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.
