Study On Cultivated Land Quality Evaluation Based On Microbial Diversity

The protection of the quantity,quality and ecology of cultivated land is closely related to the national food security,ecological security and social stability.Therefore,the quality of fertility,environment and health of cultivated land has attracted wide attention of scholars.At present,the assessment of cultivated land quality in China generally focuses on the monitoring of physical and chemical properties and organic and inorganic pollution indicators,and seldom includes soil microbial indicators.Soil microbial biomass and diversity play a key role in the decomposition of soil organic matter and nutrient cycling.It is particularly important to include microbial biomass and diversity in the monitoring indicators of cultivated land quality and to evaluate the ecological quality of cultivated land.In this study,47 monitoring sites of cultivated land in Gaoyao District were selected as the research objects.The physical and chemical properties,microbial biomass and structural diversity of the hilly areas in northern Gaoyao District,central Plain Region,Eastern Plain Region and southern Hilly Region were analyzed.The spatial heterogeneity and interrelationship of each index were discussed,and the evaluation index system of cultivated land soil ecological quality was constructed.The main results are as follows:(1)Through semi-variogram fitting model,it was found that the nugget value/base value of soil in Gaoyao area was less than 25%except p H,CEC,DOC and organic matter,and the spatial autocorrelation of other physical and chemical indexes was weak,which was greatly influenced by human factors.Soil p H value ranges from4.28-8.15,clay content 6.03-63.71%,organic matter content 17.20-48.80 g·kg^-1,CEC content 3.97-33.74 cmol⁺·kg^-1,DOC content 1.14-222.45 mg·kg^-1,total nitrogen content 0.30-2.85 g·kg^-1,alkali-hydrolyzed nitrogen content 61.60-246.40 mg·kg^-1,total phosphorus content 0.55-2.85 g·kg^-1,available phosphorus content 3.70-45.55mg·kg^-1.Soil CO₂emission was 21.58-809.09 mg·kg^-1.It can be seen that the nutrient content of soils in Gaoyao District is relatively rich,and most of them meet the national secondary standards.(2)By fitting the semi-variogram model of PLFA of soil microbial flora,it was found that PLFA of microbial flora in high-key areas had obvious spatial variability,nugget value/base value were more than 50%,and spatial autocorrelation was weak,which was greatly influenced by human factors.The content of bacteria was3.02-35.00 nmol·g^-1,the content of Gram-positive bacteria was 1.13-13.70 nmol·g^-1,the content of Gram-negative bacteria was 0.74-10.30 nmol·g^-1,the content of fungi was 0.25-4.50 nmol·g^-1,the content of arbuscular mycorrhizal fungi was 0.06-1.03nmol·g^-1,the content of actinomycetes was 0.59-5.97 nmol·g^-1,the total PLFAs was3.95-46.50 nmol·g^-1,and the ratio of Gram-negative bacteria was 1.30-2.05.The ratio of bacteria to fungi ranged from 3.34 to 12.94.(3)Through Kriging interpolation method,the spatial distribution map of each index is obtained,and each index has obvious spatial heterogeneity.By comparing the results of Kriging interpolation,it was found that there was a significant spatial correlation between organic matter,alkali-hydrolyzed nitrogen,soil CO₂release and the ratio of bacteria to fungi,the ratio of Gram-positive bacteria to Gram-negative bacteria,which was decreasing from the northern hilly area to the eastern plain area to the central plain area and the southern hilly area.(4)According to correlation analysis and co-inertia analysis,the correlation between organic matter,alkali-hydrolyzed nitrogen and soil CO₂release and microbial community structure was further confirmed.At the same time,the ratio of microbial bacteria to fungi,Gram-positive bacteria to Gram-negative bacteria were suggested as good indicators of soil microbial diversity in regional cultivated land quality evaluation.(5)The results of principal component analysis showed that there were significant differences in cultivated land quality between Gaoyao northern hilly area,central plain area,eastern plain area and southern hilly area.In summary,the microbial indicators are greatly influenced by human factors because of the perennial cultivation of cultivated land.There is no obvious correlation between the spatial distribution of PLFA and soil physical and chemical indicators,but the ratio of bacteria to fungi(B/F),the ratio of Gram-positive bacteria to Gram-negative bacteria(G⁺/G^-)and the physical and chemical properties(such as organic matter,alkali-hydrolyzed nitrogen,etc.).The obvious spatial correlation indicates that soil microbial structure is related to soil fertility,which can be used as one of the ecological indicators for monitoring cultivated land quality.The results of this study can provide some reference value.Of course,more and more detailed research and exploration are needed in the future,so as to improve the system of cultivated land quality monitoring and make it develop in the direction of dynamic,diversified and comprehensive.