Available water capacity of sandy soils as affected by biochar application: A meta-analysis

Sandy soils have inherently low available water capacity (AWC), making their use for agricultural production a challenging task. Biochar amendments have been recommended to enhance the hydrological properties of sandy soils. A meta-analysis of existing literature was conducted to investigate the overall effect of biochar on the AWC of sandy soils. Key factors related to biochar characteristics (specific surface area, particle size, carbon content) and production conditions (pyrolytic temperature, feedstock), soil properties (pH, textural class, organic carbon content), and experimental setting and duration were also included in the analysis. Sandy soils amended with biochar had their AWC significantly increased, on average, by 28.5% compared to un-amended soils. Biochar had no significant effect on AWC when it had a large particle size (PS > 5 mm) or when applied to soils with high carbon content (SOC > 2%). No significant changes in AWC were found among biochar feedstocks, pyrolytic temperatures, and specific surface areas. Available water capacity was higher due to the application of biochar with fine PS compared to coarse PS and with low C (C < 50%) than high C (C > 70%) content. The increase in AWC in biochar-amended sandy soils was most pronounced in those with the highest sand content, acidic pH, and the lowest C content. Our analysis further showed that the effects of biochar application on AWC were greater under controlled laboratory conditions compared to field trials and in short-term rather than in long-term experiments. Overall, the current meta-analysis revealed that biochar technology has the potential to contribute towards the alleviation of the hydrological constraints of sandy soils leading to more drought-resistant soils in the face of an expected dryer climate.