The Dynamics And Transfer Of Soil Organic Carbon And Nitrogen In The Scenario Of Erosion And Aridity In The Loessial Region

It is well known that aridity and erosion are the severe issues impacting agriculture andecoenvironment on the Loess Plateau. Aridity directly influences on arable land productivityand the dynamics of soil organic carbon(SOC) and nitrogen. In order to control soil and waterlosses and improve ecoenviroment on the Loess Plateau, the conversion of slope farmland tograssland and forestland has been carried out. More attention was paid to restoration ofvegetation and the protection of natural vegetation. In the scenario of aridity and erosion, theprocesses of restoration of vegetation and types of vegetation exert significant influence onthe changes in SOC and nitrogen in these lands.The studies were conducted to investigate the SOC changes in arable dryland, grasslandand forest land, to examine the impacts of vegetation restoration process on SOCaccumulation, mineral nitrogen transfer and distribution in soil profile, the loss process of soilorganic matter and nitrogen in the loessial slope by the means of taking soil samples,analyzing soil samples and field monitoring. The objectives were to understand themechanism of the influences of fertilization, vegetation restoration and types of vegetation onSOC pools and mineral nitrogen transfer in soil profile, to determine relationships betweensoil organic matter and nitrogen losses and slope length or slope gradient. The goals of thesestudies were to work out the measures to improve soil fertility, to raise nitrogen use efficiency,to control soil nutrient losses, to evaluate capacity of SOC sequestration in arable land,grassland and forestland, and to demonstrate the soil carbon storage and its effect onecoenvironment. The results of this thesis were summarized as followings:(1) Dynamics of Soil organic carbon pool in arable lands in different areasII The Dynamics and Transfer of Soil Organic Carbon and Nitrogen in the Scenario of erosion and aridity in the LoessialRegionon the Loss PlateauFertilization management has the close relation to the dynamics of soil organic carbon(SOC) pool in arable lands in Yangling, Changwu and Ansai. Application of nitrogenfertilizer, combination of nitrogen and potassium fertilizer or combination of phosphorus andpotassium fertilizer had no significant effect on SOC sequestration and accumulation.However, application of combination of nitrogen and phosphorus fertilizer or combination ofnitrogen and phosphorus and potassium fertilizer could significantly promote SOCsequestration and storage. Furthermore, application of manure of combination of nitrogen,phosphorus and potassium fertilizer could significantly increase SOC sequestration andstorage fast. The rate of SOC sequestration and storage demonstrated the order ofYangling>Changwu>Ansai. Soil microbial biomass carbon(MBC) had the significantcorrelation with SOC in the arable land in these three regions. MBC also had the significantcorrelation with soil microbial biomass nitrogen. These suggested that size of microbialbiomass and the level of soil nitrogen had been increase the raise of SOC, which was benefitto improve soil fertility and enforce soil nutrient cycling.(2) The driving effect of vegetation on the dynamics of SOC pool and themechanismThe contents of SOC and the sizes of MBC declined with the increase of soil depth in therestored grasslands with different history. The level of SOC and the sizes of MBC in thetopsoil rose with increase in length of conversion. The size of MBC demonstrated thesignificant correlation with the size of MBC, and the rotio of MBC to SOC increased the riseof level of SOC, which suggested that the size of MBC could indicate the trend of SOCevolutioninthe restored grasslands.In the scenario of arid or semiarid environment, planted Caragana could raise the level ofSOC and the size of MBC in the topsoil. MBC had the significant correlation with SOC, andthe ratio of MBC to SOC declined with the increase in soil depth in the soils grown withdifferent kinds of fo...