Biochar application enhances soil water storage in wet periods but intensifies drought conditions during dry periods in red soils

Biochar has been widely used for soil carbon storage, reducing gas emissions, controlling soil pollution, and increasing crop production. However, research on the continuous evaluation of soil moisture and soil retention effect following biochar addition, especially in red soils, which are characterized by low porosity, poor infiltration capacity, and seasonal drought, remains limited. In this study, automated soil water content( θ ) and soil matric potential ( ψ ) probes were used to continually explore the differences in θ and ψ between biochar-amended red soils (BC, 65 t ha −1 ) and bare red soils (CK) at 5, 10, 20, 40, and 70 cm soil depths over 3 years. Our results showed that θ at 5 and 10 cm soil depth (biochar-applied layers) significantly increased by 32.00 % and 16.00 % in BC compared to CK, respectively, with even greater increases (33.33 % and 19.23 %) observed during the wet seasons, while decreased by 5.55 % and 4.54 % during the dry seasons (p < 0.05). Soil water storage of 0–5 and 0–10 cm soil depths significantly increased by 30.72 % and 26.48 % under BC, respectively (p < 0.05), though they reduced by 3.32 % and 3.50 % in dry seasons (p < 0.05). On average, available θ in BC was 57.14 % and 25.00 % higher than in CK at 5 and 10 cm depths (p < 0.05), and both decreased by 33.33 % at these depths in dry seasons (p < 0.05). In addition, rainfall conversion efficiency improved significantly by 36.84 % in BC. These findings suggested that water storage capacity and water retention of red soils were enhanced in BC due to their high porosity and water storage capacity. However, soil water storage capacity was significantly reduced in BC during dry periods, potentially due to high soil evaporation and water repellency, and low soil water retention when amended with biochar during these times. • Continuous θ and pF of biochar-amended and bare red soils were evaluated. • θ of surface soils increased in wet periods but reduced during dry periods in BC. • W increased by 2.45 % in wet periods but reduced by 2.05 % during dry periods in BC. • θ a and rainfall conversion efficiency were enhanced after biochar application.