Soil amendment effects on field‐saturated and unsaturated hydraulic properties of sodic soils

Abstract Soil sodicity degrades soil structure and restricts water movement by promoting clay swelling, dispersion, and surface sealing, thereby reducing infiltration and hydraulic conductivity. This study aims to evaluate the effects of four soil amendments (elemental sulfur, gypsum, compost, and humate) on the hydraulic conductivity of sodic soils, both in the field and in the laboratory, across six farm sites in Utah and Wyoming. Field‐saturated hydraulic conductivity ( K fs ) was measured using a dual‐head infiltrometer, while lab‐saturated ( K s ) was measured using a falling head test, and unsaturated hydraulic conductivity was measured using the HYPROP 2 system during controlled drying. Across sites, field K fs values ranged widely from 1.5 to 38.9 cm h −1 , reflecting high spatial variability with measurements made 6–8 or 17–20 months after amendment application, depending on site establishment year. Laboratory measurements were conducted only for a subset of sites and treatments. At the sites evaluated, compost increased K s by 215% (3.04 vs. 0.96 cm h −1 ), while gypsum increased it by 70% (1.63 cm h −1 ). Lab measurements align with field measurements but vary in the magnitude of conductivity, potentially due to the presence of macropores in the field measurements and root biomass. Unsaturated hydraulic conductivity results revealed increased water permeability in gypsum and compost‐treated soil, with an increase in plant‐available water by 5%–7%, indicating enhanced soil permeability. Limited laboratory measurements showed higher hydraulic conductivity under gypsum and compost treatment than the control, but the results should be interpreted with caution due to restricted site and treatments in the lab, and field variability may have masked short‐term amendment effects.