Effects of carbon on moisture storage in soils of the Wisconsin Central Sands, USA

Quantifying soil water storage is important for plant growth and agricultural production. This is particularly important in sandy soils because they are widely cultivated and prone to drought. We investigated the effect of soil organic carbon (SOC), soil texture and gravel content on soil moisture characteristics in sandy soils. Soil moisture characteristics were analysed using standard soil physical characterization as well as visible–near infrared (vis–NIR) spectroscopy and pedotransfer functions (PTFs). Volumetric water content (−10, −33, −1500 kPa) and available water capacity (AWC) increased by 0.01 to 0.02 m³m⁻³ with a 2% increase in silt plus clay content. Available water capacity increased by about 0.05 m³m⁻³ with a 1% increase in SOC. A 5% increase in gravel in the subsoil decreased the volumetric water content of the soil by 0.01 m³m⁻³. Predictions of volumetric water contents and AWC by vis–NIR were the best when using a random forest model. Pedotransfer functions for AWC predictions performed best when sand, silt, clay, bulk density and SOC were included. Soil moisture storage ranged from 44 to 65 mm in the top 50 cm. At mean evapotranspiration (4.2 mm day⁻¹), irrigation requirements were reduced by 6 days in the sandy soils that have larger SOC and silt contents in the topsoil. These soils are sandy throughout but have subtle differences in particle‐size distribution, SOC concentrations and gravel content. These differences affect soil moisture storage considerably. Soil management practices that increase the SOC contents in these sandy soils favour moisture storage and tend to reduce irrigation requirements. HIGHLIGHTS: SOC, soil texture and gravel affect soil moisture characteristics in sandy soils. With vis–NIR and PTFs, soil water storage, water characteristics and AWC in soils with >80% sand can be quantified and predicted. Available water capacity increased by about 0.05 m³m⁻³ with a 1% increase in SOC. Subtle differences in particle‐size distribution affect soil moisture storage and reduce irrigation requirements.