Adjusting the water retention curve for retractable soils•

Abstract

The soil water retention curve (SWRC) relates moisture to soil water retention energy (matrix potential). The calculation of the volumetric humidity considers the sample volume. In retractable soils, this volume varies according to the drying or wetting of the soil, which can result in errors in the calculated moisture. The objective of this study is to quantify the volume variation in retractable soils and to elaborate the SWRC via the traditional method, which does not consider soil retraction, and a second method, called adjusted, that considers the phenomenon of soil retraction. Soil samples have been collected in horizons A and B from six soil profiles Thus, for retractable soils, it is recommended that the adjustment of the SWRC be carried out considering the actual volume of the soil (retracted), which varies for each matrix potential applied. This adjustment reduces errors, mainly in determining the permanent wilt point and available water.