Water hydraulics, retention and repellency; response to soil texture, biochar pyrolysis conditions and wetting/drying

Abstract

. Studies which evaluated the aggregation effects in biochar-amended soils by determining the saturated hydraulic conductivity and water repellency, in combination with wetting/ drying scenarios are rare. Therefore, the objective of this study is to link water repellency and water retention in biochar-amended soils to the aggregation effect under different pyrolysis conditions and soil textures. Two feedstock sizes; twig and branch-based mango were pyrolysed at 550°, and were then mixed with sandy loam and silt loam at application rates of; 0, 30, 45 and 60 g kg –1 respectively. Sequentially, the soil-biochar mixtures were subjected to five wetting and drying cycles. In each of the cycles, the saturated hydraulic conductivity, and thereafter the contact angles of the soil-biochar mixtures were measured using the sessile drop approach. The results showed that biochar addition decreased the saturated hydraulic conductivity in all cycles. The rigidity effect was more pronounced in soil amended with biochar and produced using twig mango as opposed to the biochar produced using mango branch. A higher rigidity value was measured in the silt loam and sandy loam amended with twig as compared to the branch-based mango which may be attributed to aggregation processes. This also coincides with higher contact angle values and water retention values that were measured using twig as opposed to branch-based mango.