Effect Of Revegetation On Soil Organic Nitrogen Mineralization In Southern Mountain Area Of Ningxia

The southern mountain area of Ningxia belongs to the transitionzone of the Loess Plateau to the arid sandy area, the poor stability of the ecological environment, the lack of water resources, soil erosion and desertification, the ecological environment has been greatly damaged. In view of this, the measures of returning farmland to forest and grassland were adopted to improve soil condition. But in the process of vegetation restoration, the mineralization of soil nitrogen in different vegetation types, and the dynamic change of the labile organic nitrogen components are still not clear.Therefore,the situ method was used in mountain area of Southern Ningxia restored grassland(natural grassland, artificial grassland,natural recovery grassland(fallow) and three plantation(Caragana korshinskii, Prunus davidiana, Prunus armeniaca) to determine soil nitrogen transformation rate(net mineralization rate, net ammonification rate, net nitrification rates and microbial nitrogen fixation rates), organic nitrogen and labile organic nitrogen contents(particulate organic nitrogen and light fraction organic nitrogen, soluble organic nitrogen and microbial biomass nitrogen) content in cultured for 0.5a, 1a, 1.5a and 2a.At the same time the plantation(Caragana korshinskii, Prunus davidiana), grass(Stipa bungeana, alfalfa) and land(corn) of indoor temperature and humidity mineralization simulation experiment, cultivate 56 d to research the same index.Finally, adding exogenous 15 N labeled glycine incubation experiment,and determine the plantation(Caragana korshinskii, Prunus davidiana), grass(Stipa bungeana,alfalfa) and land(corn) in soil ammonium nitrogen, nitrate nitrogen and microbial biomass nitrogen in the culture within a week of content and isotopic element abundance changes.In order to reveal soil mineralization processes of organic nitrogen mineralization and mineral biological nitrogen fixation pathway, the characteristics and their mutual relationshipunder different vegetation types in mountainous area of Southern Ningxia, for the vegetation restoration measures of implementation and provide a theoretical basis, seek a scientific,effective vegetation restoration approaches.The main conclusions are as follows:⑴ Incubation 56 d soil particulate organic nitrogen and microbial biomass nitrogen content increased by 1.4% ~ 13.1% and 11.3% ~ 114.9%, light fraction organic nitrogen and dissolved organic nitrogen content decreased by 20.8% ~ 56.4 % and 9.4% ~ 22.7%in eachvegetation type soil. Compared with the wild-situ culture 1a and 1.5a, particulate organic nitrogen and dissolved organic nitrogen content increased 3% to50% and 4% to 100%,respectively, light fraction organic nitrogen and soluble organic nitrogen reduced by 30% to70%; in spring buried the tube outer tube particulate organic nitrogen in the soil, when dissolved organic nitrogen and microbial biomass nitrogen ratio fall to take up pipe soil content of 0.2% to 0.3%, 0.1% to 0.9% and 0.1% to 0.7%; particulate organic nitrogen content in situ culture 2a tube soil increased 4% to 100% than the tube outer soil, and microbial biomass nitrogen content contrary culture 2a tube soil above the pipe outer soil 2%to 100%; light fraction organic nitrogen culture 0.5 a tube content is higher than the soil outside the tube 10% to 100%.⑵Soil organic nitrogen content in vegetation types showed particulate organic nitrogen(0.33 g / kg)> light fraction organic nitrogen(0.16 g / kg)> microbial biomass nitrogen(0.03 g / kg)> soluble organic nitrogen(0.02 g / kg); incubation process natural grassland particulate organic nitrogen and light fraction organic nitrogen content was significantly larger than the other plots, and dissolved organic nitrogen and microbial biomass nitrogen difference in the respective plots were not significant. Field training process of natural grassland and woodland Mountain Peach particulate organic nitrogen and soluble organic nitrogen was significantly higher than the other plots, Caragana woodland microbial biomass nitrogen content was significantly higher than in other plots.⑶Mineralization processes in laboratory incubation 56 d was more active in culture 0 ~7 d, net ammonification rate as low as-0.06 ~-0.38 mg /(g · d), and then remove Prunus davidiana forest and other plots of corn farmland microbial nitrogen fixation rates of up to0.40 ~ 2.07 mg /(g · d), in culture 8 ~ 14 d net ammonification rate up 0.11 ~ 0.23 mg /(g · d),caragana land hickory woodland and grassland natural microbial nitrogen fixation rate minimum-0.15 ~-1.10 mg /(g · d); soil net mineralization and net nitrification rate in culture while the maximum 0 ~ 7 d, 0.43 ~ 1.17 mg /(g · d) and 0.50 ~ 1.23 mg /(g · d), respectively.⑷Caragana woodland microbial biomass nitrogen content was significantly higher than in other plots, which is conducive to microbial holding role. Soil nitrogen net mineralization and net nitrification rate in caragana land was significantly higher than other plots, artificial grass, grass intercropping significantly lower than other plots; contrary Soil nitrogen net ammonification rate in the korshinskii woodland low. Field situ culture exhibits abandoned land soil net nitrogen mineralization rate and net ammonification rate is higher than the artificial turf 0.002 mg /(g · d) and 0.007 mg /(g · d), and net nitrification rate low 0.005 mg /(g · d), compared to artificial grassland vegetation restoration, restoration of abandoned natural way is to maintain and enhance effective measures for soil fertility. Mineralization inthe study area is greater than the microbial nitrogen fixation, soil mineralization and nitrification in the main, is the use of microbial mineral nitrogen in ammonium.⑸Add soil exogenous glycine in culture 0.5 h,1.4% conversion to ammonium nitrogen,2.6% and 4.8 % is converted to nitrate and microbial biomass nitrogen; ammonium-15 N culture 12 h accounted ammonium nitrogen a ratio of 4.7% was significantly higher than other culture period, accounting for nitrate nitrate-15 N ratio of 8.7% was significantly higher than at other times; conversion ratio of indoor culture week after the glycine nitrate(5.2%)>microbial biomass nitrogen(3.0%)> ammonium nitrogen(1.4%), the soilof the study area is larger than ammonification nitrification microorganisms and solid support role, accumulation of inorganic nitrogen in nitrate-based.