Effect of induced fire on soil water repellency in the Pine ( Pinus sabiniana) forest of Welihena, Matara

Abstract

Soil water repellency (SWR) is a reduction in the rate of wetting and retention of water in soil caused by the presence of hydrophobic coatings on soil particles. Most common methods to determine SWR are the water drop penetration time (WDPT) and molarity of ethanol droplet (MED) tests. Main aim of this study was to determine the effect of induced fire on SWR in pine forest, Welihena, Matara. Soil samples at different depth layers were collected for analysis. Induced fire experiments were carried out to determine the effect of fire intensities on SWR. According to soil textural analysis, soil was confirmed as loamy sand. Maximum WDPT (7.3s) was observed in the first layer of 0-2cm whereas minimum (1.48s) was in the deepest layer of 22-25cm. In fire experiment, time taken to complete the fire were 3.29minutes, 5.43minutes and 8.72minutes for 1st, 2nd and 3rd fire, respectively. Moisture content of soil layers of 0-2cm, 2-4cm and 4-6cm after fires varied between 23.2% and 18.1%. Moisture content decreases gradually from 0-2cm layer to 4-6cm layer when intensity of fire increases from 3.29minutes to 8.72minutes. The WDPT of surface soils were 43.86s, 162.5s and 415.2s after 1st, 2nd and 3rd fires, respectively. And the WDPT of the soil layers (0-2cm to 4-6cm) after 1st, 2nd and 3rd fires varied between 1.18s-5.89s, 1.14s- 7.57s, 1.2s-4.76s, respectively. Based on WDPT results, soil surface becomes severely water repellent from wettable/slightly water repellent when intensity of fire increases from 0 to 8.72minutes. In addition, SWR of soil layers of 0-2cm, 2-4cm, 4-6cm become slightly water repellent from wettable when intensity of fire increases from 0 to 8.72minutes.