| Along with the rapid development of China's economy,a large number of infrastructures such as railways and highways have increased the environmental and ecological pressures while facilitating people's lives.In particular,the deep excavation and high filling in the construction process produces a large amount of spoil ground slag.While occupying a large amount of land resources,due to its disorderly stacking and excessive disturbance,in addition to generating safety hazards,it is also due to extremely low productivity to form an abandoned land that cannot be used.In order to restore the land productivity of these disturbed soils as quickly as possible,and alleviate the pressure on the environment and cultivated land,this paper takes the reconstituted soil test plots that have been implemented for 5 years of vegetation restoration as the research object,using the combination of longitudinal(time)and horizontal(single and mixed)comparisons,the principal component analysis method was used to comprehensively evaluate the effect of each recovery model on the fertility improvement of the reconstructed soil,and the following main conclusions were drawn:(1)Under the experimental conditions,the physical properties of the reconstructed soil1 showed that the soil water content increased in the single-mode and mixed-seeding mode during the past five years,but the soil water content in the vegetation planting plot was lower than that in the blank control plot due to the transpiration of the above-ground part of the plant.During the past five years,the total porosity of the single-seeding mode remained stable,and the total porosity of the mixed-seeding mode increased significantly.The capillary porosity and field water holding capacity of the single-seeding and mixed-seeding mode increased slightly,and the total porosity,capillary porosity and field water holding capacity of the soil were larger than those of the blank control plot due to vegetation restoration.The improvement effect was as follows: mixed-seeding mode > single-seeding mode.The soil bulk density is between 1.12g/cm3-1.37/cm3.The five-year vegetation restoration reduces the soil bulk density of the single-seeding mode slightly,while the mixed-seeding mode reduces the soil bulk density obviously.Caragana + Sweet clover mode has the best effect on reducing the soil bulk density.The number of soil aggregates in >0.25 mm range from 41% to 57%.CKK + LPL has the best effect on the formation and stability of soil aggregates.The chemical properties were as follows: during the five-year vegetation restoration period,the contents of available potassium,total nitrogen and organic matter increased from 2014 to 2018,103.5-167.425mg/kg changed to 134.5-270.6mg/kg(available potassium),0.188-0.235g/kg became 0.288-0.487g/kg(total nitrogen),5.5-6.7g/kg became7.0-11.8g/kg(organic matter).However,the available phosphorus content fluctuated and decreased from 3.9-9.1 mg/kg in 2014 to 1.9-7.5 mg/kg in 2018.The improvement effect of soil physical and chemical indicators of soil 1 is weakened with the increase of soil depth.By measuring and analyzing the plant height,coverage,biomass,root-shoot ratio and dry-to-sale ratio of the restored vegetation on soil 1,the growth of vegetation on the reconstructed soil is realized: the mixed mode is better than the unicast mode,the growth condition of AFL+LPL was the best.(2)Under the experimental conditions,the physical properties of reconstructed soil 2showed that soil water content increased significantly in the early stage of vegetation restoration in five years.With the increase of restoration time,soil water content of single-seeding mode increased significantly,while that of mixed-seeding mode increased slightly.In the past five years,the total soil porosity and field water holding capacity of single and mixed sowing patterns increased significantly,and the increase of mixed sowing patterns was larger than that of single sowing patterns,while the capillary porosity increased slightly.Soil bulk density ranged from 1.19 g/cm3 to 1.31/cm3,reaching the average soil bulk density range of the Loess Plateau.The soil bulk density of the unisown and mixed sowing plots decreased significantly and were smaller than that of the blank control plots after five years of vegetation restoration.The decrease of mixed sowing mode was greater than that of unisowing mode,and the decrease of soil bulk density of CKK +LPL was the most obvious.The number of soil aggregates in >0.25 mm range from 39.03% to 55.31%.The stability of soil aggregates in mixed sowing mode is mostly stronger than that in single sowing plot.The mixed sowing mode of MSL + LPL has the best effect on improving soil aggregates and stability.The chemical characteristics showed that after five years of vegetation restoration,the contents of available potassium,total nitrogen and organic matter increased from 2014 to 2018,122.5-142.7mg/kg changed to 166.6-349.1mg/kg(available potassium),0.19-0.26g/kg changed to 0.38-0.56g/kg(total nitrogen),3.0-7.7g/kg became8.8-10.2g/kg(organic matter),but the available phosphorus content decreased from13.8-16.6mg/kg in 2014 to 8.7-10.7mg/kg in 2018.The improvement effect of soil physical and chemical indicators of soil 2 is weakened with the increase of soil depth.By measuring and analyzing the plant height,coverage,biomass,root-shoot ratio and dry-to-sale ratio of the restored vegetation on soil 2,the growth of vegetation on the reconstructed soil is realized: the mixed mode is better than the unicast mode,the growth condition of AFL+LPL was the best.(3)The correlation analysis between soil quality factors and vegetation productivity under different planting patterns of soils 1 and 2 shows that:There was a significant negative correlation between the dry ratio of vegetation and soil water content,and a significant positive correlation with capillary porosity,aggregate size and organic matter content.Root-shoot ratio was significantly negatively correlated with capillary porosity,available phosphorus,and available potassium.Soil bulk density was significantly negatively correlated with capillary porosity,field water holding capacity,total nitrogen and organic matter content,and soil organic matter content was significantly positively correlated with soil aggregate size and total nitrogen.Soil capillary pores are more conducive to the storage of soil moisture and organic matter.Soil aggregates are conducive to the accumulation of soil nutrients.Restoration of vegetation growth and development affects the physical and chemical properties of the reconstructed soil,thus affecting the fertility of the reconstructed soil.(4)The 11 physical and chemical indexes selected in this experiment were standardized,and the comprehensive scores of reconstructed soil quality were calculated and ranked by principal component analysis according to the weight of each index.The results showed that the quality of reconstructed soil 1 was as follows:the improved effect of mixed planting CKK+MSL is the best,the improved effect of unicast MSL is the best.The quality ofreconstructed soil 2 was as follows: the improved effect of mixed planting AFL+LPL is the best,the improved effect of unicast MSL is the best.The overall improvement effect of the two reconstructed soils is as follows: mixed mode > unicast mode,legume and gramineous plant mixed mode > legume and legume mixed mode. |
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