| Xinjiang is located in the northwest inland arid area.There are a large number of saline-alkali soils in the area.The soil salt content is higher than that of other soils,and the soil fertility is low.The high salt content in the soil affects the transformation of nitrogen nutrients,resulting in low nitrogen fertilizer utilization rate.Because saline-alkali land is an important strategic land for agricultural development in Xinjiang in the future,it is of great significance to study the characteristics of nitrogen migration and transformation in saline-alkali soil for agricultural economic development and land improvement in Xinjiang.Based on the actual situation of salinealkali soil in Xinjiang,this paper adopts the technical route of combining experimental research,theoretical analysis and numerical simulation.The soil water and nitrogen migration law and nitrogen transformation process with different salinization degrees were mainly studied.The results are as follows:(1)The infiltration characteristics of saline-alkali soil in Xinjiang were studied.The infiltration model and wetting front migration model considering the influence of soil salt content were established.In the infiltration model,the soil salt content and the parameter K conformed to the logarithmic relationship,and the soil saft content and the index a conformed to the linear relationship.In the wetting front migration model,the soil salt content and the coefficient A conformed to the linear relationship,and the soil salt content and the index B conformed to the logarithmic relationship.At the same time,the wetting front migration distance and cumulative infiltration of sullate-chloride saline-alkali soil were ranked from large to small:moderate salinesaline soil 1>severe saline-alkali soil>saline soil 2>saline soil 3.The salt in the soil migrates with the water to the deep soil.At 5 cm,the soil salt content of the moderate saline-alkali soil is 64.5%lower than the background value,the severe saline-alkali soil is 69.7%lower than the background value,the saline soil 1 is 78.9%lower than the background value,the saline soil 2 is 81.65%lower than the background value,and the saline soil 3 is 90.8%lower than the background value.Soil nitrogen mainly migrates in the form of nitrate nitrogen.At the end of infiltration,nitrate nitrogen in moderate saline-alkali soil and severe saline-alkali soil is mainly distributed at 45 cm.Nitrate nitrogen in saline soil 1 is mainly distributed at 0-35 cm.Nitrate nitrogen in saline soil 2 is mainly distributed at 0-25 cm.Nitrate nitrogen in saline soil 3 is mainly distributed at 0-15 cm.In the redistribution process,due to soil mineralization,the content of ammonium nitrogen in soil profiles with different salinization degrees was gradually higher than the initial value.Due to the high salinity of saline soil 2 and saline soil 3,the mineralization was inhibited,and the content of ammonium nitrogen in soil profiles was higher than the initial value.(2)The characteristics of nitrogen transformation in saline-alkali soil were revealed,and the kinetic models of mineralization,nitrification and ammonia volatilization under the influence of soil salt content were constructed.Under certain salt conditions,low salt promoted mineralization and nitrification,while high salt inhibited mineralization and nitrification.The peak values of net mineralization rate and net nitrification rate of sulfate-chloride saline-alkali soil were ranked in the order of severe saline-alkali soil>moderate saline-alkali soil>saline soil 1>saline soil 3.The ammonia volatilization accumulation and ammonia volatilization rate of different saline-alkali soils increased with the increase of soil salinization degree.The apparent nitrogen loss rates of sulfatechloride type saline-alkali soils were 10.75%(salt content 18.3 g/kg),12.23%(salt content 25.5 g/kg),38.63%(salt content 42.2 g/kg)and 69.31%(salt content 165 g/kg),respectively.The apparent nitrogen loss rates of chloride-sulfate type saline-alkali soils were 9.68%(salt content 4.86 g/kg)and 31.6%(salt content 31.37 g/kg),respectively.The fitting coefficient a in the ammonia volatilization kinetic model was logarithmically related to the soil salt content.In the kinetic model of mineralization and nitrification,the potential mineralization potential and potential nitrification potential have a power function relationship with soil salt content,and the mineralization rate constant and nitrification rate constant have a quadratic function relationship with soil salt content.(3)A model of water and nitrogen migration and transformation in saline-alkali soil under nitrogen application was established.The hydraulic characteristic parameters and nitrogen migration parameters of soil with different salinization degrees were determined.Under the condition of potassium nitrate application,the actual values of soil cumulative infiltration,wetting front migration distance,ammonium nitrogen and nitrate nitrogen content were well fitted with the simulated values,and the R2 was greater than 0.885.Based on the inversion parameters,the migration and transformation process of water and nitrogen in saline-alkali soil under the condition of ammonium sulfate application was simulated.The order of cumulative infiltration and wetting front migration distance of soil with different salinization degrees was the same as that under the condition of potassium nitrate application.During the infiltration process,under the condition of ammonium sulfate application,the soil ammonium nitrogen was collected at 0-20 cm,while under the condition of potassium nitrate application,the ammonium nitrogen content changed little,and the nitrate nitrogen was collected at 45 cm.When potassium nitrate was applied,the nitrate nitrogen content of moderate saline-alkali soil at 45 cm was 800 mg/kg.Under the condition of potassium nitrate application,the nitrate nitrogen content of moderate saline-alkali soil at 45 cm was 2800 mg/kg,which was much larger than that of ammonium sulfate application,and it was easy to cause soil nitrogen leaching. |
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