Time Dependent Contact Angle of Soils Amended with Animal Manure and Fine Woody Debris

Abstract

Soil water repellency is a dynamic phenomenon, which is caused by low-energy surfaces where the attraction between solid and liquid phases is weak. Contact angle is one of the common ways to measure the wettability of a surface or material. The purpose of the present study was to determine the time dependence of the sessile drop contact angle of the soil amended animal manure and fine woody debris. The sessile drop contact angle was measured Cattle manure (CM), goat manure (GM), and poultry litter (PL) were used to represent animal manures. Casuarina (CE) dried leaves and saw dust of Mango (MN) and Domba (DOM) were used to represent fine woody debris. Contact angle was measure with sessile drop method. The contact angle was initially greater than 90° except in PL added samples. However, within 5 s, the contact angle of CM and GM added soils decreased to be below 90°, whereas that of PL, to reach 0°. In soils amended with 50% animal manure, contact angles of all the samples were initially greater than 120° The contact angle of all the samples decreased exponentially with time. Adsorption of water molecules to low-energy hydrophobic organic surfaces can increase the net surface free energy of the soil and weaken water repellency. Accordingly, the reduction of contact angle with time can be explained as a result of the adsorption of water molecules onto soil-water contact surface and the consequent increase in surface free energy.