Efeito do conteúdo de água do solo, monitorado com TDR, sobre o desenvolvimento e produção de duas cultivares de mamona.

Abstract

Although the castor bean plant has the production reduced by water deficits, due to the capacity to resist low precipitation conditions it is a good alternative for income generation. The castor bean has a great economical importance, they are utilized the leaves, the stem cellulose, the oil and the tort extracted from the seeds, standing out the oil due to its high content of graxo ricinoleico acid and because substitutes the petroleum derivates. The lack of information on the effects of water deficit in areas where low precipitation do not satisfy the plant evapotranspiration needs , justify the present work which study the effect of the water deficit, monitored by a Time Dominium Refractometry (TDR) method on two castor bean cultivars ( BRS-149 and BRS-188). The experiment was conducted on a green house located on the Campus 1 of the Federal University of Campina Grande, Paraiba State, Brazil, during the period of February 23 to August 5 of 2004. The experimental design was a 2 x 4 factorial, with the castor bean cultivars and the soil water content (40, 50, 80 and 100% of the available water for the plants) as treatments. It was analyzed the TDR performance to monitor the soil water content, the germination, germination speed index, plant height, height growing rate, stem diameter, number of leaves, foliar area, days for the emission of the first inflorescence, number of inflorescences, phytomass, root/aerial part rate, water use and efficiency, macro and micronutrients content of the leaves, stem and roots, and oil and protein production of the seeds. Analyses of the results show that the TDR method was very efficient to determine the soil water content and to program the irrigations. With respect to the castor bean resistance to water deficit, the statistical analysis showed no significant differences among cultivars, neither the register of physiological adaptations to this condition, being very sensitive to water deficit, reducing drastically the capacity to convert the consumed water in dry matter as the soil water decrease. However, under the absence of water stress, both cultivars are very efficient to do this transformation, leading consequently to a greater fruit production per productive unit.