Soil Nitrogen Balance Simulation And Potential Enviromental Risk Assessment In Farmland Ecosystem At County Scale

This paper took Yizheng City,Jiangsu Province and Yujiang County,Jiangxi Province as the case study areas,by using field survey data and laboratory analysis test,locational research and datas of regional study,combined with geostatistic analysis and spatial modeling technology of GIS,the temporal and spatial variability of soil properties,distribution and genesis in different areas were analyzed;and the regional agro-ecosystem apparent nitrogen balance were caculated. Then a regional agricultural soil potential soluble nitrogen model was introduced and verified, which simulated the regional scale of the soil potential soluble nitrogen;Finally the field ecosystem nitrogen potential environmental risk assessment studies were carried out.Results can improve decision-making for application of agricultural nutrients in China.The major conclusions of this study are as fllowed:1)At different times the spatial distribution of soil organic matter(SOM),total nitrogen(TN), soil pH in Yizheng City and Yujiang County had the performance of strong or medium spatial autocorrelation,showing that was affected by regional factors.In 2001 the spatial variability of pH and TN in Yujiang County showed weak spatial correlation,which illustrates a greater impact by human factors.In Yizheng City,the spatial distribution of SOM,TN in three periods and soil pH in 1984 and 2000 tend to is increased from northwest to southeast,and pH in 2004 showed low values in the central part with a small blocks.For Yujiang County,SOM,TN content had a single spatial distribution in 1985;and in 1998 and 2001,the spatial distribution of SOM,TN had a trend of low in middle and high in north-south part;the spatial distribution of soil pH had gradient poor law in all three periods.Totally,SOM,TN increased in most regions during 1984 to 2004 in Yizheng.The soil pH value mainly increased in the northern part,and decreased in southern areas along the river.The SOM and TN in Yujiang County during 1985-2001 are mainly increased in the southern and northern hills regions,soil pH values descresed in most regions.2)The maximum value of the average annual input,output and surplus apparent of nitrogen for cultivated land appeared in Puxi Town located in the southeast corner region along the Yangtze River in Yizheng and Dengbu Town located in river valley plain in Yujiang County.Apparent nitrogen surplus of yizheng City and Yujiang County had a increasing trend during 2000-2005 with a low increase rate.The surplus of the apparent nitrogen of Yizheng City was greater than Yujiang County.The surplus of farmland apparent nitrogen is less than the output in Yujiang County,while it was larger than nitrogen output in Yizheng.This showed that nitrogen accumulated at a high extent in the agro-ecosystems in Yizheng,which has a high potentially riskto the environment.3)By coupling meteorological factors Mode,NLEAP mineralization model,and the apparent nitrogen balance model,a soil potential soluble nitrogen(SPSN) simulation model was established to simulate the nitrogen surplus risk at the regional scale.The simulation results showed that average annual mineralization rate of soil organic matter(SOM) in Yujiang County(mainly in paddy fields) was less than Yizheng City(with a main rotation of rice-wheat),the mineralization of SOM in paddy fields in Yizheng was less than uplands.According to the results by SPSN,the high-value areas of the SPSN content was located in Puxi town on the south-eastern plains along the river in Yizheng city;while Yangxi town located in the southwestern hills and Dengbu Town located in the Tang valley plain in Yujiang county,where were the center town or surrounding towns with developed economies.4)The major factors affecting three main ways of nitrogen losses from farm(run-off losses, leaching losses,gaseous losses) was selected.By using the analytic hierarchy process,the weight factors was decided and the potential environmental risk assessment model based on apparent nitrogen surplus.The evaluation result showed that farmland nitrogen surplus in Yizheng had an a average potential risks.Low-risk areas were mainly located in the southwestern part of Yizheng, high-risk areas are mainly located in the north and the south-east part of Yizheng.The farmland nitrogen surplus in Yujiang was averaged at a lower risk level.The high risk region was in the northeast and southwest part,and the low risk region was in the central part of Yujiang.For the land-use type,the nitrogen loss potential risk of the paddy fields was greater than the uplands.