Soil Water Repellency Characteristic Curves for Selected Agricultural
Soils with Different Ranges in Total Organic Carbon in Murang'a, Kenya.
Abstract
Soil water repellency (SWR) is a temporary property of the soil that
changes the functionality of the soil across a soil-specific range in
soil moisture content (W). The severity and persistence of soil water
repellency in agricultural soils is important in understanding and
predicting its effects on the soil hydrological processes to optimize
plant growth. Therefore, this study aimed at characterizing the
persistence of SWR using Water Drop Penetration Time (WDPT) test;
evaluating the SWR curve as a function of gravimetric water content from
the WDPT results and finally developing relationships between SWR
parameters (SWRAREA and Wc) and soil properties (TOC, Sand, Silt, Clay)
to understand the persistence of SWR and its effect on water flow. The
degree of SWR as a function of soil moisture content was measured and
monitored from oven-dry conditions to the water content at which the
soils turned hydrophilic (Wc). The total SWR (SWRAREA) was calculated as
the trapezoidal area under the SWR-w curve. A total of 37% of the soils
investigated were water repellent. The soils investigated had a wide
range in clay (10-40%) and TOC (0.67-6.08%). The SWR-w curves were
either single or double peaked. SWRAREA ranged from 8.38 second/%soil
moisture content to 24.91 seconds/%soil moisture content. TOC was the
most important soil property in explaining the total degree of
SWR(SWRAREA) and Wc. Inclusion of Clay and silt in the Multiple Linear
Regression (MLR) expression of SWRAREA significantly improved the
prediction of SWRAREA to 85%. Further, an upper limit critical water
content was derived from the simple relationship between the Wc and TOC,
which could be applied to improve irrigation practices of agricultural
soils of Murang’a County in Kenya. It is however advisable to develop
soil type specific models for Wc as a function of TOC when more
comprehensive data is available for each soil type.