Eficiência de uso da água e rentabilidade da cultura da mamona irrigada.

Abstract

This research had as its objective to determine the efficiency of water use and the profitabHity <5f irrigated castor bean culture. The experiments were conducted at the Experimenta! Station of lhe EMBRAPA iocalized in the municipality of Barbalha - in the state of Ceará, Brazil, during the years of 2005 and 2006. The cultivar used in the study was BRS Energia, of precocious cycle and low stature, with 120 days to harvest in an area of 1 ha for 2 years. The water consumption, in the different phenological phases during ali of the culture cycle, was performed by using the ratio energy balance method based on Bowen ( E t c - BERB). The coefficient of harvest (Kc) was obtained by the relation between (ETc - BERB) and reference evapotranspiration (Eto), estimated by FAO-Penmam- Monteith method. Total evapotranspiration of the culture during 2005 was 577.94mm, with a minimum consumption of 47.24mm (period of 12 days) in the initial phase and a maximum of 220.93mm (35 days) in phase IV. The cycle of the castor bean culture was 106 days. For 2006 the consumption was 552.28mm. The average productivity of the beans was verified at 3389 Kg.ha"1 for 2005 and 3221 Kg.ha"1 for 2006, with water usage efficiency at 0.498 and 0.474 Kg.m"3, for those respective years. The average values of Kc per phenological phase were 0.73; 0.92; 1.01; 1.11 and 0.87. In 2005 an experiment with the following depth was performed: 403.19; 512.74; 562.36; 627.59 and 679.94mm which resulted in a bean productivity of 2705.83; 2930.27; 3009.72 and 3178.88 and 3361.72 Kg.ha"1, respectively. In 2006 four water depths were studied: 541.1; 649.7; 801.8 and 934.8mm. The maximum productivity was 3245.8 Kg/ha"1 for 649.7mm, with a superior yield in 17% (2773,3 Kg), 29% (2518,4 Kg and 109% (1555 Kg.ha"1), in relation to the depths of 541.1; 801.8 and 934.8; respectively. In 2005, it was confirmed that the relation cost/benefit increased as the quantity of water applied was increased, reflecting in a greater economic response from the castor bean cultivar BRS Energia.