Research On Physical And Chemical Characteristics And Evaluation Of Soil Quality In Hunan Northwest District

Research on physical and chemical and biological characteristics of rocky desertification soil in the process of dynamic change rule, we can know different grade rocky desertification of the basic characteristics of the soil and soil quality change rule, which has great significance on the vegetation restoration and repair of ecological environment on rocky desertification area. Hunan northwest land counts for area of 21233.73 km2, the karst area of 7986.56 km2, rocky desertification area of 2485.04 km2, potential rocky desertification area of 3599.98 km2. Rocky desertification made soil degradation in the region, land productivity decline, and the deterioration of ecological environment. This study combined with the national forestry public welfare industry special scientific research project "evergreen broad-leaved forest restoration research offices, rocky desertification area", in the northwest of Hunan rocky desertification areas, according to the potential rocky desertification (evergreen broad-leaved forest, the comparison), mild, moderate, severe and extreme five rocky desertification grade, we select Longshan, Cili, representative sample to 13 in the concession for investigation of vegetation and soil investigation, and collect 65 soil samples,the determination of soil physical, chemical and biological properties index of 23, we intends to explore changes of these indexes in the process of the succession of rocky desertification and the relationship between each other, at the same time, using the principal component analysis, factor analysis, minimum data set and fuzzy mathematics method to establish the rocky desertification area of soil quality evaluation index system of soil quality index, method is used to evaluate the soil quality of rocky desertification area. Main conclusions are as follows:l)The soil physical property indexes in the process of rocky desertification succession characteristics:bulk density is compact, from 1.07 g·cm3 (potential rocky desertification) to 1.38 g·cm3 (extremely severe rocky desertification).Capillary moisture capacity, capillary porosity and total porosity have the same change trend of consistent overall declining, soil is from potential rocky desertification stage to extremely severe rocky desertification stage, while the three is from 46.51%,47.41% and 59.59% respectively, to 31.51%,40.82%,50.14%.In terms of soil mechanical composition, soil succession from potential rocky desertification stage to extremely severe rocky desertification stage, clay (< 0.002 mm) and coarse powder (0.05～0.02 mm) composition changes smoothly, changing by 40.41%,12.20% to 39.90%,9.00% respectively; While fine powders (0.02-0.002 mm) and sand (2～0.05 mm) the composition of the present change alternately, fine powder grain composition level decreased from 32.79% to 19.10%, and coarse grain composition level increased from 9.62% to 28.00%.2)The chemical properties of soil index in the process of rocky desertification succession characteristics:variations in acid and alkaline soil present after the first acid alkali features. In the succession of rocky desertification, soil pH remains acid (5.92～6.85) and has fluctuated; When soil by severe rocky desertification succession to extremely severe rocky desertification, soil pH rises, weakly alkaline (7.39).The soil organic matter content is present a strictly monotone decreasing trend, reducing from potential rocky desertification stage 59.00 g·kg-1 to extremely severe rocky desertification stage 22.94 g·kg-1.Soil total nitrogen, total phosphorus content show first after descending trend. The change of the total potassium content is of volatile, high point in severe rocky desertification stage (16.39 g·kg-1) and low point in moderate rocky desertification stage (13.33g·kg-1).The change of effective potassium content fluctuation is bigger also, high point in potential rocky desertification stage (148.52 mg·kg-1) and low point severe rocky desertification stage (101.59 mg·kg-1). Effective phosphorus content begins to decline from potential rocky desertification stage of 2.76 mg·kg-1 to mild rocky desertification stage of 0.25 mg·kg-1, and then maintains steady. The change rule of soil cation exchange capacity is consistent with the rule of effective potassium. In the mild rocky desertification and severe rocky desertification two phase, cation exchange capacity are the biggest,which are 33.47 cmol·kg-1 and 31.73 cmol·kg-1, respectively.3)The variation characteristics of soil microbial indexes:the microbial biomass carbon has decreased from 112.36mg·kg-1(potential rocky desertification) to 26.68mg ·kg-1(extreme severe rocky desertification). The microbial biomass nitrogen has fluctuated slightly in the succession of rocky desertification, but its value at extreme severe rocky desertification holds the line with that in potential rocky desertification; the change of microbial biomass phosphorus fluctuates significantly with no obvious regularity. The change of soil microbial biomass C/P and C/N demonstrates wave of diminishing, both of them decreased from 34.30 and 9.32 to 13.05 and 2.66. Total bacteria number is closely related to organic matter content, and its value appears a decline trend, decreases from 4650cfu·g-1 (potential rocky desertification) to 673.5cfu ·g-1 (extreme severe rocky desertification).4)The correlation analysis of 23 indicators between physical, chemical and microbial properties demonstrates:organic matter content is very significant correlated to total porosity, sand, coarse slit, fine slit and natural water capacity; density is very significant correlated to capillary porosity;total porosity is very significant correlated to fine slit and sand;sand is very significant correlated to coarse slit,fine slit and natural water capacity;fine slit is very significant correlated to coarse slit and natural water capacity;organic matter content is very significant correlated to total nitrogen,available phosphorus and CEC.The intersectional correlation analysis between all of indicators shows:CEC is very significant correlated to density and capillary porosity;available potassium is very significant correlated to total bacteria.5)The Minimum Data Set of soil quality evaluation of northwest area of Hunan has been established after 10 referential indexes being selected from 23 soil quality evaluation criterions, by measures of principal component analysis(PCA), variance analysis(VA) and etc., which are pH, organic matter, total phosphorus, microbial carbon, microbial nitrogen, microbial phosphorus, C/P, total bacteria, capillary moisture capacity and sand grain(2-0.05mm).6)The consequence of soil quality index(SQI) shows, the SQI of potential rocky desertification is highest(0.36), in turn,0.30(mild rocky desertification), 0.27(moderate rocky desertification),0.19(severe rocky desertification) and 0.16(extreme severe rocky desertification). The above demonstrates that the change direction of soil quality stage is completely consistent with the succession of rocky desertification, and there demonstrates a periodic serious degradation when soil turned from potential rocky desertification to mild and moderate rocky desertification. However, there shows a very severe degradation in the succession from moderate rocky desertification to extreme severe rocky desertification.