Evaluating the Effect of Compaction on Soil Hydraulic Properties

Abstract

Soil compaction is commonly viewed by agronomists as an undesirable consequence of intensive agricultural activities arising from heavy machinery or livestock trampling. However, when induced at the bottom of furrows, it might help reduce the water loss during furrow irrigation. As such, understanding of how compaction alters soil hydraulic properties is essential for developing sustainable soil and water management practices. This study aimed to investigate the impact of compaction on soil hydraulic properties of a clay-textured Nitisol. Thirty undisturbed soil samples were collected from a depth of 15 cm in Koga irrigation scheme, Ethiopia, and subjected to five compaction levels: control (0%), 5%, 10%, 15%, and 20% volume reduction, each with six replicates. Saturated hydraulic conductivity was measured using the KSAT® apparatus with the falling head technique, while water retention and unsaturated hydraulic conductivity were measured using the HYPROP® system based on the modified evaporation method. Compaction reduced water retention and hydraulic conductivity, particularly in the wet range up to pF 3. Saturated hydraulic conductivity decreased by 9% to 78% from the lowest to highest compaction level tested. Compaction also increased bulk density (8% – 40%) and relative field capacity (4% – 10%) and decreased total porosity (6% – 33%), macroporosity (28% – 82%), air capacity (25% – 61%), and plant-available water content (8% – 17%). When compared with soil quality thresholds, compaction of 15% or more reduced plant-available water below optimal range (< 0.2 m3 m-3) and lowered saturated hydraulic conductivity below the threshold (8.64 cm day-1). While this study was designed to evaluate the efficiency of furrow irrigation subjected to compaction, the findings also emphasize the need for sustainable soil management to improve crop yield and soil resilience.Keywords: Hydraulic properties, HYPROP2®, KSAT®, Soil compaction, Soil physical quality