Estimating water retention and availability in cultivated soils of southern Brazil

Abstract

The objective of this study was to generate pedotransfer functions (PTFs) to estimate water retention and availability in conventionally-tilled soils and validate some PTFs available in the literature. Disturbed samples were collected from 34 subtropical soil profiles, corresponding to 85 horizons, to determine soil chemical and physical properties and PTFs were generated and validated. The correlations with physical and chemical soil properties were higher for soil water retention at specific tensions (r from 0.36 to 0.92) than for availability (r from 0.13 to 0.66). Water retained at 10, 33, 100 and 1500 kPa tensions may be accurately (i.e. R2 > 0.85) estimated by PTFs based on soil chemical and physical properties as predictive variables, but available water capacity may be estimated only with medium or lower accuracy (i.e. R2 < 0.85). Of those available in the literature, only PTFs of Giarola et al. (2002) at 10 kPa tension, of Masutti (1997) and of Oliveira et al. (2002) at 33 and 1500 kPa tensions for tropical soils, and of Reichert et al. (2009) at 10, 33 and 1500 kPa tensions for subtropical soils, estimated soil water retention with medium accuracy (i.e. R2 from 0.40 to 0.85). These PTFs had R2, root mean square error and mean error similar to PTFs that include only particle size distribution and soil organic matter. Further, as was the case for our study, these equations were all generated from a set of soils ranging from low (2:1 type clays) to high weathering (1:1 clays and oxides), thus demonstrating PTFs for hydraulic soil properties are region specific. Finally, none of the PTFs from temperate soils was accurate for estimating water retention in conventionally-tilled soils from subtropical environment, and thus should be replaced by the PTFs from this study.