants with a spacemen of 2m x 1m. The soil was fertilized with super phosphate in foundation with 120 kg ha"1 P205 and in coberture 100 kg ha"1 of K 2 0 and 100 kg ha"1 of nitrogen. The potassium and nitrogen fertilizer forms were potassium chloride and urea, respectively, fractionated in 10 days intervals and applied by fertiirrigation. The experiment was conducted during two cycles, the first of 180 days and a second one for another 180 days, after a drastic paring of the plant at about 30 cm from the soil surface. Soil water content was monitored every two days, using a Time Dominium Reflectometry technique (TOR). The results were submitted to analyses of variance (F test) and the means compared by the Tukey test. The quantitative factor, water levels, was studied by regression analyses. It was observed that organic matter and available soil water for plants increased the growing, the development and the production variables analyzed. The crop showed a high sensitivity to water deficit, decreasing severely its productive capacity with the decrease of the soil water content. The second cycle of the culture, presented a growth, development and production behavior similar to the one obtained on the first cycle, with very high quality characteristics of final product demonstrating the technical feasibility of the use of a second cycle, obtained after the paring.