Soil Properties And Quality Evaluation Under Different Vegetation Restoration And Soil Covering Thickness In Pisha Sandstone Area

As the ecological environment is fragile and soil erosion is very serious in the Pisha sandstone area.A large amount of sediment is imported into the Yellow River every year.The control of soil erosion has long been one of the problems faced by our country.Many scholars have carried out a lot of work on ecological restoration and soil erosion in the Pisha sandstone area,which has significantly improved the ecological environment of the area.However,the soil erosion in the Pisha sandstone area is still very serious,and the artificial forest is gradually degraded,species regeneration is difficult,the quality of treatment still needs to be improved.The ecological degradation of the Pisha sandstone area in Ordos City is serious.Therefore,based on the needs of vegetation restoration and reconstruction,ecological construction,governance and development in the Pisha sandstone area,this study takes the soil of different artificially restoration vegetation and natural restoration grassland in the loess-Pisha sandstone junction as the research object.Determine soil physical(sand particles,silt particles,clay particles,bulk density,moisture),chemical(p H,organic matter,total nitrogen,total phosphorus,available nitrogen,available phosphorus)and biological properties(enzyme activity),analyze the differences in soil properties under different vegetation restoration,and the distribution of soil properties in the study area.Finally,the minimum data set(MDS)and the weighted TOPSIS method were used to evaluate the soil quality in the study area.The results show that:(1)The improvement effect of the four kinds of artificially vegetation on soil water content was better than that of the natural grassland in the control group.The soil water content of Pinus tabulaeformis was highest,which was significantly different from that of other four kinds of vegetation(P<0.05),compared with the natural grassland,it increased by55.23%.Under the restoration of Pinus tabulaefolia vegetation,the proportion of soil clay particles was larger,the bulk density was smaller,the water content was higher,and the improvement of soil physical properties was the best,followed by Hippophae rhamnoides.In terms of nutrients and enzyme activities,Pinus tabulaeformis and Hippophae rhamnoides have the best improvement effect.On the whole,under the restoration of Pinus tabulaeformis and Hippophae rhamnoides,organic matter content increased by 34.27 % and43.12 %,total nitrogen increased by 42.11 % and 78.95 %,ammonium nitrogen increased by46.15 % and 25.64 %,and nitrate nitrogen increased by 42.22 % and 69.44 %,respectively.Therefore,compared with natural restoration of grassland,artificial restoration of Pinus tabulaeformis and Hippophae rhamnoides significantly improved soil organic matter,total nitrogen,available nitrogen,and enzyme activity,while the phosphorus level was lower than that of natural restoration of grassland.In the vertical direction,litter input has obvious improvement effect on the surface soil properties.(2)There are obvious differences in soil properties between different soil types in the study area,which is mainly caused by the different,namely,loess and Pisha sandstone soil,the difference in particle composition between the two soil matrix types bring about a large difference in soil properties.The thickness of the soil-covered increase gradually from the north to the south in the transition area from exposed Pisha sandstone to the soil-covered Pisha sandstone.During the transition to the south,the range of loess expands,the range of Pisha sandstone shrinks,sand content and phosphorus level decrease,and the soil clay,silt,moisture,organic matter,total nitrogen,available nitrogen content and enzyme activity increased gradually.At the profile level,the soil conditions above and below the loess-Pisha sandstone interface are also significantly different,indicating that the soil quality of loess is better than that of Pisha sandstone,the nutrient loss of Pisha sandstone soil is serious and the capacity of retaining fertilizer is low.(3)The evaluation results of MDS and weighted TOPSIS show that the comprehensive index of soil quality between artificially restored vegetation and natural restored grassland is as follows: Pinus tabulaeformis > Hippophae rhamnoides > Amygdalus davidiana > Natural grassland > Armeniaca sibirica.Pinus tabulaeformis and sea buckthorn obtained higher comprehensive evaluation scores of soil quality due to their better soil physical,chemical and enzymatic activity levels.The distribution of regional soil quality index is also consistent with water and organic matter.The soil quality in the loess region was higher than that of Pisha sandstone.Vertically,the surface soil quality index is higher.In the transition area from exposed Pisha sandstone to soil-covered Pisha sandstone,the implementation of vegetation restoration has improved the soil quality of the study area in varying degrees,among which the improvement effect of Pinus tabulaeformis and Hippophae rhamnoides is the best.However,the vegetation restoration has no significant effect on the improvement of phosphorus in the study area.Due to the particularity of the soil structure of Pisha sandstone,the water and fertilizer retention capacity of Pisha sandstone soil is extremely low,and the soil quality of loess layer is better than that of Pisha sandstone soil.Therefore,in the ecological environment management of the Pisha sandstone area,Pinus tabulaeformis and Hippophae rhamnoides can be selected for artificial restoration of vegetation,and appropriate amount of exogenous phosphate fertilizer can be added during the planting process to improve the level of soil phosphorus.On the other hand,the water and fertilizer retaining ability of soil-covered layer also plays a certain role in improving soil quality of Pisha sandstone.