Avaliação da eficiência de uso da água no algodoeiro irrigado na chapada do Apodi segundo simulações do modelo SWAP.

Abstract

Cotton was in the twentieth century the main agricultural product of the Brazilian Semiarid. However, in the early eighties the cotton industry went into decline. This decline was mainly due to the cheapening of the product in the domestic market at subsidized prices as a result of the international market. The revival of cotton production is crucial for the development of the semiarid lands of Brazil However, this restoration depends on the adoption of new technologies in the production system, mainly related to water use, since the irrigation minimizes risk and maximizes the productive potential of cotton crop. Given this context, this research aims to evaluate the water use efficiency of irrigated cotton crop in semiarid lands of Brazil. The study was conducted by applying the SWAP model to simulate the effect of different irrigation treatments based on deficit irrigation (DI), in the evapotranspiration (ETc) and Yield (Y) crop. The irrigation efficiency was assessed by the Water Use Efficiency (WUEET) performance indicator based on evapotranspiration. The Soil, Water, Atmosphere and Plant (SWAP) model is a physically based, detailed agro-hydrological model that simulates vertical transport of water, solutes and heat in unsaturated/ saturated soils. The crop growth and development was simulated by the detailed module based on WOFOST. The model was calibrated with data from two experimental campaigns, in which the cotton ETc was determined by Bowen ratio technique. Measurements of soil water content, leaf area index and biomass were also collected in such campaigns. Seven water treatments were considered. The results showed that the water increase in irrigation water supply to increases in ETc. On the other hand, showed increases Y when subjected to treatments based on the DI to drop and if irrigation is abundant. Because of this behavior there was a significant quadratic relationship between Y and irrigation water supply. In turn, the WUEET had similar behavior to Y and also showed a significant relationship with the irrigation water supply. The treatment that showed the best performance was the T3-75%, whose irrigation accounts for 75% of the full irrigation. This treatment has WUEET equal to 0.54 kg m-3. The WUEET the seven experimental treatments ranged from 0.39 to 0.54 kg m-3.