Comprehensive Soil Quality Evaluations Of Inner-mongolia Typical Grassland Under Different Management Modes

Grassland ecosystem in the world accounts for 46%of the total terrestrial land area,and China grassland ecosystem is the largest land ecosystem,mainly distributed in Inner mongolica plateau.At present,the serious soil degradation of grassland in Inner Mongolia is the most important ecological problem faced with China.To realize the great potential of grassland ecology and production function,and to carried out the research on different utilization ways and management measures of grassland,has become a hot spot to improve grassland ecological environment.Based on the typical steppe xilingol grassland in Inner Mongolia,the soil nutrients(organic carbon,total nitrogen,total phosphorus and total potassium),physicochemical property(pH and conductivity),microelement(Na,Fe,Mg,Ca,Mn,Bo,Si),heavy metal element(As,Cd,Cr,Hg,Ni,Pb,Zn),and GRSP content of four soil samples(0-5 cm?5-10 cm?10-20 cm?20-40 cm)were measured in three management modes samples(grazing gradient,enclosure and fire management).Interrelationship of each index was explored by stepwise regression analysis,PCA and RDA analysis.Structural change of GRSP under different management was analyzed by using the scanning electron microscope and infrared spectroscopy.Contribution of GRSP to grassland soil was discussed.Meanwhile,the soil quality in different management patterns was evaluated by means of geoaccumulation index(Igeo)and total potential ecological risk index of heavy metals(RI).Management mode and intensity adopted in grassland soil recovery were discussed by establishing mathematical model and simulating the grassland management scene analysis.Our results showed that:(1)Soil nutrient changes:There was a significant negative correlation(P<0.01)between the grazing intensity and total organic carbon,nitrogen,phosphorus and potassium content and the conductivity in soil,and a positive correlation between grazing intensity and pH value.Total organic carbon,nitrogen content in soil were increased(P<0.05)by low intensity of grazing(1.5 sheep per hectare).Burning treatment decreased soil organic carbon content between 0-5 cm,while increased that between 10-40 cm(P>0.05).Quadrennial burning treatment significantly increased the soil organic carbon content compared to biennial treatment.Enclosure treatment significantly increased the soil organic carbon content(P<0.05),while no significant change was found in total nitrogen and potassium content(P>0.05).Organic carbon and total nitrogen content in enclosed sample soil 33a were slightly lower than that in enclosed sample soil 13a(P>0.05).(2)Changes in heavy metal and trace elements:Influence of different grassland management modes to trace elements mainly reflected on the increased grazing intensity and enclosed period were the main factors causing the variation of soil trace elements.Effect of variation of firing frequency on soil nutrient was not obvious,but it was the main factor that led to the changing of heavy metal in soil.Under the three management modes,sample soil was regarded as non-pollution when geoaccumulation index(Igeo)<0,and as risk-free when total potential ecological risk index of heavy metals(RI)<150.(3)GRSP contents and its function changes.Influence of different management modes on GRSP mainly reflected on that Low intensity of grazing(1.5 sheep per hectare)significantly increased content of EE-GRSP and T-GRSP.Quadrennial burning treatment significantly increased EE-GRSP content in surface soil(0-5 cm)and T-GRSP content in 0-40 cm soil.Enclosure treatment significantly increased EE-GRSP content in 0-40 cm soil and T-GRSP content in 0-5 cm soil.The surface structure of GRSP in enclosed sample soil 33a reduced to different degrees under high intensity grazing and biennial burning treatment.Grazing,burning and enclosing haven't brought about the variation in functional groups of GRSP,but there was difference in content of functional groups.Stepwise regression analysis showed that nitrogen content in three management modes soil was an important limiting factor influencing the generation and accumulation of GRSP.Different grassland management modes had different effects on GRSP ecological function.GRSP ability in capturing carbon and nitrogen increased under high intensity grazing and quadrennial burning treatment.(4)Comprehensive evaluation and management scenario analysis:Evaluation of soil quality was carried out using the methods of significance and principal component.The results of the two methods are consistent and significant correlation(R2=0.5674-0.7722).However,the method of principal component evaluation was more apt to evaluate the soil quality objectively due to the exclusion of human interference.Management scenario analysis clearly showed that to adopt burning treatment every 3-4 'years and enclosure lower than 30 a,and maintained the moderate grazing intensity at 0?3 sheep per hectare could effectively improved the overall quality of soil more than 2.4-fold.In future,alternate management measures should be carried out to make up for the risk of soil nutrient reduction and heavy metal pollution caused by single management mode,and to ensure the sustainable supply of soil nutrients in the grassland,so as to achieve the goal of improving grassland productivity.