| At present,a series of environmental problems such as air,soil and water caused by nitrogen loss in farmland seriously harm human health and restrict the sustainable and green development of agriculture.In recent years,biochar has been widely recognized as a promising measure for nitrogen fixation and emission reduction.However,there are some problems in its application,such as large amount of biochar and limited emission reduction effect.Therefore,in order to improve the overall benefit of biochar,the effects of nanobiochar on nitrogen adsorption and desorption and leaching were studied in this paper,so as to provide a theoretical basis for field application of nano-biochar to reduce nitrogen loss and improve nitrogen use efficiency.In this study,bulk biochar was prepared from straw stalk,nano biochar was prepared by ball milling method,and the basic physical and chemical properties and structural characterization of bulk biochar and nano biochar were measured.Related studies were carried out through laboratory adsorption and desorption simulation tests and soil column leaching simulation tests.The main research contents and results are as follows:(1)Rice straw biochar was used as raw material to prepare nano-biochar by ball milling method.Basic physicochemical properties and structural characterization of bulk biochar and nano-biochar were determined.The results show that,compared with the bulk biochar,the particle diameter is reduced by about 80%,the pore structure is changed,and the specific surface area is increased by 49.27%.The content of O element increased by 7.9%,while the content of N element decreased slightly.pH is reduced by about 5.4%and alkalinity is reduced.The acidic functional groups of nano-biochar increased by about 6.7%and the basic functional groups decreased by about 8.5%.(2)Laboratory adsorption and desorption simulation tests were conducted to explore the effects of different biochar dosages,different solution nitrogen concentrations,different solution pH values,different adsorption time and different desorption time on the adsorption and desorption of ammonium nitrogen by nano-biochar.Isotherm model and kinetic model were used to fit the test data and simulate the adsorption-desorption process.The results showed that,compared with the bulk biochar,the adsorption and desorption effects of nanobiochar on ammonium nitrogen showed very significant advantages.The maximum adsorption capacity of nano-biochar is 6.91 mg/g,which is twice the adsorption capacity of bulk biochar under the same conditions.The maximum desorption capacity of nano-biochar was 6.051 mg/g,1.9 times that of bulk biochar under the same conditions.The adsorption modes of ammonium nitrogen are mainly monolayer adsorption and chemisorption,and the desorption process can be regarded as the reverse process of adsorption reaction.(3)Laboratory adsorption and desorption simulation tests were conducted to explore the effects of different biochar dosages,different solution nitrogen concentrations,different solution pH values,different adsorption time and different desorption time on the adsorption and desorption of nitrate nitrogen by nano-biochar.Isotherm model and kinetic model were used to fit the test data and simulate the adsorption-desorption process.The results showed that nano-biochar showed significant advantages in the adsorption and desorption of nitrate nitrogen compared with the bulk biochar.The maximum adsorption capacity of nano-biochar for nitrate nitrogen is 5.985 mg/g,which is 2.2 times of that of bulk biochar under the same conditions.The maximum desorption capacity of nano-biochar was 5.578mg/g,2.6 times of that of bulk biochar under the same conditions.The adsorption methods of nano-biochar for nitrate nitrogen are mainly monolayer adsorption and chemisorption,and the desorption process can be regarded as the reverse process of adsorption reaction.(4)Soil column leaching test was carried out to explore the influence of adding different propotions of bulk biochar and nano-biochar on the related indexes of soil leaching solution.The results showed that the two kinds of biochar could increase the soil pH and EC value of soil leaching solution,and decrease the volume of leaching solution,the concentration of ammonium nitrogen and nitrate nitrogen,but the effect of nano-biochar was more significant.When both bulk biochar and nano-biochar were added at 5.0%,the cumulative leaching loss of NH4+-N in soil leaching solution was the lowest,which was 13.05%and 39.22%lower than that in CK treatment,respectively.When the addition ratio of bulk biochar and nano-biochar was 3.0%and 5.0%,respectively,the cumulative leaching loss of NO3--N in soil leaching solution was the lowest,which was 3.75%and 43.26%lower than that in CK treatment,respectively.Nano-biochar showed significant advantage in reducing nitrogen leaching loss.In The above results showed that compared with bulk biochar,nano biochar showed significant advantages in nitrogen adsorption-desorption effect.The maximum adsorption capacity and desorption capacity of nano-biochar for ammonium nitrogen were 6.91 mg/g and 6.051 mg/g respectively.The maximum adsorption capacity of nano-biochar for nitrate nitrogen was 5.985 mg/g,and the maximum desorption capacity was 5.578mg/g.When the proportion of nano-biochar was 5.0%,the cumulative leaching loss of NH4+-N and NO3--N in soil leaching solution was the lowest,which was 39.22%and 43.26%lower than that in CK treatment,respectively.This study can provide new ideas and guidance for the efficient development of biomass resources,and has important practical significance for promoting efficient utilization of water and nitrogen resources and reducing agricultural non-point source pollution. |
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