| Coal resources are subject energy sources in China.There is no doubt that China is kept in the rapid development period of economy,so it has the huge demands for coal resources and this won't be changed in a short time.Relative to underground coal mining,opencast coal mining has high coalmining efficiency,high percentage recovery and low costs.The opencast coal mining proportion in China has been increased to 15% from 4%.Chinese opencast coal mines are mainly distributed in the western region which has the fragile ecological environment.As the important energy base in China,this region has the existing conditions of shallow burying,thick coal bed and thin basement and owns the large-scale intensive conditions for modern development.With the strategic western moving of mining industry,the western region has already become the main battlefield for Chinese energy development.Opencast coal mining needs to strip all surface soil and stratum above the ore bed,so it inevitably will cause the most direct influences on the land and ecological environment.The western region is located in the typical zone of wind erosion and water erosion and belongs to the eco-fragile region of arid and semiarid.Since the ecological threshold is low and anti-disturbance rejection is poor,intensive construction and high-strength exploitation of coal base make this region present in the strong disturbed tendency,so as to greatly affect the sustainable development of regional ecological environment.As a result,it is urgent to realize land rehabilitation and ecological reconstruction in the western opencast mining areas.The western mines are featured with arid,less rainfall,poor soil structure and low nutrition,resulting in extremely difficult ecological remediation in the land.At present,land rehabilitation in the land applies the engineering reclamation of backfilling gangue in the bottom and overlying ground.However,the waste dump after earthing has no soil mass structure and has the poor moisture,fertilizer retention,and fewer nutrition contents,so it is difficult for plants' survival and growth.Hence,the key for ecological remediation in this region is to improve existing soil,improve soil nutrition contents and increase moisture and fertilizer retention.On the basis of learning from existing result experience,by taking full advantage of relevant knowledge in edaphology and agronomy and starting from fully utilizing local raw materials,five raw materials of aeolian sandy soil,red clay,gangue,maize straw and humic acid were recombined into sponge-nutrient soil of 27 formulas with different proportions.In the greenhouse experiment,Alfalfa was used as the host plant to compare and analyze plant growth trait of sponge-nutrient soil of 27 formulas and select the optimal formula of sponge-nutrient soil.Meanwhile,from different aspects of soil physical properties,nutrient contents and biological properties,the response of spongenutrient soil with different formulas was analyzed and compared.Meanwhile,the mechanism of promoting plant growth for the sponge-nutrient soil with the optimal formula was discussed.On the basis of selecting the optimal formula for the spongenutrient soil,the local application method of interbedding the sponge-nutrient soil layer in the aeolian sandy soil was proposed.Based on the greenhouse experiment,compared and analyzed the influences of different layers and interlayer thickness in sponge-nutrient soil on plant growth features and nutrient effect of soil profile.Meanwhile,indoor column experiment was used to simulate the infiltration and evaporation process of soil profile configuration in different types of sponge-nutrient soil and study the influences of sponge-nutrient soil's interlayer position and interlayer thickness on soil profile moisture operation,distribution law and retention performance,as well as water retention capacity.The main results including:(1)The optimal formula of sponge-nutrient soil that is suitable for the growth of Alfalfa was selected.By considering the facilitation of 27 kinds of sponge-nutrient soil on growth status of Alfalfa,it showed that 1:2 compound of aeolian sandy soil and red clay added with 15% of gangue,5% of maize straw and 0.05% of humic acid was the optimal formula of sponge-nutrient soil,which significantly promoted growth of Alfalfa.Plant height,root system length,root diameter,root surface area,aboveground biomass,underground biomass,aboveground total nitrogen,total phosphorus and total potassium in Alfalfa under the optimal formula of sponge-nutrient soil improved by 223.28%,131.80%,239.20%,650.45%,624.76%,1298.36%,78.47%,324.14%,and 82.05%,respectively by comparing with aeolian sandy soil.This formula of sponge-nutrient soil fully realized the resource utilization of aeolian sandy soil,gangue and maize straw,while promoting plant growth.It would alleviate workload and reduce ecological remediation costs.(2)The mechanism of using the optimal formula of sponge-nutrient soil to promote growth of Alfalfa was revealed.Its mechanism of promoting plant growth included formation of the good soil texture,improvement of moisture physical properties,improvement of organic matters and nutrient contents,biological activity and the role of excretion on soil.First of all,the optimal formula of sponge-nutrient soil significantly improved the soil physical properties.The soil texture in aeolian sandy soil was sandy soil.The adding of red clay effectively regulated the soil grain composition,thus soil texture became sandy loam from sandy soil.Relative to aeolian sandy soil,total porosity,capillary porosity,saturation moisture content,capillary moisture capacity,field capacity and >0.25 mm water stable aggregate content in the optimal formula of sponge-nutrient soil respectively improved by 30.45%,97.72%,91.60%,144.58%,147.41%,and 181.03%.The volume weight was reduced by 19.75%.In addition,the optimal formula of sponge-nutrient soil significantly improved soil nutrition content.Before improving aeolian sandy soil,in addition to rapidly available potassium,other nutrient contents were kept in the low level.Total nitrogen,organic matters,available nitrogen,rapid available phosphorus and rapidly available potassium in the optimal formula of sponge-nutrient soil significantly increased by 3373.33%,1141.48%,269.97%,1974.60% and 620.45% by comparing with the aeolian sandy soil.The PH value decreased by 8.31%.Furthermore,the optimal formula of sponge-nutrient soil significantly increased the number of microbial population.Relative to aeolian sandy soil,bacteria,fungus and actinomyces in the optimal formula of the sponge-nutrient soil significantly increased by 1056.52%,1854.55% and 1172.50%,respectively,relative to aeolian sandy soil.The total microorganisms increased by 1075.29%.