Effect of Calcareous Concretion on Soil Water Retention Curve and Available Water Content in Calcic Vertisol.

Soil water retention curve (WRC) is one of the most important properties in soil hydraulic studies. Current studies normally focus on fine soils, ignoring the water holding capacity of coarse fragments (>2 mm) and their effects on soil available water content (AWC). Calcareous concretion (CC) is a kind of coarse inclusions that distributed widely in agricutural soils around the world. This study was conducted to quantify the effects of proportion and size of CCs on soil WRC and AWC of a calcic vertisol. The WRCs of CCs were measured using the sand box and ceramic plate method, and the WRCs of fine soils and soil-CC mixtures of various sizes (2-5 mm, 5-8 mm, and 8-30 mm) and proportions (5%, 10%, 15%, and 30% on total mass basis) of CC were determined using the centrifuge method. The WRCs were fitted with the van Genuchten equation. The results showed that CCs maintained considerable amount of water. The saturated water contents of CCs of 2-5 mm, 5-8 mm and 8-30 mm were 0.251, 0.220 and 0.196 cm³ cm^-3, respectively. Addition of CCs changed the WRC and pore distribution of soils significantly. The AWCs of soil-CC mixtures were decreased with increasing CC content. A linear equation, which included the fraction of CC and water content in CC, was proposed to estimate the AWC of soils containing CCs accurately. Accounting for calcareous concretions in the calcic vertisol improved the accuracy of soil hydraulic property estimation and led to a better field water management.