Produção de espécies de Jatropha irrigadas com águas salinizadas.

Abstract

Jatropha curcas L.. Jatropha mollissima (Pohl) Baill and Jatropha gossypiifolia L. are oilseeds, belonging to the genus Euforbiaceae, that demonstrate a potential for biodiesel production and are used as raw material for the chemical industry. These species, however, fali short of scientifie data on crops irrigated with salinated waters. A field research was conducted at the agronomic and environmental research center of Paraíba State University (UEPB), Brazil, during the period of April 2009 through December 2010. The objective was to evaluate the salinity effects on plant growth, production, physiological indexes, phenological phases, and oil content as well as the impact on the soil. Treatments employed consisted of the combination of the three Jatropha species and five salinity leveis (1.20; 1.80; 2.40; 3.00 and 3.60 dS m' , at 25 °C), one drip irrigation depth to replenish reference evapotranspiration, plus three additional separate rainfed treatments to contrast with the saline treatments, totaling 18 treatments altogether. The experiment adopted a randomized complete block design divided in land plots (3x5 + 3), with three replications, totaling 18 plots and 54 subplots. Each plot was subdivided into three subplots, one for each Jatropha species, eachcontaining 18 plants and a total area of 67.5 m2 (9 x 7.5 m), and 15.0 m2 of useable plot area (4 plants). The following data were analyzed: growth, production, and physiological variables, seed oil content as well as the chemical attributes of the soil. The phenological phases of the three Jatropha species differed chronologically. Up to 165 days after transplanting, J. mollissima outgrew the other two species in plant height; J. curcas outgrew the others in stem diameter; J. gossypiifolia displayed the highest leave yield per plant and the highest leaf yield of the three Jatropha species occurred during the fructification phase. The highest plant height and stem diameter growth rates occurred during the vegetative growth, with distinguished results for J. mollissima in plant height rates and for J. curcas in stem diameter rates. The lowest plant height and stem diameter growth rates for the three species coincided with their productive phases. Electrical conductivity in the water content of up to 3.60 dS m 1 did not affect growth variables; production and oil content of the three Jatropha species. A rainfall volume of 1594.50 mm, up to 615 days after transplanting, contributed for a similar growth and yield of the Jatropha species both in the saline and rainfed conditions. Following 615 days after the transplanting, under the influence of salinity leveis, each plant yielded in average: clusters: J. gossypiifolia (951.18 clusters), /. curcas (280.95 clusters), J. mollissima (214.42 clusters); fruits: /. gossypiifolia (3,065.77 fruits), J. curcas (867.25 fruits), /. mollissima (480.05 fruits); fruit phytomass: /. curcas (2,148.93 g), J. mollissima (1,259.25 g), J. gossypiifolia (1,088.28 g); seed phytomass: J. curcas (1,477.82 g), J. gossypiifolia (334.72 g), /. mollissima (216.70 g) and oil content: /. curcas (27.81%), / gossypiifolia (22.36%), J. mollissima (19.58%). At 600 days after transplanting, the salinity leveis reduced the stomatical conductance, the transpiration and the net photosynthesis rate of the J. curcas. These variables, however, remained unaltered for J. mollissima and J. gossypiifolia. Soil washing through rainfall lixiviated the salts. At the end of the study, after 120 days under low rainfall, high evapotranspiration and irrigation with salinated waters, the hydrogen ion potential, the electrical conductivity of the saturation extract and the exchangeable sodium percentage of the soil increased, which rendered it slightly saline and sodic.