Study On Nitrogen Conversion Process In Jinghuiqu Irrigated Area

Nitrogen is a necessary element for plant growth.a large amount of nitrogen fertilizer used can increase crop yield and effectively solve the problem of food security caused by less cultivated land per capita.At the same time,the current situation that global warming and the groundwater nitrate pollution caused by the residual mineral nitrogen cannot be ignored.The problem of high grain yield and environmental security has become an irreconcilable contradiction.And Jing Huiqu irrigation area is the main grain production base of guan zhong plain.In recent years,the activities of irrigation and fertilization have resulted in excessive nitrate levels.But what's the effect on nitrogen transformation in vadose zone for irrigation caused by irrigation and rainfall is unknown up to now.and the effects on process and mechanism of transformation of nitrate in the soil have also been unclear yet.Therefore,it is of great significance to study the nitrogen conversion process in irrigation area,whether from agricultural production and environmental protection,or theory and method.Based on the truths that farmland ecosystem in the Jing Huiqu irrigation district was regarded as study area and vadose zone in the area as the research medium,this paper will study the regularity,using ¹⁵N isotope tracer technique and Markov Chain Monte Carlo numerical analysis model,the ecological effect of nitrogen transformation model,of nitrogen transfer,as well as the response of the effects on process for nitrogen conversion by factor of ecological environment through the indoor,field plot and the combination of field irrigation experiment means.This paper mainly draws the following conclusions:1.The process of nitrogen transfer in the irrigation area has been dominated by mineralization,nitrification,microbial assimilation.The gas belt will eventually show a large accumulation of nitrate through Remineralization and nitrification although the rate of mineralization and microbial assimilation was significantly lower than that of nitrification.The phenomenon which the rate of nitrate production is greater than the rate of consumption,resulting in nitrate leaching and denitrification gas loss,can cause the risks of greenhouse gases generation and groundwater nitrate pollution while The assimilation and dissimilation reduction of nitrate are not obvious.2.Within the irrigation area,the rates of NH₄⁺-N adsorption,nitrification,denitrification,mineralization,microbial assimilation,NH₃ volatilization all have a tendency to decrease with the increase of depth.and the conversion rate threshold value range also has a tendency to decrease with increasing depth.3.The main ecological factors affecting the adsorption of NH₄⁺-N in the whole irrigated zone were ammonium nitrogen content and volume moisture content,which were positively correlated with NH₄⁺-N adsorption rate.The effect of ammonium nitrogen content on NH₄⁺-N adsorption was significant in the range of 2²0mg/kg.The volume moisture content is beneficial to the adsorption of NH₄⁺-N between 0.2 and 0.4.And the ammonium nitrogen content and soil temperature as the main influencing factors of nitrification rate were positively correlated with the rate of nitrification.The obvious effects on the rate of nitrification in the ammonium nitrogen content of the threshold from 3 to 14mg/kg,ground temperature threshold for between-10 and 30?;The main ecological factors that affect the microbial assimilation rate are the total number of microorganisms and geothermal temperature.Total number of microorganisms of assimilation rate is significantly influenced in the range from 0 to 10⁵,and temperature threshold between-10 and 30?.In the threshold range,both factors were positively correlated with the microbial assimilation rate.The main ecological factors affecting denitrification rate in the vadose is denitrifying bacteria.And it's significant for denitrification rate that the number of denitrifying bacteria in the range from 0 to 7.5×10⁴.Volume moisture content and geothermal temperature are the main ecological factors affecting mineralization.The volume moisture threshold,which range is from 0 to 0.12,is positively correlated with the mineralization,and negative correlation was found between 0.12 and 0.30.Ground temperature between 5 and 18?are positively correlated with the mineralization rate,but negatively correlated while the threshold is from18 to 32?.The main ecological factors affecting NH₃ volatilization rate are geothermal and volume moisture content.NH₃ volatilization rate in shallow vadose zone is significantly influenced by the geothermal threshold between 10 and 27?and volumetric moisture content threshold from 0.32 to 0.42 while both had no significant influence on it in the deep range.