Water Repellent Effects off Organic Amendments on Saturated Hydraulic Conductivity of Surface Ultisols

Abstract

Organic amendments have the potential to generate soil water repellency. Since water repellency limits surface water entry, it might impose severe impacts on soil hydrology. Extensive organic manure usage is practiced in Sri Lanka to maintain soil fertility without considering subsequent water repellency effects on soil hydraulic properties. Slightly induced water repellency is found to increase soil aggregate stability. The objectives of the present study were to explore the manure induced water repellency effects on saturated hydraulic conductivity (1W) and to find out any detrimental effects of extra 2% hydrophobic organic manure addition on the Ksot. A surface Ultisol soil was mixed with powders of cattle and goat manure, Gliricidia sepium and Casuarina equisetifolia leaves in 5%. Other samples were prepared by mixing 2% Casuarina and 5% of manure separately to induce slight hydrophobicity. The persistence and the degree of water repellency were tested using water drop penetration time test and sessile drop contact angle method. The Ksat was measured using the falling head permeameter. The measurements were taken at 1, 3, 7, 14 and, 30 day. The data were analyzed with ANOVA using SAS 9.1 statistical software. Under extra 2% Casuarina addition, water repellency increased slightly. The samples with only 5% manure showed higher Ksar (17-42 cm/h) on the 30th day. However, soil with extra 2% Casuarina, the values didn't extremely increase and, they were in the favorable range (10-20 cm/h) for the crop growth. The Ksat varied negatively with the increasing water repellency without significant differences at 0.05 probability level between those with and without 2% Casuarina, revealing that the slightly induced water repellency would not be detrimental on saturated hydraulic conductivity.