Soil water infiltration and distribution characteristics under different biochar addition amount

Abstract: Biochar is derived from the pyrolysis of biomass, and when buried in soil, it can play the role of long-term soil carbon storage. Evidence suggests that biochar can improve soil fertility and crop production in some circumstances. Aimed to the special double-layer soil structure formed by putting the biochar into the farmland soil, the soil water infiltration characteristics of different addition amounts of biochar (0, 10, 20, 40 and 80 t/hm2) were studied under the condition of ponding infiltration. The study was conducted by the verifying experimental study and model simulation, and combined the laboratory experiment and the field experiment. In field experiment, the field plots were used with the different biochar application rates, the trial was fully randomized with 3 replications, and the biochar was mixed into the topsoil before the soybean was sown. The water distribution model of biochar-soil double-layer soil structure was established and the farmland soil moisture distribution of different addition amounts of biochar in the field was simulated. The results showed that the water infiltration process of biochar-soil double-layer soil structure was composed of 2 nonlinear curves and their slopes were getting smaller. When the wetting front reached the interface between biochar and soil, the infiltration would be temporarily stopped, and the downward water in soil was accumulated on the upper layer until the water content at the interface surpassed 42.5% of the critical water content, which was the time of the turning point of the 2 curves. The soil infiltration rate, the saturated hydraulic conductivity and the critical suction were improved by the addition of biochar, and they were increased by 21.95%-112.20%, 14.29%-52.38% and 13.75%-78.69% respectively when compared with the control group. And the biochar addition also improved the storage capacity and the water content of the upper and lower layers; under the treatment of 80 t/hm2 biochar addition, the water content of the upper layer increased by 35.08%, and the lower layer increased by 13.09%-19.96%. Therefore, the influence of the biochar addition on the upper layer was stronger than that of the lower layer. When the thickness of the upper soil was a constant value of 20 cm, the factor that affected critical suction was only the amount of biochar addition, and the correlation between them was greater than the other 2 infiltration parameters, i.e. the soil infiltration rate and the saturated hydraulic conductivity. Through the verification of the model predictions and field measurements of soil moisture, the distribution regulation of soil moisture can be expressed by the model established in the research under the condition of applying the biochar.