Effect Of Biochars And Ultrasonic-modified Biochars On The Nutrient Cycle Of N,P And The Migration And Transformation Of Pollutants In Pb Contaminated Soil

In agricultural production,in order to meet the rising demand of agricultural products caused by population growth,applying excessive amount of nitrogenous fertilizers is very common to increase the gain yields.However,excessive application of fertilizers would likely to cause to a series of environmental issues,such as soil acidification,water eutrophication,greenhouse effect and heavy metal pollution.Biochar typically possesses a range of effective surface characteristics,such as large specific surface area and pore volume,which could enhance the biochar capacity for retention of nutrients and sorption potentially toxic elements and organic pollutants.And ultrasonic techniques could improve the function of raw biochar by enhancing its physicochemical properties and sorption capacity.The cavitation effect induced by ultrasonic waves would exfoliate and break apart structural layers of biochar,which may dramatically affect the porosity,permeability and physical adsorption of biochar.In our study,a 1:10?w/v?ultrapure water suspension of the dead pig biochar and Platanus orientalis biochar was modified by ultrasound for 40 min at25 ^oC,200 W.The influence of ultrasonic modification on the physicochemical properties of raw biochars was determined,the aim of our study was to assess the effect of different biochars on leaching loss of NH₄⁺-N and NO₃^--N in in biochar treated soil and on the fractions of P from the soil-plant system,to evaluate the effect of different biochars on the yield and quality of water spinach and the fractions of Pb in the soil-plant system.The main conclusions are as follows:1.The physicochemical properties of biochar is depending on the species of raw materials.The animal-derived biochar?dead pig biochar?had higher alkalinity and cation exchange capacity and richer oxygen-containing functional groups and mineral elements.And the presence of phosphate was detected in the surface of dead pig biochar.The plant-derived biochar?Platanus orientalis biochar?had larger surface area than the animal-derived biochar.Ultrasonic modification could play a positive role in improving the pH,EC,CEC and specific surface area of biochar,while may have little effect on the oxygen-containing functional groups and element composition of biochar.2.Biochar is generally comprised of relatively recalcitrant forms of N.We have observed a significant decrease in inorganic N?NH₄⁺-N and NO₃^--N?leaching between the biochar and control treatments.And the animal-derived biochar addition to soil played a comparatively lower part in inhibiting mineral N?especially NO₃^--N?leaching loss than the plant-derived biochar.Significant differences in the leaching losses of inorganic N species were not observed under the UPB treatment.After the pyrolysis production,most of P in dead pig biochar is bioavailable,which could increase the available P of water spinach in the soil-plant system by combined application of dead pig biochar and fertilizer.Significant rises in the inactive P?HCl-P and Res-P?were determined with Platanus orientalis biochar application,which was proved to have little influence on Olsen P in soil.Ultrasonic modification of dead pig biochar would play an essential role to further enhance the acceleration of Olsen P from the soil.3.Compared with the control,the increase of dry matter weight and the decrease of chlorophyll derived from the water spinach with dead pig biochar addition to soil was determined.Ultrasonic-modified dead pig biochar could significantly enhance the content of soluble sugars in the water spinach.In particular,the combined application of biochar and fertilizer could promote the increase of dry matter weight,chlorophyll and soluble sugar from the water spinach in the soil treated with biochar or fertilizer alone.All biochars treatments significantly reduced the availability of Pb in the soil and the content of Pb in the water spinach,relative to the control.The inhibition of exchangeable Pb and Pb bound to Carbonates and the promotion of residual Pb were detected in dead pig biochar treated soil.Whether ultrasonic modification was employed or not for biochar,the amount of Pb in the soil-water spinach system did not differ significantly.Hence,as a soil conditioner,dead pig biochar and Platanus orientalis biochar could enhance the nutrient retention capacity in soil by reduce inorganic N leaching and improve N availability.And dead pig biochar could also be used as a P addition to increase the yield and quality of crops.After dead pig biochar and Platanus orientalis biochar addition,available Pb in soil was significantly decreased,which provide a possible method for the remediation of the Pb contaminated soil.