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ARS Home » Plains Area » Bushland, Texas » Conservation and Production Research Laboratory » Livestock Nutrient Management Research » Research » Publications at this Location » Publication #115389
Title: Soil hydraulic properties of cropland compared with reestablished and native grassland

Author
item Schwartz, Robert
item Evett, Steven - Steve
item UNGER, PAUL - USDA-ARS, RETIRED

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2002
Publication Date: 9/1/2003
Citation: Schwartz, R.C., Evett, S.R., Unger, P.W. 2003. Soil hydraulic properties of cropland compared with reestablished and native grassland. Geoderma 116:47-60.

Interpretive Summary: Tillage alters the soil properties that influence water movement. Likewise, reestablishment of grass on cropland will, over time, produce changes in soil properties that can influence the amount of plant available water. A study was conducted to characterize and compare soil hydraulic properties on adjacent native grassland, cropland, and Conservation Reserve Program (CRP) sites at three locations in the Texas High Plains. Steady state infiltration rates at a tension were measured to evaluate saturated and unsaturated water flow in soils. Soils were sampled to determine bulk density and water retention properties. Saturated hydraulic conductivities measured on sweep-tilled cropland soils were no different than saturated conductivities on grassland soils. However, average unsaturated conductivities of cropped soils were four times greater than grassland soils. CRP sites had the lowest saturated hydraulic conductivities, which suggests that, after 10 years, grasses had not fully improved changes in pore structure caused by tillage. Results of a 10-day simulation of evaporation from a bare soil suggest that the larger unsaturated conductivities measured for sweep-tilled cropland leads to increased evaporative losses of water as compared with grassland, CRP sites, and no-tillage cropland. These results suggest that tillage can reduce the amount of water available for plant growth and that precipitation use efficiency increases slowly over time after cropland is replanted to perennial grasses. Lastly, land use practices had a greater effect on water movement than did soil series. Thus, the characterization of soil hydraulic properties solely based on soil type may lead to poor assessments of precipitation use efficiency.

Technical Abstract: Reestablishment of grass on cropland will, over time, produce changes in soil hydraulic properties that can influence the amount of plant available water. We conducted a study to characterize and compare soil hydraulic properties on adjacent native grassland, cropland, and Conservation Reserve Program (CRP) sites at three locations in the Texas High Plains. A tension infiltrometer was used to measure unconfined, unsaturated infiltration ove a range of water tensions (0.05, 0.5, 1.0, and 1.5 kPa) at the soil surface. Intact soil cores were sampled within the Ap and Bt horizons to determine bulk density and water desorption curves, theta(h). Unsaturated hydraulic conductivity over the range of tensions K(h) was estimated using Wooding's equation for steady state flow from a disc source. The van Genuchten-Mualem model was simultaneously fitted to K(h) and theta(h) data to obtain parameter values for each land use treatment. Mean near-saturated dhydraulic conductivities of cropland were not significantly different from grassland. However, at 1.5 kPa supply tension, cropped soils had a mean unsaturated conductivity four times greater than grassland. CRP sites had the lowest (P < 0.05) near-saturated hydraulic conductivities, which suggests that, after 10 years, grasses had not fully ameliorated changes in pore structure caused by tillage. Results of a 10-day simulation of evaporation from a bare soil suggest that the larger unsaturated conductivities measured for sweep-tilled cropland leads to increased evaporative losses of water as compared with other land uses. Lastly, land use practices had a greater effect on water movement than did soil series. Thus, the characterization of soil hydraulic properties solely based on soil type may lead to poor assessments of precipitation use efficiency.