Effect of exudates of Chaitophorus leucomelas on soil hydraulic properties

Abstract

Soils may develop hydrophobic properties, causing either resistance to water infiltration or slowing the process. The aim of this study was to evaluate the effect of exudates of Chaitophorus leucomelas Koch, an aphid parasitic to Populus sp., on soil hydraulic properties and water repellency. Ch. leucomelas infested and non-infested sites were evaluated, using four randomly distributed replications for each case. The unsaturated hydraulic conductivity (K_ns) was measured using a tension disc infiltrometer at supply pressures of -10, -20, -40 and -60 mm, estimating saturated K (K₀). Hydrophobicity was determined in laboratory using the Rindex, based on water and ethanol sorptivity. Both sites showed a hydrophobic behavior when the soil was air dried, being higher in the Ch. leucomelas infested site, however, the hydrophobicity was lost upon wetting the soil. The infiltration of water decreased with the presence of the parasite, but the spatial variability prevented the occurrence of statistically significant differences between sites. The hydrophobicity and the K_s evaluated at -10 mm were exponentially fitted, which ensures that the behavior of K_ns depends not only on the pore size distribution of the soil, but also on the proportion and distribution of the soil organic matter. Finally, K_ns is presented as a tool to assess soil hydrophobicity at low pore water pressures to assess erosion in forest plantations.