Effects Of Biochar On Physicochemical Properties And Characteristics Of Water And Nutrient Adsorption And Transport In Soil

Excessive fertilization?especially nitrogen fertilizer?and high-intensity continuous cropping are common phenomena in vegetable production in China,which lead to nutrient imbalance and soil degradation,and the ability of water and fertilizer conservation and the effect of vegetable yield increase are significantly reduced.In order to cope with the growing food demand and reduce environmental pollution in the future,it is of great significance for the sustainable development of vegetable planting industry to improve the properties of vegetable soil and its water and fertilizer retention capacity.Biochar has the advantages of rich carbon,high porosity,large specific surface area,high surface charge and strong stability.When applied to the soil,it can reduce soil bulk density and acidity,increase soil porosity,improve soil water holding and fertilizer retention,and reduce water and nutrient leaching.However,different types of biochar and the rate of biochar applied have different effects on different soil properties.Whether biochar can play a positive role in the remediation and improvement of vegetable soil as an soil amendment,and which biochar and the rate of biochar applied are more suitable for the improvement of vegetable soil,there are few relevant studies at present.Therefore,rice husk biochar?RB?and palm silk biochar?PB?were used as soil amendments in this paper.They were applied to vegetable soil at rates of 0,3%and 6%.They were recorded as Control,RB1,RB2,PB1 and PB2,respectively.Through the indoor short-term soil incubation experiment,NH₄⁺-N adsorption experiment and soil infiltration and leaching experiment,the effects of two types of biochar and different application rate on soil physicochemical properties,water infiltration characteristics and nitrogen and phosphorus nutrient adsorption and transport characteristics were analyzed respectively.The main conclusions of this paper are as follows:?1?Biochar could significantly affect the physical and chemical properties of soil,and the degree of influence was related to the type of biochar,the rate of biochar applied and the time of biochar has applied.Biochar can decrease soil bulk density and saturated hydraulic conductivity,and increase soil total porosity and water holding capacity.Biochar decreased soil acidity,and the effect of biochar on soil nutrients was mainly related to its own nutrient content at the early stage of applying,and the higher the rates of biochar,the more significant the increase of soil nutrient content.With the extension of application time,biochar significantly inhibited soil nitrification and decreased nitrogen availability.?2?Biochar can change soil water infiltration characteristics,and the effect is different under different infiltration conditions?infiltration head 1 cm,1 cm+fertilizer,4 cm?.Biochar can decrease the infiltration capacity of sandy loam,and the higher the rate of biochar applied,the more obvious the effect.Under the same treatment and different infiltration conditions,the infiltration capacity of soil is different,which were in turn of 4cm>1 cm>1 cm+fertilizer.The cumulative infiltration and the wetting front of the treated soil all conform to the power function relationship with time,And Kostiakov infiltration model can well simulate the cumulative infiltration curve of biochar amendment soil with time.?3?The adsorption capacity of soil to NH₄⁺-N was significantly improved with the increase of biochar addition.The Langmuir isotherm adsorption model can better simulate the NH₄⁺-N adsorption curve of biochar amendment soil,and the maximum adsorption capacity?S_m?of each treatment was in turn of PB2>RB2>RB1>PB1>Control.The correlation analysis showed that the adsorption capacity of NH₄⁺-N was positively correlated with soil p H and organic matter content.?4?The results of leaching experiment showed that with the increase of biochar applied,the cumulative leaching volume significantly decreased,and the electric conductivity increased.The rates of 6%biochar addition could increase the p H value of the leachate.The rates of 3%biochar addition can significantly reduce the DOC cumulative leaching,with the increase of biochar applied,the DOC cumulative leaching increased,and RB at rates of 6%had no significant effect on the DOC cumulative leaching of soil,which is related to the higher DOC content of biochar itself.?5?Nitrogen in soil is more easily leached than phosphorus,and biochar can effectively alleviate the leaching rate of nitrogen and phosphorus in soil.Two kinds of biochar in the leachate,and the content of NO₃^--N was lower.Biochar significantly increased the proportion of DON and decreased the proportion of NH₄⁺-N in the leaching solution.After leaching,the NH₄⁺-N content of soil profile increased with the increase of soil depth,and the NH₄⁺-N content of soil treated with biochar was higher than that of Control.The amount of TP,TDP and MRP in the leachate decreased with the increase of biochar application.With the increase of leaching times,the proportion of MRP to TP increased gradually,and the proportion of DOP to TP decreased gradually.TDP was the main form of phosphorus in the leachate,accounting for 79.2%?94.1%of TP,while PP accounted for 6.7%?21.2%of TP.Applyinging biochar significantly increased the proportion of PP and DOP in the total leachate and decreased the proportion of MRP,Thus,the availability of phosphorus in the leachate decreased,this is conducive to alleviating the water pollution caused by nutrient leaching.After leaching,available phosphorus content in soil profile increased first and then decreased with the increase of soil depth.Compared with Control treatment,available phosphorus content decreased in the biochar amendment soils.