Soil Profile Reconstruction In Reclaiming Subsided Land With Yellow River Sediment

A large area of prime farmland is distributed in eastern China with high water table and flat terrain,and underground coal mines in this area usually has multi-layered superposed distribution of coal seams with large thickness.The overlapped areas of crop and mineral production are huge in eastern China.Coal mining caused a large area of farmland was destroyed,degraded and waterlogged,which resulted in increased difficulties of reclamation,huge agricultural economic losses,a large number of village relocation and increased social instability factors,as a result,there are a series of constraints in local area urbanization layout and ecological environment was deterioration in eastern China.Therefore,the prime aim of subsided land reclamation in this area is to improve the percentage of cultivated land,and filling reclamation technology is an effective method to achieve this purpose.At present,the traditional filling reclamation materials are coal waste and fly ash,but they application are limited due to shortage and risk of secondary pollution.The Yellow River is one of rivers with the highest sediment concentration among the word,and primary tasks of development and protection of the Yellow River are providing flood control capacity,more ways to utilize sediment and reduce sediment accumulation.Accordingly,Yellow River sediment can be used as filling material of subsided land along the Yellow River,and it is a kind of sufficient and safe filling reclamation materials.Filling reclamation with Yellow River sediment can improve the percentage of cultivated land in subsided land reclamation,and play a certain role in dredging of the Yellow River.However,filling reclamation with Yellow River sediment is a complex project,including many steps such as taking and transporting sediment,filling,draining,reconstructing soil and so on.Soil reconstruction is the core content of land reclamation in subsided land reclamation,and soil profile reconstruction is the most elementary part of soil reconstruction.Therefore,soil profile reconstruction is the most critical part of the technology of reclamation subsided land with Yellow River sediment,which directly determines the success or failure of this technology.Currently,there was no report on research of soil profile reconstruction in filling reclamation subsided land with Yellow River sediment,and present technology mostly originated from the traditional filling reclamation such as coal waste and fly ash.Therefore,there were some problems in present technology of filling reclamation subsided land with Yellow River sediment,such as insufficient thickness of soil cover on sediment,poor water and fertilizer holding capacity,more irrigation water during crop growth,poor crop growth and low yield,and so on.Consequently,it is necessary to research on soil profile reconstruction in filling reclamation subsided land with Yellow River sediment to improve soil physical and chemical properties and productivity of reclaimed land.This dissertation did some research on soil profile reconstruction in filling reclamation of subsided land with Yellow River sediment,based on the existing experiences of filling reclamation subsided land with Yellow River sediment and used related knowledge of pedology and agronomy.Firstly,A greenhouse experiment was conducted to investigate performance of columns containing soil-sediment profiles with different thickness of soil cover on sediment,which caused by one-time filling Yellow River sediment,which regarded as traditional filled soil profile.The optimal thickness of soil cover on Yellow River sediment was selected by measuring growth and biomass of maize plants,and analyzing the physical and chemical properties of soil and sediment,and this thickness of soil should to ensure crop growth and economic feasibility.Secondly,a greenhouse experiment was conducted to investigate performance of columns containing varying layers of soil and Yellow River sediment as proxies designing for reclamation strategies.The feasible multilayered soil-sediment profile was determined by measuring growth and biomass of maize plants,and analyzing the physical and chemical properties of soil and sediment,in order to innovate traditional soil profile of filling reclamation and improve soil productivity.Furthermore,field plot experiments were carried out to test and verify the results obtained by two greenhouse experiments,in order to get suitable soil-sediment profile with optimal thickness of soil cover on sediment and suitable multilayered soil-sediment profile with high soil quality and productivity.Finally,technical process of reconstruction of soil-sediment profile and multilayered soil-sediment profile in reclaiming subsided land with Yellow River sediment was discussed and summarized,in order to provide foundation and guideline of soil profile reconstruction in filling reclamation with Yellow River sediment.The results were as the following,(1)The optimal thickness of soil cover on Yellow River sediment in soil-sediment profile reconstruction,which caused by one-time filling sediment and regarded as a kind of traditional soil profiles,was researched by a greenhouse experiment.With increasing thickness of soil cover on sediment,maize growth was increased,when soil was 20-80 cm,dry biomass of shoot system of maize plant was lower 21.62%,13.19%,11.11%,3.70%,3.08% than CK,respectively,and dry biomass of shoot system of maize plant in CK was 50.21 g;when soil was 20-70 cm,dry biomass of root system of maize plant was lower 38.85%,37.71%,19.04%,8.38% than 80 cm,respectively,and dry biomass of root system of maize plant in 80 cm was 10.24 g.With increasing thickness of soil cover on sediment,total nitrogen,total phosphorus,total potassium of maize leaf was increased.The soil-sediment profile with thick thickness of soil was propitious to control pH and unpropitious for control electrical conductivity,furthermore,it was propitious to promote water and fertilizer holding capacity of whole profile,and water content,available nitrogen and available potassium content of soil were higher than CK due to water and available nutrients(available nitrogen,available phosphorus,available potassium)accumulated in the soil above Yellow River sediment,but organic matter content was lower than CK.When soil was 70,80 cm,maize growth(plant height,stem diameter,leaf area and chlorophyll),dry biomass,leaf nutrients(total nitrogen,total phosphorus,total potassium),water content and available nutrients(available nitrogen,available phosphorus,available potassium)of topsoil was similar to CK.In summary,with increasing thickness of soil cover on sediment,maize growth and water and fertilizer holding capacity of whole profile were increased,however,when the soil layer reached a certain thickness(70 cm),the influence of soil thickness was gradually weakened.Into consideration of soil requirement and construction cost,70 cm(topsoil is 30 cm)is the optimal thickness of soil cover on Yellow River sediment,and this thickness of soil can ensure crop growth and economic feasibility.