Effects Of Stimulated Nitrogen Deposition And Cutting On Physical-Chemical Properties On Soils And Microbial Biomass In A Typical Steppe In Inner Mongolia

This study was conducted with 0-10cm soil as the experimental material, which is the root system dense level of steppe's plants, has more soil microbial biomass, has higher soil microbial active degree in the area Xilinhaote in Inner Mongolia. Research effects of stimulated nitrogen deposition with manual work fertilizer N and cutting on physical-chemical properties on soils including soil moisture content, soil pH value, soil total C content and soil total N content, and soil microbial biomass C and N in the typical steppe in Inner Mongolia through continuous 11 months experimental conduction. Furthermore, determine the plants' root biomass on the basis of the relevant between soil microbial biomass and plants' root biomass. Probe into the variation tendency of physical-chemical properties on soils and soil microbial biomass on the atmospheric nitrogen deposition setting, be aimed at providing the credible theoretical testimony for the high yield, dependable crop and high quality of pasture in Inner Mongolia.This study set 4 different process mode with Fertilizing every month and no cutting (FMNC), Fertilizing every month and cutting (FMAC), Fertilizing half of one year and no cutting (FYNC) and Fertilizing half of one year and cutting: (FYAC). Every process mode set 6 different fertilizing N level with CK, T1, T3, T10, T20 and T50, represent different atmospheric nitrogen deposition repectively with 0,1,3,10,20,50 g N·m-2·a-1, every process mode set 3 repeat. The results showed as follows:1. Stimulated nitrogen deposition with manual work fertilizer N and cutting conduction reduce soil moisture content. For every gradient fertilizing N and cutting, the lowest soil moisture content is the critical value of the steppe plants needing N for growing, not the conduction with the most or the lowest fertilizing N. For the conduction which haven't cut, the steppe vegetation has smaller mass growth and needing N, the critical value of needing N bring forward. So, the herdsman should increase the pasture stubble when they cut, in the same time reduce the more soil moisture content evaporation capacity for strong solar radiation and create drought of surface layer, make use of N from atmospheric nitrogen deposition as much as possible, promote the growth of pasture, improve the output of pasture. 2. Soil pH-value increased at the low N-treated treatments (T1 and T3) and decreased at the high N-treated treatments(T10 , T20 and T50) in FMNC, FYNC and FYC; In FMAC, soil pH-value increased at T3 and T10, and decreased at T1, T20 and T50. That impressed the high N-treated decreased soil pH-value. Every conduction of different gradient fertilizing N, along with the increasing fertilizing N capacity, the soil pH value has obvious variation tendency, increase first and decrease then, and increase again at last when soil pH value decrease to minimum.So, in the area with more atmospheric nitrogen deposition, it should increase the coverage rate of the steppe vegetation as much as possible, take effective measures to decrease the proper overland part biomass of the steppe vegetation, promote the steppe vegetation to intake N from atmospheric nitrogen deposition as much as possible, transfer N, prevent excessive N accumulate in soil and lead to reduce soil pH value.3. All of the total soil C and N decreased at all of N-treated in FMNC and FYNC except at T10 in FMNC; And diversification trend of the total soil C and N was not significant in FMAC and FYAC, on the whole, both of them have lower the total soil C and N than CK. In soil, it has the fixed C/N ratio, it effects the variation tendency of the total soil C content and reduce the effective soil C content when increase the total soil N content, because in Inner Mongolia, the total soil C content mainly come from decomposing of overland part of the steppe vegetation. Excessive cutting reduce decomposer, prevent the C from being into soil, and reduce the total soil C content, on the contrary, it effects the effective intake on the vegetation to N, lead to run off of N. So, the herdsman should improve certain decomposer for grassland when they cut, promote the source of C, balance soil C/N ratio.4. Soil microbial biomass C and N decreased at T20 and increased at other N-treated in FMNC. In FMAC, FYNC and FYAC, soil microbial biomass C and N decreased at all of N-treated except soil microbial biomass N increased at T20 in FMAC. The result demonstrated that nitrogen deposition can decrease growth and reproduce of soil microorganism, The level at T20 can most significantly decrease soil microbial biamass C and N.5. The root weights at all of the N-treated treatments decreased in FYNC and FYC; And at the lower N-treated treatment increased a bit in FMNC and FMC, N-treated was not significantly correlated with the root weights. We found that the root weights increased firstly and then decrease, at the last increased with N-treated, the variation tendency of the root weights is same to the variation tendency of the soil pH value. Because vegetation is a coordination entirety, the growth of the plant overland part is intimate to the development of the root underground part, the study prove at the same time, it is possible that lower N promotes the growth of the vegetation roots, and asks the herdsman to take effective measures to reduce the total soil N, on conditional that increased atmospheric nitrogen deposition, it is the only way to increase the growth biomass of vegetation, make use of the vegetation roots to transfer the soil N. So, in the area of steppe, it is necessary to control the hight and frequency of cutting.