Research And Application Of Improved Materials For Raw Soil Rapid Maturation

Raw soil is often applied as carrying soil for reclamation of mine waste dumps and restoration of contaminated sites.The so-called raw soil refers to the original soil that has not been artificially disturbed.Due to its unmatured with poor physical structure,lack of chemical nutrients and low microbial activity,it is difficult for plants to grow.Soil maturation refers to the process of making gradual transformation of natural soil（raw soil）into fertile farming soil（mature soil or oily soil）which is suitable for crop growth.However,the natural maturation of soil always needs decades of years.So rapid soil maturation has become an important research on topic of soil improvement.In this study,humic acid（HA）,super absorbent polymer（SAP）and biochar（BC）were used as raw soil improvement materials.using single-factor and composite orthogonal test designs.Through soil simulation cultivation,potted and field application experiments,it was used to study the effects of improved materials on the physical structure,chemical nutrients and microbial activity of the raw soil during the raw soil maturation.It was revealed the mechanism of raw soil maturation.And it was developed and applied the composite materials for rapid maturation of raw soil.The main results of the research are as follows:（1）It revealed the difference of the physical and chemical properties of different materials on the maturation of raw soil and proposed the optimal combination of composite materials for soil maturation.Under nature,the treatment of pure raw soil has not been matured.Humic acid,super absorbent polymer and biochar were used to simulate the maturation of raw soil,respectively.（1）It showed without adding improvement materials,raw soil cannot be matured for a short period of time under nature.The chemical properties of semi-raw soil（1:1 mature soil:raw soil）were not significantly changed,and the physical properties were improved slowly.The content of water-stable large aggregates（>0.25mm）had increased significantly.Comprehensive analysis and calculations,semi-raw soil would take about 5 years to achieve the level of mature soil by organic fertilizers and chemical fertilizers.（2）In the treatment of semi-raw soil with three materials added separately,the physical structure of semi-raw soil could be improved,but it did not reach the level of mature soil.Inferred from linear changes,it taked about 3 years for the physical properties to reach the level of mature soil,and the chemical fertility of adding super absorbent polymer 3 g·kg^-1 could reach the medium fertility level in 126 days,but it still did not reach the level of mature soil.（3）In the semi-raw soil treatments with composite application of materials,the chemical properties of each treatment reached the level of mature soil in 126d,but the physical properties did not reach.（4）Under the condition of composite application of three materials and planting of plants,chemical properties of soil cultivated for 42 days to reach the level of mature soil,and the physical properties of the soil reached the level of mature soil between 84 and 126 days.It had shown that composite materials could improve the physical structure of the soil,increase the content of soil chemical nutrients,the activity and diversity of microorganisms,and promote plant growth.Orthogonal experiments of the three materials showed that the combined effect of composite materials on soil maturation and plant growth was in order:super absorbent polymer>humic acid>biochar.It was analyzed that the best ratio of the three composite materials is 3 g·kg^-1 super absorbent polymer:3 g·kg^-1 humic acid:10 g·kg^-1 biochar.（2）It revealed the mechanism of the maturation effect of different materials and their combinations on raw soil.（1）Through correlation analysis,it was proved that the physical properties such as bulk density,porosity and 0.25-5mm aggregates of semi-raw soil were closely related to chemical indicators such as available nitrogen,available phosphorus and organic matter.The above-mentioned physicochemical properties were most closely related to plant growth.Super absorbent polymer had the greatest impact on soil aggregates of 1-2mm,0.25-0.5mm,p H,available nitrogen,available phosphorus and organic matter.Humic acid had the greatest impact on soil bulk density,soil porosity,0.5-1mm soil aggregates,and total nitrogen.Biochar has the greatest impact on soil 2-5mm aggregates.（2）It could be obtained by factor analysis that a single material mainly adjusts the"chemical bond stability"and"physical bond stability"between compounds or between compounds and soil to improve the maturation process of the soil.And the physical effect of materials on the maturation of raw soil is greater than the chemical effect.Composite materials mainly regulated the"number of ring structures"formed in the soil,"stability of physical bonds"and"stability of chemical bonds"to influence the soil maturation process.In the application of composite materials with no plants,the chemical effect on the maturation of raw soil was greater than the physical effect.In the application of composite materials,the order was chemical effect>physical effect>microbial effect.（3）It revealed an appropriate ratio of raw loess as carry soil for fly ash fields and increasing corn yield and promoting soil improvement.Combined with a series of soil experiments,the optimized amount of raw loess was added to the fly ash field soil in Shexian County,Hebei.The addition of raw loess to the fly ash field could effectively improve the physicochemical properties and microbial activity of the fly ash field soil to achieve crop suitability.Adding the improved composite material of the above-mentioned soil amendment to the fly ash field soil,it showed the optimal combination of the soil was the addition of 20%raw loess and 900kg·mu^-1 composite material.Field experiments showed that after improved,the yield of corn increased by 94.54%compared with the control,and the economic income increased the most.At the same time,it could effectively improve the physical structure of the soil,increase chemical nutrients and microbial diversity.