Biochar Effects on Wet and Dry Regions of the Soil Water Retention Curve of a Sandy Loam.

Reported beneficial effects of biochar on soil physical properties and processes include decreased soil density, and increased soil water transport, water holding capacity and retention (mainly for the wet region). Research is limited on biochar effects on the full soil water retention curve (wet and dry regions) for a given soil and biochar amendment scenarios. This study evaluates how biochar applied to a sandy loam field at rates from 0 to 50 Mg ha⁻¹ yr^–1 in 2011, 2012, or both years (2011+2012) influences the full water retention curve. Inorganic fertilizer and pig slurry were added to all treatments. Six months after the last biochar application, intact and disturbed soil samples were collected for analyses. Soil water retention was measured from −1 kPa to −100 kPa using tension tables and ceramic plates and from −10 MPa to −480 MPa using a Vapor Sorption Analyzer. Soil specific area was estimated from the dry end water retention data. Biochar tended to increase water retention in the matric potential range of −1 kPa to −100 kPa Significant increases in water content consistent with biochar rate was observed for −10 MPa to −100 MPa for all application scenarios (2011, 2012, and 2011+2012). Although a similar trend of increased water retention was observed from −100 MPa to −480 MPa, there was little difference among the different biochar rates. Increases in soil specific surface area for biochar treatments were consistent with rates and slurry application. Apparent hysteresis of the dry region-water retention curve increased with increasing biochar rates.