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A meta-analysis on biochar's effects on soil water properties – New insights and future research challenges

Edeh, Ifeoma G., Mašek, Ondřej, Buss, Wolfram
The Science of the total environment 2020 v.714 pp. 136857
application rate, biochar, clay, clay soils, coarse-textured soils, drought, field capacity, meta-analysis, particle size, porosity, runoff, sand, sandy soils, saturated hydraulic conductivity, soil texture, soil water, soil water retention, surface area, water content, wilting point
Biochar can significantly alter water relations in soil and therefore, can play an important part in increasing the resilience of agricultural systems to drought conditions. To enable matching of biochar to soil constraints and application needs, a thorough understanding of the impact of biochar properties on relevant soil parameters is necessary. This meta-analysis of the available literature for the first time quantitatively assess the effect of not just biochar application, but different biochar properties on the full sets of key soil hydraulic parameters, i.e., the available water content (AWC), saturated hydraulic conductivity (Kₛₐₜ), field capacity (FC), permanent wilting point (PWP) and total porosity (TP). The review shows that biochar increased soil water retention and decreased Kₛₐₜ in sandy soils and increased Kₛₐₜ and hence decreased runoff in clayey soils. On average, regardless of soil type, biochar application increased AWC (28.5%), FC (20.4%), PWP (16.7%) and TP (9.1%), while it reduced Kₛₐₜ (38.7%) and BD (0.8%). Biochar was most effective in improving soil water properties in coarse-textured soils with application rates between 30 and 70 t/ha. The key factors influencing biochar performance were particle size, specific surface area and porosity indicating that both soil-biochar inter-particle and biochar intra-particle pores are important factors. To achieve optimum water relations in sandy soils (>60% sand and <20% clay), biochar with a small particle size (<2 mm) and high specific surface area and porosity should be applied. In clayey soil (>50% clay), <30 t/ha of a high surface area biochar is ideal.