Preparation Of Modified Biochar And Its Effect On Ammonia Volatilization In Soil

Ammonia（NH₃）volatilization is one of the main ways of nitrogen fertilizer loss.In order to deeply understand the influence of biochar on soil ammonia volatilization and tap the potential of reducing soil ammonia volatilization by returning biochar to the field,this study took rice husk and rice straw as raw materials,comparatively analyzed the influence of two modification processes and fifteen modification methods on the basic physical and chemical properties of biochar,studied the modification technology of biochar with emphasis on carboxyl grafting,and tested and analyzed the effect of modified biochar on reducing soil ammonia volatilization,in order to provide reference for the preparation,optimization and establishment of soil ammonia volatilization reduction technology of modified biochar.The main results are as follows:1 The pre-pyrolysis modification（the front of modified）and post-pyrolysis modification（the back-end modification）,as well as ultraviolet irradiation（UV）,microwave（UW）,ultrasonic wave（SW）,tartaric acid（TA）,citric acid（CA）,oxalic acid（OA）,phosphoric acid（PA）,nitric acid（NA）,sulfuric acid（SA）Hydrochloric acid（HA）,potassium hydroxide（PH）,Sodium hydroxide（SH）,hydrogen peroxide（HP）,potassium permanganate（KP）and ferric chloride（FT）were compared and analyzed.The results showed that the p H of the pre-pyrolysis modified biochar was 5.02-8.96,with an average value of 7.05,and that of the post-pyrolysis modified biochar was 3.22-9.75,with an average value of 6.11.The change trend of the p H of biochar under the two technological conditions was consistent.When rice husk and rice husk biochar were used as modified materials,the p H of biochar was significantly decreased by acid modification and magnetic modification,while the p H of biochar was increased by alkali modification and potassium permanganate modification.When rice straw and rice straw biochar were used as modified materials,the p H of biochar was reduced by all modification treatments.The EC value of rice straw biochar is significantly higher than that of rice hull biochar,and other modification methods except physical modification（ultraviolet irradiation,ultrasound and microwave）significantly reduce the conductivity EC of biochar).Alkali modification can significantly increase the content of C element and decrease the content of H element in biochar,among which the content of C element in biochar modified with rice husk at the front of modified changes the most,increasing from 49.31%to 78.78%and decreasing from 34.64%to5.46%.2 The effects of modifier type（oxalic acid,citric acid,tartaric acid）,concentration,modification time and solid-liquid ratio（1:20,1:50,1:70）on the physicochemical properties and carboxyl grafting effect of biochar were studied by orthogonal test.The results showed that the main factors affecting the p H of modified biochar were modifier type>solid-liquid ratio>concentration>time.The main factors affecting carboxyl content are time>modifier type>concentration>solid-liquid ratio.Under the experimental conditions,the optimal parameter combination for preparing carboxyl grafted biochar is 0.3 mol·L^-1 citric acid,and the biochar is modified with the solid-liquid ratio of 1:50 for 4 hours.The physical and chemical properties of carboxyl grafted biochar changed significantly.Among them,the p H of rice husk biochar decreased from 7.84 to 3.32,and the p H of rice straw biochar decreased from 9.90 to 3.51,ash content decreased by 10.62%-19.68%,fixed carbon content increased by 1.54%-12.03%,phenolic hydroxyl content decreased by 1.3%-80%,cation exchange capacity increased by4.9%-31.84%,and carboxyl content increased by 42.4%.3 The effects of biochar and carboxyl-grafted biochar applied to brown soil and saline soil on ammonia emission,soil p H,urea decomposition and alkali-hydrolyzed nitrogen content were observed in laboratory continuous culture experiments.The results showed that the total ammonia volatilization increased by 6.4%and 33.5%in brown soil with biochar compared with that without biochar,and decreased by 19.0%and 16.5%in saline soil compared with that in control.However,carboxyl grafted biochar inhibited ammonia volatilization in both soils.The total amount of ammonia volatilization in brown soil decreased by 40.7%and 39.0%with carboxyl-grafted rice husk biochar and carboxyl-grafted rice straw biochar,respectively,compared with that without biochar,while decreased by 34.1%and 37.4%in saline soil.Is different from most other studies,the purpose of this study was to inhibit ammonia volatilization from brown soil and saline soil,carboxyl grafted biochar with low p H and high carboxyl content was prepared by regulating multiple links and the whole process of modification pathway,it provides reference for the establishment of ammonia volatilization reduction technology in brown soil and saline soil.