Effects Of Biochar Types And Amounts On Hydraulic Characteristics Of Typical Subtropical Soils

The soil in subtropical region of China is"dry,thin,sticky and sour",which ser iously restricts the sustainable development of agriculture and economy in the whole region.The burning of agricultural and forestry wastes into biochar can not only imp rove the comprehensive utilization rate of wastes,but also repair and improve the soi l,which is of great significance for agricultural production in subtropical areas.Base d on three typical soils of red soil,paddy soil and aquic soil in subtropical region,t his paper studied the effects of different application amounts of rice husk biochar,w ood chip biochar and bamboo biochar(0,0.5%,1%,3%,5%)on soil hydraulic c haracteristics through laboratory experiments,and quantitatively analyzed the relationsh ip between different application amounts of biochar and soil water movement paramet ers.To elucidate the mechanism of biochar in soil improvement,and provide scientifi c basis for reasonable selection of biochar in different soil improvement and guiding the application amount of biochar.The main conclusions are as follows:(1)Different types of biochar mixed with different soil texture,the effects of different soil moisture characteristics.The effect of rice husk biochar on water holding capacity of red soil and paddy soil was the most obvious.The water holding capacity of red soil with 3%rice husk biochar was the strongest,and the water holding capacity of paddy soil with 5%rice husk biochar was the strongest.Bamboo biochar had the most significant effect on water holding capacity of aquic soil,and the water holding capacity was the strongest under 5%bamboo biochar treatment.The results showed that adding high content of rice husk biochar(3%,5%)had the best improvement effect on water holding capacity of red soil and paddy soil,and adding 5%of bamboo biochar had the best improvement effect on water holding capacity of aquic soil.The low content of rice husk biochar(0.5%,1%)weakened the water holding capacity of the three soils,while the high content of rice husk biochar enhanced the water holding capacity of the three soils.(2)Different types of biochar mixed with different soil texture have different effects on pore structure and water constant.The influence of biochar on the pore structure and water constant of red soil was greater,while the influence on paddy soil and aquic soil was slightly smaller.Add biochar high content were significantly improved the three kinds of soil saturated moisture content(p<0.05).The addition of biochar had no obvious effect on the available water content of red soil,but the addition of 5%rice husk biochar had the largest available water content,and the addition of higher(5%)biochar significantly increased the available water content of paddy soil and aquic soil(p<0.05),and the improvement effect of5%sawdust biochar on the available water content was the best.The results showed that adding high content of biochar could effectively increase soil available water content.(3)The addition of rice husk biochar sharply reduced the saturated water conductivity of the three kinds of soil,while the addition of wood chip biochar and bamboo biochar had a certain fluctuation in the saturated water conductivity of the three kinds of soil.With the increase of biochar content,the unsaturated hydraulic conductivity of red soil increased firstly and then decreased.The addition of biochar could decrease the unsaturated hydraulic conductivity of paddy soil and aquic soil,and the unsaturated water conductivity and water diffusion decreased first and then tended to be flat or slightly increased with the increase of biochar content.The rice husk biochar had the greatest influence to the unsaturated hydraulic conductivity of soil ability,bamboo biochar,wood biochar minimal impact.(4)The infiltration characteristics of biochar mixed with soil of different texture are significantly different.The three kinds of biochar all have inhibition effect on red soil infiltration,and rice husk biochar has the greatest effect on red soil infiltration process,and5%rice husk biochar treatment has the strongest inhibition effect on red soil infiltration.Biochar can enhance the infiltration capacity of paddy soil,and the effect of low biochar content on water infiltration of paddy soil is stronger than that of high biochar content,and the addition of 0.5%wood biochar treatment has the greatest promoting effect on water migration of paddy soil.The inhibition effect of 5%rice husk biochar on soil water infiltration was the greatest,while the promotion effect of 3%wood chip biochar was the best.Model fitting results show that the Horton model after biochar soil water infiltration process applied to the optimal fitting effect,second Kostiakov model,Philip model fitting effect is the worst.(5)The water conductivity parameters of red soil and paddy soil treated with biochar showed a high correlation with their pore distribution,which showed a significant or high degree of negative correlation with micro pores(p<0.05),and an extremely significant or high degree of positive correlation with macropores(p<0.01).The initial permeability f_i,steady permeability f_cand decay index k of red soil treated by biochar are highly correlated with water constant and pore distribution.The infiltration parameters of paddy soil treated with biochar have little or no significant correlation with the pore distribution,which indicates that the change of pore structure has little influence on the infiltration characteristics of paddy soil,and other factors have greater influence.There was a significant or high negative correlation between hydraulic parameters and water constant of aquic soil treated by rice husk biochar and bamboo biochar(p<0.05).