Retenção e disponibilidade de água em diferentes solos do Rio Grande do Sul

Abstract

Soil is a great water store for plants, and controls important stages of the hydrological cycle. The soil’s ability to retain and store water depends on the texture, structure and depth of the soil, The objective of this experiment was to determine the water retention curve (CRA) for different RS soils with different textural classes, calculate the amount of total water stored and ranges of water available for the surface horizon, determine the field capacity, as well as carry out the comparison of real results of the methodologies adopted by ZARC. The experiment was developed in laboratory 102 of pedology and soil physics at UFFS campus Cerro largo- RS. Samples of the A horizon of 12 soils from RS were used. The soils were air-dried, macerated and sieved through a 2 mm mesh. Particle size analysis was carried out with these samples using the pipette method. To carry out the CRA soil samples were placed in rings of 100 cm³ in volume and saturated with water. 4 repetitions were made for each soil. After saturation, the samples were subjected to stresses of 6 and -33, -100, -500, - 100 and -1500 kPa in the Richards chamber. Using CRA data, soil water availability ranges soil density and porosity, and soil density and porosity were calculated. Pearson correlation analyzes were also carried out between water retention and other physical properties of the soil. The data obtained were subjected to analysis of variance and the means compared using the Scott Knott test at 5 % significance. The measured water retention date was also compared with the data estimated by the methodology currently used by ZARC. Only two mapping units obtained the same results as AD measured in the laboratory and AD estimated as predicted by Zarc, in the other mapping units a significant difference was obtained. Agricultural zoning does not take into account soil density total porosity, macro and microporosity, and these influence wter retention in the soil. The Zarc AD method needs to be improved, as AD in the soil is not a consequence only of the granulometric composition.