Effects of Heating on Organic Matter Induced Soil Water Repellency

Abstract

Soil organic matter plays an important role in making a soil wettable or repellent. Water repellency produced by heating of non-repellent organic matter in soil is common on burned forests and watersheds. The objective of the present study was to identify the effect of laboratory heating on wettability of organic material amended soils. Goat manure (GM), poultry litter (PL), Casuarina (CE) leaves, and three types of fine woody debris namely Alstonia (AL), Domba (DO), and Mango (MN) were used to represent organic materials which were heated to temperature levels of 27 ‘C, 60 C, 100 C, 200 C for a 6 h heating duration. The water drop penetration time (WDPT) was used for the assessment of wettability. Samples with 50% GM showed the lowest WDPT of ~ 60 s, whereas those without organic material amendment showed the highest WDPT of 0 s within temperatures of 27 °C to 100 °C. Wettability of samples with animal manure did not show a considerable alteration with increasing temperature up to 100°C. Among the plant materials, 50% CE and DO showed W DPT>3600s. The WDPT of samples with 50% AL (57 s to 963 s), 50% MN (9s to 8 8 s), and 5% CE (32s to 133s) increased with increasing temperature from 27 °C to 100°C. Wettability of most plant materials decreased when the temperature increased. All the animal manure and plant material amended soils, except those with 50% PL, became completely wettable (WDPT = 0 s) when the samples were exposed to 200°C. This might be explained as a result of the removal of organic matter as C02 and H20 under high temperature heating. Reason for PL added soils to show a measurable WDPT after heating to 200 °C might be the incomplete removal of organic matter as a temperature higher than 200 °C is required for the loss of organic matter on ignition.