Use of microlysimeters to determine soil water evaporation as a function of drainage

The aim of this study was to test two models and two sizes of microlysimeters to determine soil water evaporation as a function of the removal of water by drainage at the bottom of the units. The experiment was conducted at the experimental field of the State University of Mato Grosso (UNEMAT) in Tangará da Serra, Mato Grosso, Brazil. Soil water evaporation was determined using microlysimeters constructed from rigid PVC tubes, of which two models and two sizes were tested. The four microlysimeter treatments were: 100 mm diameter without drainage (ML100WD), 100 mm diameter with drainage (ML100D), 150 mm diameter without drainage (ML150WD), and 150 mm diameter with drainage (ML150D). The microlysimeters were fitted to an irrigation blade of 60 mm and compared to applications with four irrigation blade sizes (15, 30, 45, and 60 mm). Water evaporation from the soil was obtained from the mass variation of the microlysimeters, and was then compared to the soil water evaporation determined using weighing lysimeters. The obtained data were analyzed using descriptive statistical techniques, tests of means, and regression analysis. The soil water evaporation values present significant differences between the two microlysimeter sizes (100 and 150 mm diameter) and the two models (with and without water drainage). Soil water evaporation is affected by the water drainage that occurs at the bottom of the microlysimeters. There was no difference in soil water evaporation between irrigation rates within the same microlysimeter size and model. The two models and the two microlysimeter sizes tested can be used for the quantification of soil water evaporation, due to the high determination coefficients observed when compared to the evaporation observed with the weighing lysimeters.