Effect of Biochar Application on Hydraulic Properties of Sandy Soil under Dry and Wet Conditions

Core Ideas High doses of biochar increased water retention of sandy soil in both dry and wet conditions. Larger sized biochar decreased water retention at field capacity (FC). High‐pyrolysis biochar could increase water retention at FC and in dry conditions. We investigated the impact of biochar application on the evaporation rate of sandy soil. Knowledge of soil hydraulic properties under dry (below permanent wilting point) and wet (from saturation to permanent wilting point) conditions is helpful for evaluating soil physical quality and modeling the movement of the substances (water and nutrients) in biochar‐amended soils. To investigate the effect of biochar application on hydraulic properties of sandy soil under dry and wet conditions, water retention in wet conditions and soil drying curves from wet to dry conditions were measured under different application rates (1, 3, and 5%, w/w), particle sizes (<0.25, 0.25–0.5, 0.5–1, and 1–2 mm), and pyrolysis temperatures (300, 450, and 600°C) of wheat ( Triticum aestivum L.) straw‐derived biochar. Results showed that when higher rate biochar (3 and 5%) was applied into the sandy soil, water retention became higher under dry and wet conditions. Biochar application with a larger particle size (0.5–1 and 1–2 mm) increased water retention under saturation and dry conditions but decreased water retention at field capacity. Sandy soil amended with biochar at the higher pyrolysis temperatures (450 and 600°C) had higher water retention under field capacity or dry conditions. Increasing biochar application rate, particle size, and pyrolysis temperature decreased the evaporation rate of sandy soil under dry conditions. Our findings suggested that hydraulic properties of the sand–biochar mixture were mainly determined by biochar properties under dry conditions and were highly related to the interpores between particles under wet condition.