[Effects of biochar addition on soil moisture infiltration process of the yellow soil in Karst area].

To investigate the effects of biochar addition on soil moisture infiltration characteristics of sloping farmland in Karst area, we used soil column simulation to study the variation characteristics of cumulative infiltration volume, infiltration rate, and wetting peak process under the different biochar addition amount (0, 1% and 2%) and different particle sizes (<0.25, 0.25-1 and >1 mm), and simulated the infiltration process in yellow soil on slope farmland. The results showed that soil infiltration process after biochar addition was significantly inhibited under the condition of constant bulk density. The cumulative infiltration amount and infiltration rate under biochar addition were significantly lower than those without biochar addition. There was no significant difference in the cumulative infiltration amount and infiltration rate of the soil with 1% and 2% biochar addition. The cumulative infiltration amount of the soil with different particle sizes followed an order of <0.25, 0.25-1 and > 1 mm after biochar addition. When the addition amount was 1%, the cumulative infiltration amount of 300 min had decreased by 20.9%, 35.2% and 45.0% compared with CK. When the addition amount was 2%, the decrease rate was 21.5%, 37.5% and 44.2%, indicating that the inhibition effect of large particle size biochar on soil infiltration being stronger than that of small particle size biochar. The change trend of soil wetting peak process to biochar addition of different contents and different particle sizes was consistent with the change trend of cumulative infiltration volume. Horton model and Kostiakov model could be used to simulate soil moisture infiltration process. The Horton model had higher fitting accuracy, the largest R² (between 0.91 and 0.98), and the smallest RMSE (between 0.14 and 0.21). The initial infiltration rate obtained by Kostiakov model was closer to the measured result. Our results could provide scientific basis for the rational application of biochar and provide a useful reference for soil improvement and soil and water conservation in slope farmland of Karst area.