Factors affecting water retention in biochar-amended soil

Biochar is a stable carbon-rich material produced from carbon-rich biomass in the absence of air or under oxygen-limited conditions.  A plethora of feedstocks can be used to produce biochar including wood-based materials, organic wastes (i.e. sludges, manure), plant-based materials (i.e, leaves, seeds, husks) as well as food-waste residues or by-products.  In addition, pyrolysis conditions such as temperature, heating rate, duration and the scale the pyrolysis system, also vary considerably. Therefore, biochars differ widely in their physical and chemical characteristics. Biochar is recommended as a soil amendment due to its ability to enhance the physicochemical characteristics of soil and support crop growth.

Biochar influences soil in various ways. It can raise pH, enhance cation exchange capacity, increase extractable nutrients, modify microbial communities and soil processes, and improve physical traits like bulk density and structure, supporting better plant growth. This study reviews the factors that influence the interaction of soil and biochar in terms water retention. The analysis shows that biochar generally reduces soil bulk density and improves water retention, especially in coarse‑textured soils where field capacity, wilting point, and available water increase substantially. Effects are smaller in medium soils and minimal in fine soils.