Philippine Journal of Science
150 (6A): 1407-1415, December 2021
ISSN 0031 – 7683
Date Received: 19 May 2021

Unsaturated Soil Hydraulic Conductivity (Kₕ)
and Soil Resistance under Different Land Uses of a Small
Upstream Watershed in Mt. Banahaw de Lucban, Philippines

Ronald C. Garcia^1,2* and Marco A. Galang³

¹Graduate School, University of the Philippines Los Baños, Laguna 4031 Philippines
²Department of Forestry and Environmental Science, College of Agriculture
Southern Luzon State University, Lucban, Quezon 4328 Philippines
³Institute of Renewable Natural Resources, College of Forestry and Natural Resources
University of the Philippines Los Baños, Laguna 4031 Philippines

*Corresponding author: rcgarcia@slsu.edu.ph

 

ABSTRACT

 

Soil hydraulic conductivity influences hydrologic processes and the ability of watersheds to provide ecosystem services. Like most soil properties, however, it is highly spatially variable at different scales due to biophysical and anthropogenic factors. To quantify spatial variability, the study assessed the influence of land use/land cover (LULC) on soil hydraulic conductivity and compaction, as reflected by soil resistance in a small upstream watershed. Compaction was measured using a soil compaction tester and the unsaturated soil hydraulic conductivity (Kh) was estimated in the field using the inverse auger hole method. Measurements were made across six LULC: agriculture (Agri), coconut with agricultural crops (Coco + Agri), coconut with pasture (Coco + Grass), coconut with forest (Coco + Forest), reforestation area (Refo), and forest (Forest). Measurements were taken at 0–30 cm and 0–50 cm soil depths. Results showed that soil hydraulic conductivity and resistance significantly differed across LULC and soil depths. Soil resistance averages 0.83 MPa for all LULC at 0–30 cm depth, which was significantly lower (p = 1.184e–04) than 0–50 cm depth. Coco + forest recorded the highest soil resistance (1.01 MPa at 0–30 cm and 1.82 MPa at 0–50 cm), while Coco + Agri has the lowest resistance. Pairwise comparison of means also revealed that Forest at 0–30 cm depth had significantly higher (p < 0.01) Kh at 1.18 cm min–1 compared with other LULC across depths. Kh at 0–30 cm depth averages 0.57 cm min–1 for all LULC, which is significantly higher (p = 3.229e–02) than 0–50 cm depth. This indicated a decreasing hydraulic conductivity with increasing soil depth. This implies that strategies for promoting groundwater recharge and sustaining freshwater supply for lowland communities, in general, should be founded on LULC decisions, especially in upstream watersheds.