Response of the castor bean (Ricinus communis L., cv. Al Guarany 2002) to different soil water tensions.

Com o incentivo ?? produ????o de biodiesel no Brasil, a cultura da mamona ganhou import??ncia no cen??rio agr??cola, visto que suas sementes tem alto teor de ??leo de boa qualidade. Aliada a estas caracter??sticas est?? a resist??ncia ?? seca, que envolve um aspecto controverso, pois o que se tem observado s??o baixas produtividades em condi????es de d??ficit h??drico. Em virtude disso, este trabalho teve como objetivo avaliar a resposta da cultura da mamona a diferentes tens??es de ??gua no solo, determinando o efeito das condi????es de d??ficit h??drico no crescimento e desenvolvimento da planta. Para tal, foi desenvolvido um experimento em ambiente protegido, com plantas de mamona da cultivar Al Guarany 2002. As plantas foram cultivadas em vasos nos quais foram instalados tensi??metros a 0,15 m de profundidade para monitoramento da tens??o de ??gua no solo. O delineamento experimental foi inteiramente casualizado, com tr??s tratamentos e quatro repeti????es: 1 tens??o mantida em 0,01 MPa; 2 quando a tens??ochegava a 0,03 MPa as plantas eram irrigadas para retorna-la a 0,01 MPa; 3 quando a tens??o chegava a 0,06 MPa as plantas eram irrigadas pararetorna-la a 0,01 MPa. No intervalo entre 30 e 105 dias ap??s a emerg??ncia (DAE) foram avaliadas quinzenalmente a transpira????o, a ??rea foliar, a altura da planta e o di??metro caulinar. Determinou-se ainda o tempo para in??cio da flora????o e altura de inser????o do primeiro racemo. Aos 105 DAE foram realizadas as avalia????es dos par??metros fisiol??gicos, potencial de ??gua na folha, firmeza da folha e resist??ncia estom??tica. Os resultados indicam que a mamona ?? sens??vel ao aumento da tens??o de ??gua no solo, sendo que em condi????es de maior tens??o ela diminui a transpira????o e o seu crescimento. O tempo para flora????o e a altura de inser????o do primeiro racemo foram maiores nas plantas submetidas a menores tens??es de ??gua. O potencial de ??gua na folha e a sua firmeza diminuiram com o aumento da tens??o de ??gua. O aumento da tens??o de ??gua no substrato aumentou a resist??ncia estom??tica nas folhas da mamoneira, principalmente com o aumento da demanda evaporativa da atmosfera.With the incentive of biodiesel production in Brazil, the castor bean crop has gained importance in the agricultural scenario, mainly because its seeds have high oil content of good quality. Being considered drought resistant plant in most reports of the literature, this is a controversial aspect because under water deficit conditions low yield has been recorded. Therefore this study had the objective to evaluate the growth and development of the castor bean submitted to different soil water tensions. A greenhouse experiment was carried out with plants of the cultivar Al Guarany 2002. Plants were cultivated in pots with one tensiometer installed at the 0.15 m depth to monitor the water soil tension. The experimental design was completely randomized with three treatments and four replications: 1- water tension maintained at 0.01 MPa; 2 when the soil water tension reached 0.03 MPa, water was added to until returning 0.01 MPa; 3 when the soil water tension reached 0.06 MPa, water was added to until returning to 0.01 MPa. Between 30 and 105 days after plant emergence (DAE) plant transpiration, leaf area, plant height and stem diameter were biweekly evaluated. The time lapse to onset of flowering and height of insertion of the first raceme were evaluated. Physiological parameters such as leaf water potential, leaf firmness and stomatal resistance were measured at 105 DAE. Results show that increasing soil water tension decreased the transpiration and growth rates of the castor bean plant. The time to flowering and height of insertion of the first raceme were greater for plants submitted to lower soil water tension. The leaf water potential and leaf firmness decreased as the soil water tension decreased. As soil water tension increased the stomatal resistance increased mainly with the rise of the atmosphere evaporative demand. Keywords: transpiration, water stress, growth e development