Efeito da variação espacial e temporal do tempo de aplicação no desempenho do sistema de irrigação dos sulcos.

Abstract

The main purpose of this research was to verify the effects of the temporal and spatial variations in the water application time at the end of the field on the performance of a furrow irrigation system from the Sao Goncalo irrigation district, operated under cutback flow conditions. For quantifying the spatial and temporal variations in the water application time, as a consequence of others variations in the field and operational parameters, evaluations were performed in six furrows, chosen in a such way to mostly embrace variations in the cross sectional side of the area, for each irrigation event along the crop season. In these evaluations, the water depth required, the furrow inflow and outflow, the advance phase, and the furrow cross sectional area were measured. The infiltration opportunity time at the end of the field was estimated by the Kostiakov- Lewis equation, which was derived, in real-time, from the fitting of the simulated advance to the measured one, using the SIRTOM model. Also, the water application time was determined in a real-time basis, given by the sum of the advance and opportunity times at the end of the field. The SIRMOD model was used to forecast the performance of the irrigation system, which was operated in a way to establish the adequate irrigation condition. The results show a substantial effect of the water application time variations on the performance of the furrow irrigation system. Along the time and space, the minimum and maximum values of the application efficiency, of the runoff ratio and of the deep percolation ratio were, respectively, 33.1 and 95.3%, 0 and 61.3%, and 0.1 and 66.4%. These amplitudes generated maximum spatial variations along the crop season equal to 33.0, 162.0 and 140.5%, respectively, in the application efficiency, in the runoff ratio and in the deep percolation ratio. Spatially, the temporal variations were 26.3, 78.4 and 233.3%. This study shows the importance of performing a spatial and temporal systematic monitoring in the field parameter variations, so that to have an estimation of the irrigation system performance the most representative as possible of the global field conditions.