Produção de pinhão manso irrigado com água residuária, em função de reposição da evapotranspiração.

Abstract

The physic nut (Jatropha curcas L.) is an oil producer plant; it belongs to Euphorbiaceae's family, which is a native species from American continent, and that is being considered as an alternative for biodiesel's production. This research had as objective to study the possible effects of irrigation with wastewater from domestic sewage, under different levels of evapotranspiration replacement, on the growth and development of physic nut, as well as the effects of irrigation on soil chemical properties. The experiment was carried out in drainage lysimeters under a protected area belonging to Universidade Federal de Campina Grande, Technology and Natural Resources' Center of Academic Unit of Agricultural Engineering. The experimental design had randomized blocks with four replications and it had studied five levels of water's replacement - Nr (Nri = 0.25, Nr2 = 0.50, Nr3 = 0.75, = Nr4 = 1.00 and Nrs = 1.25 of evapotranspiration - ETc), and a control treatment (T), in which the plants were irrigated by potable water, and received 100% of ETc. The experimental unit was constituted by two grown plants in separate lysimeters. The irrigations were performed according to a frequency of two days; the water's volume applied in each treatment was determined by water balance, based on the treatment Nr4 . The irrigation with wastewater allowed a best growth and development of plants, especially at treatments without water stress. The variables of growth (plants' height, stem diameter, number of leaves and leaf area) were affected by levels of evapotranspiration in all studied periods, but were more intensely affected in leaf area. Plants that were irrigated under the treatment of 1.25 of ETc presented the highest growth rates. The maximum quantum efficiency of photosystem I I was influenced by the levels of water's replacement of ETc only after 140 DAT (days after transplanting). The average production of irrigated plants with wastewater exceeded the control treatment. There was an increase of 648.80% in relation to average number of fruit clusters, 1515.61% in relation to average weight of seeds, 1423.20% in relation to average weight of fruits and 976.39% in relation to average number of fruits, between treatments Nri and Nr5 . The oil's content in seeds varied with period and treatment, it was reaching the maximum value of 42%. The variables of water balance, water's total consumption, crop's total evapotranspiration and medium evapotranspiration, increased with increasing levels of soil's moisture. The irrigation with sewage's effluent increased soil fertility, which resulted in higher concentrations of N and P in the layer of 0-10 cm, and K, Ca, Mg and Na in the layer of 10-20 cm deep. The concentration of soil's salts varied with depth, it became more saline in the deeper layers, including higher values of electrical conductivity of saturation's extract. In the soil surface depth it was verified an increase in pH.