(2)Multilayered soil-sediment profile reconstruction was researched by a greenhouse experiment,which caused by multi-times filling sediment in reclaiming subsided land with Yellow River sediment.Multilayered soil-sediment profile was favorable for maize seed germination,maize plant growth and root growth.Dry biomass of shoot system of maize plant in T8 and T11 was higher 22.60%,15.50% than CK2,and dry biomass of root system of maize plant in T8,T10 and T11 was higher 36.64%,29.78%,29.96% than CK1,and was higher 30.34%,23.8%,23.98% than CK2.Multilayered soil-sediment profile was favorable for holding water,available nutrients(available nitrogen,available phosphorus,available potassium),organic matter of topsoil,but it had no influence on pH,and it was unfavorable for control electrical conductivity.Multilayered soil-sediment profile was favorable for holding total nitrogen,total phosphorus of whole profile,but total potassium content is low and unfavorable for holding organic matter of subsoil among sediment.Multilayered soil-sediment profile was propitious to holding available nitrogen,available phosphorus,available potassium of upper and middle position of profile and holding available phosphorus,available potassium of lower position of profile.In addition,with increasing of total thickness of subsoil among different multilayered soil-sediment profiles,the growth,dry biomass(plant height,stem diameter,leaf area and chlorophyll),leaf nutrients(total nitrogen,total phosphorus,total potassium)were roughly increased,but multilayered soil-sediment profiles was weaken this trend,such as T6 and T7 with 30 cm total thickness of subsoil,T9 with 40 cm total thickness of subsoil,and CK2 had similar dry biomass and growth of maize,T7,T8-T11 with 40 cm total thickness of subsoil and CK1,CK2 had similar leaf nutrients(total nitrogen,total phosphorus,total potassium)contents.In summary,T8,T10 and T11 were good multilayered soil-sediment profiles had similar dry biomass and growth of maize,leaf nutrients(total nitrogen,total phosphorus,total potassium)contents to CK2.Therefore,the first layer of soil cover must have sufficient thickness to ensure the growth of primary roots of crops,and 50 cm is better than 40 cm.When the profile has two soil layers among sediment,the thicker one should be in a shallow position.However,in the deep position,two 10 cm soil layers among sediment layers were better than only one 20 cm soil layer.There are two soil layers among sediment were better than only one soil layers.(3)Soil-sediment profile reconstruction and multilayered soil-sediment profile reconstruction of filling reclamation with Yellow River sediment were studied by field plot experiment to test and verify the results obtained by two greenhouse experiments.In field,the optimal thickness of soil cover on sediment of soil-sediment profile was 70 cm,and the suitable multilayered soil-sediment profile was that with two soil layers among sediment,and the thickness of first layer of soil cover was 50 cm better than 40 cm.When the profile has two soil layers among sediment,the thicker one should be in a shallow position.However,in the deep position,two 10 cm soil layers among sediment layers were better than only one 20 cm soil layer.In the technology of filling reclamation of subsided land with Yellow River sediment,the multilayered soil-sediment profile reconstruction was one of efficient ways to get soil high quality and productivity.(4)Soil profile reconstruction technology of filling reclamation of subsided land with Yellow River sediment was discussed and summarized,and it was divided into soil-sediment profile reconstruction technology and multilayered soil-sediment profile reconstruction technology.The technical process of one-time and multi-times filling reclamation technologies with Yellow River sediment were discussed,then according to whether dividing strips of filling area or not,the technologies subdivided into 4 categories,1)undivided strips,one-time,one-layered filling reclamation of subsided land with Yellow River sediment,2)divided strips,one-time,one-layered filling reclamation of subsided land with Yellow River sediment,3)undivided strips,multi-times,multi-layered filling reclamation of subsided land with Yellow River sediment,4)divided strips,multi-times,multi-layered filling reclamation of subsided land with Yellow River sediment.And the follow charts,diagrams and specific implementation steps of every technologies were given to provide foundation and guideline of soil profile reconstruction in filling reclamation with Yellow River sediment.This dissertation did some research on soil profile reconstruction in filling reclamation of subsided land with Yellow River sediment,but did not do research on mechanism of water and solute transport in whole profile.In the further study,it is necessary to study regularities of water and solute transport and reveal its mechanism,promoting the renovation of filling reclamation technology.The technical process of one-time and multi-times filling reclamation technologies with Yellow River sediment were discussed in this dissertation,but still relatively simple,in further study,connecting and coupling mechanism of technical process of multi-filling and multi-backfilling soil should be studied to improve and perfect the method titled “Dividing strips of subsided land and multi-alternating filling these strips” of reconstruction of multilayered soil-sediment profile in filling reclamation of subsided land with Yellow River sediment.