| The hilly area of the Loess Plateau is a key area for the ecological construction of the two-screen and three-zone in China.The ecological restoration of degraded grassland in this area has attracted the attention of many scholars and local governments.Appropriate ecological restoration measures are of great significance to the ecological restoration and construction of degraded grassland in this area.In order to study the effects of different ecological restoration measures on soil properties and soil quality of grasslands,a study had been done to investigate the different of 0-40 cm soil layer of soil physical properties,aggregates,chemical,biological characters and assessment of soil quality under different restoration measures in the typical steppe of the hilly region of the Loess Plateau in Ningxia in 2015 to 2017,we selected different year old enclosure,contour trench,fish-scale pits(1,3,6,10,15 year respectively)and grazed(as a reference)grassland.The main research conclusions are as follows:(1)Soil fractal dimension has been increasing in enclosure and contour trench with the recovery year,while it showed a up-down trend under fish-scale pits.In the similar recovery years,the volume percentages and fractal dimension of clay and sand under contour trench and fish-scale pits were all higher than those of enclosure.Vertically,variation of soil particle composition was not obvious.The volume percentage is positively correlated with the fractal dimension.(2)The soil bulk density showed a trend of decline with the enclosure year,while it showed a trend of down-up-sown under contour trench and fish-scale pits,but the water holding capacity and porosity were the opposite.the soil bulk density was relatively limited.In the similar recovery years,soil bulk density were the highest in fish-scale pits,the water holding capacity and porosity are close to each other at 3 and 15 year,and the other years were the highest in enclosure.Vertically,there was no significant change in soil bulk density,water holding capacity and porosity under different measures.(3)The destruction rate and fractal dimension showed a downward trend with the enclosure year.Fractal dimension of the mechanical stability aggregates under contour trench and fish-scale pits showed a down-up trend,while the water-stabilized aggregate fractal dimension was opposite.In the similar recovery years,fractal dimension of mechanical agglomerates was the lowest in fish-scale pits,the destruction rate of water-stable aggregates and agglomerates was the lowest in enclosure.Soil MWD and GMD were the highest in enclosure except for 10 years.(4)The aggregate carbon of all grades of soil showed a contour trench>enclosure>fish-scale pits as a whole;the aggregate nitrogen was the highest in enclosure,while contour trench and fish-scale pits were similar.Vertically,carbon and nitrogen contents of soil aggregates at all levels decrease as the soil layer deepens.(5)Soil organic matter,total nitrogen,available nitrogen,total phosphorus,and available potassium increased with enclosure year,while they all showed a trend of up-down-up under contour trench and fish-scale pits measures.In the same age period,soil nutrients have been the largest in enclosure.The soil nutrient content decreased as the soil layer deepened.(6)Soil C/N showed enclosed>fish-scale pits>contour trench,organic carbon and total nitrogen density and storage were all showed enclosed>grazing>fish-scale pits>contour trench.Vertically,C/N under the enclosure is significant,and the organic carbon density decreases as the soil layer deepened.(7)The carbon holding capacity and holding rate of soil showed a fish-scale pits>enclosure>contour trench,while nitrogen holding capacity and holding rate showed a fish-scale pits>contour trench>enclosure.Vertically,the variation of carbon(nitrogen)holding capacity and holding rate under different measures were different.(8)The total amount of soil microorganisms,bacteria and actinomycetes increased under various measures,but there was no obvious change of fungi.In the same age period,the total amount of microorganisms,actinomycetes,and fungi have been the highest in enclosure,while bacteria have different patterns of change between different measures.Vertically,the total amount of microorganisms,actinomycetes,bacteria,and fungi decreased under different measures,but the number of fungi in grazing grassland increased.(9)Soil microbial biomass carbon and nitrogen showed an increase with enclosure year,while they both showed a up-down-up trend in contour trench and fish-scale pits.In the same age period,microbial biomass carbon and nitrogen contents were the highest in enclosure measures.Vertically,microbial biomass carbon and nitrogen decrease from the surface to the deep layer.(10)The soil sucrase,protease,phosphatase and urease activities were increased with the enclosure year,while they all showed a trend of up-down-up under contour trench and fish-scale pits measures,but catalase activity is contrary to other enzyme activities under different measures.In the same age period,soil enzyme activity was the highest in enclosure measures.Vertically,the soil enzyme activity of surface layer was significantly greater than that of the lower layer.(11)Correlation analysis showed that soil characteristics are closely related to vegetation characteristics.There was a significant positive correlation between vegetation cover with biomass,soil organic matter,available nitrogen,total nitrogen and total microbial biomass.There was a significant positive correlation between above ground biomass with organic matter and available nitrogen,while above ground biomass and cover were significantly negatively correlated with soil bulk density.(12)The soil quality scores showed that F15>F10>S15>F6>Y15>F0>S3>Y3>F3>S10>Y10>S1>Y1>S6>Y6.The soil quality in recent years was enclosed>horizontal ditch>Fish scale pit.Based on the changes in soil properties and soil quality,the study concluded that the appropriate grassland ecological restoration measures in the experimental area were enclosed. |
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