Soil water repellency under Eucalyptus stands of different age and its relationship with soil hydrological function and soil organic matter

Abstract

Eucalyptus stands can modify soil hydrological functioning, by several mechanisms including the effect of thegrowing root system, changes in soil organic matter (SOM) and the occurrence of soil water repellency (SWR).This effect is expected to evolve with time, as tree root system develop and SOM is formed from tree litter. SWRcan prevent water from entering the soil, reducing infiltration, while the effect of roots and SOM can improvestructure, favoring infiltration. The aims of this study were: i- to determine the influence of Eucalyptus stands ofdifferent ages on soil physical and hydraulic properties and SWR phenomena; ii- to evaluate the effects of SOMcontent and composition on SWR; iii- to determine the relationship between SWR and soil physical properties; ivto compare different methodologies for SWR evaluation. The soil studied was a in a silty loam Typic Argiudollwith Eucalyptus stands of 3, 7, 11 and 32 years. Samples were taken to determine saturated and near saturationhydraulic conductivity, water retention curve, total organic carbon and different fractions of SOM, and SWR.Different parameters were used to estimate SWR, including the repellency index (RI), water repellency cessationtime (WRCT), modified repellency index (RIm), and a qualitative analysis of the shapes of cumulative infiltrationcurves. As main results, a reduction in total porosity (TP) in the first years of Eucalyptus plantation was found,followed by a steep increased in TP, mainly due to an increase in microporosity. Hydraulic conductivitydecreased with stand age, which was attributed to a decrease in macro and mesoporosity and porosity con­nectivity. SOM and most SOM fractions were not affected by stand age. RI was a consistent method to estimateSWR in Eucalyptus stands, while WRCT and RIm determination was more difficult when non classical shapes ofinfiltration curves were obtained.