Características de chuvas produzidas por pivô central e seus efeitos sobre o solo

Abstract

The characterization of the artificial rain produced by a center pivot and its effects over the soil was carried out at the Hydraulics Laboratory of the Universidade Federal de Lavras with a center pivot simulator module. Super spray emitters with 6.94; 8.33; 9.33 and 10.12 mm nozzles and concave pads presetting 36 medium groves were used. The irrigation simulator mainline containing five outlets, in a 2.8m spacing, was mounted at a 4,5m height and drop pipes were used in order to adjust emitter height to a 2.70m value. Center pivot displacement was simulated by means of a self propelled device with a 0 to 350 m h¹.range of controlled speed. Experimental units were soil columns build with 250mm PVC pipes. Columns were filed with 2,0mm sieved air drayed samples of a Latossolo Vermelho Amarelo Soil presenting a sandy clay loam texture. Center pivot precipitation was characterized in terms of precipitation rate, drop size distribution and kinetic energy. A complete randomized experimental design with 3 replication of 12 treatments, representing kinetic energy varying from 175 up to 875 J m-², was used. Evaluated soil properties were: soil-water retention, runoff, saturated hydraulic conductivity, and splash. The F Test was used in order to identify differences among treatments and linear regression was applied to values showing significant differences. In order to verify F test presuppositions, both tests Shapiro-Wilk, for error normality, and Barllet, for variance homogeneity, were held. The results showed that the 2.28m spacing among emitters produced high water application uniformity, and the effect of the application of the rain produced by the center pivot precipitation over the runoff and splash reached its maximum with kinetic values varying from 350 to 500 J m-2 mm-1 keeping the same values for kinetic values from 613 to 875 J m-2 mm-1. The verified hydraulic conductivity reduction of saturated soil can be attributed mainly to the first cycles of soil surface wetting and drying. The retention of water at 10 kPa tension in the 5mm soil layer did not suffered any alteration due to the irrigation process.