Effect of Long-Term Semiarid Pasture Management on Soil Hydraulic and Thermal Properties

Semiarid pasture management strategies can affect soil hydraulic and thermal properties that determine water fluxes and storage, and heat flow in unsaturated soils. We evaluated long-term (>10 years) perennial and annual semiarid pasture system effects on saturated hydraulic conductivity (k), soil water retention curves (SWRCs), soil water thresholds (i.e., volumetric water content (θ_v) at saturation, field capacity (FC), and permanent wilting point (PWP); plant available water (PAW)), thermal conductivity (λ), and diffusivity (D) within the 0-20 cm soil depth. Forage systems included: Old World bluestem (Bothriochloa bladhii) + legumes (predominantly alfalfa (Medicago sativa)) (OWB-legume), native grass-mix (native), alfalfa + tall wheatgrass (Thinopyrum ponticum) (alfalfa-TW), and annual grass-mix (annual) pastures on a clay loam soil; and native, teff (Eragrostis tef), OWB-grazed, and OWB-ungrazed pastures on a sandy clay loam soil. The perennial OWB-legume and native pastures had increased soil organic matter (SOM) and reduced bulk density (ρ_b), improving k, soil water thresholds, λ, and D, compared to annual teff and alfalfa-TW (P < 0.05). Soil λ, but not D, increased with increasing θ_v. Grazed pastures decreased k and water retention compared to other treatments (P < 0.05), yet did not affect λ and D (P > 0.05), likely due to higher ρ_b and contact between particles. Greater λ and D at saturation and PWP in perennial versus annual pastures may be attributed to differing SOM and ρ_b, and some a priori differences in soil texture. Overall, our results suggest that perennial pasture systems are more beneficial than annual systems for soil water storage and heat movement in semiarid regions.