(3)By aiming at the application method of sponge-nutrient soil,the local application method of interbedding sponge-nutrient soil layer in aeolian sandy soil was proposed.The suitable interlayer position and interlayer thickness of sponge-nutrient soil was selected.Firstly,the sponge-nutrient soil layer in the aeolian sandy soil effectively promoted growth of Alfalfa.The facilitation was different for different interlayer position and interlayer thickness in sponge-nutrient soil.Aboveground biomass and underground biomass in Alfalfa under the soil profile with the interlayer position of 10 cm and interlayer thickness of 15 cm was the optimal and improved by 116.39% and 146.82% by comparing with the sandy soil column CK.The interlayer position and interlayer thickness were the most suitable application method of sponge-nutrient soil.When interlayer thickness of sponge-nutrient soil was the same,the facilitation in 10 cm of interlayer position on plants was greater than 5cm and 15 cm.When the interlayer position was the same,the interlayer thickness increase of sponge-nutrient soil was good for promoting growth of Alfalfa.When the interlayer thickness was15 cm,the facilitation was the most obvious.Secondly,sponge-nutrient soil had the improvement and accumulation role on entire nutrient of soil profile(pH,organic matters,total nitrogen,available nitrogen,rapidly available phosphorus and rapidly available potassium).The interlayer thickness increase of spongenutrient soil was beneficial to improve the entire nutrient content of profile.Soil profit nutrient content with interlayer thickness as 15 cm was better than 5cm and 10 cm of interlayer thickness.Nutrient content of sandy soil column CK was present in the reducing tendency with the depth increase.The nutrient content in different depth was lower than the layer soil profit in the corresponding depth.For different types of layer soil profit,influences of interlayer position and interlayer thickness on soil nutrient contents were not significant.The nutrient contents in soil profile of each layer didn't have significant difference.For the soil profile in the same layer,nutrient contents in the interlayer were obviously higher than the upper layer and bottom layer.There was no significant difference in nutrient contents between the upper layer and bottom layer,but the nutrient contents in the bottom layer were higher than the upper layer as a whole,indicating that the interlayer of sponge-nutrient soil improved nutrient contents in the lower aeolian sandy soil.In the long term,the dielectric layer that is suitable for the plant growth in the entire soil profit was present in the crescent tendency.(4)Interlayer position and interlayer thickness of sponge-nutrient soil had the significant influences on infiltration performance of soil profile.The interlayer of spongenutrient soil reduced the infiltration performance of soil profile.Soil profile had the lowest infiltration performance in sponge-nutrient soil in 10 cm of interlayer position and 15 cm of interlayer thickness.When the interlayer thickness was the same,while interlayer position was 5cm,10 cm and 15 cm from the soil surface,as interlayer position closing to the soil surface,wetting front spent the shorter time arriving the upper interface of the interlayer,thus the corresponding accumulative infiltration capacity was small.The 10 cm of interlayer position from soil surface had the maximum inhibition on moisture moving.When interlayer position was the same and interlayer thickness was 5cm,10 cm and 15 cm,the thicker interlayer thickness was,the larger inhibition on moisture moving would be.The linear function could be used to describe the relation between advance distance and advance time of wetting front for different soil profiles.Kostiakov could greatly fit for the infiltration process of different soil profiles.(5)Interlayer position and interlayer thickness of sponge-nutrient soil had the significant influences on evaporation features of soil profiles.The interlayer of spongenutrient soil reduced the cumulative evaporation of soil profile.Soil profile had the lowest cumulative infiltration in sponge-nutrient soil in 5cm of interlayer position and 15 cm of interlayer thickness.When the interlayer thickness was the same and interlayer position was distant from soil surface for 5cm,10 cm and 15 cm,as interlayer positioning closing to soil surface,the inhibition on evaporation would be stronger.When the interlayer position was the same and interlayer thickness was 5cm,10 cm and 15 cm,the thicker interlayer thickness was,the stronger inhibition on evaporation would be.The secondary model greatly simulated the relation between accumulated evaporation capacity and time for each soil profile.After drainage for 48 hours and evaporation for 30 days,waterholding capacity under T6 treatment was the highest,reaching 129.10 mm and 76.35 mm,respectively.This indicated that water holding capacity of soil profile for sponge-nutrient soil with 10 cm of depth and 15 cm of thickness under the aeolian sandy soil was the optimal to realize the water retention effect. |
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