| There are many environmental problems from coal mining and coal combustion, the arable land loss and regional ecological environment destruction for a large area surface subsidence, the environmental pollution of atmosphere, water and soil through dust and leachate from solid waste, and so on. Furthmore, a great quantities of lands are occupied by the coal-series concomitants (i.e. coal gangue) and coal combustion residues (i.e. fly ash). Some engineering measures in coal mining areas were applied in response to the challenge of these environmental problems to sustainable development, that were the land reclamation and ecological environment restoration by reconstructing soil profiles filled with the solid waste. One of the important rilling matrix was fly ash (FA). Water movement and solute transport mechanism of reconstruction soil profiles are the key problems which should be studied and solved if the land use pattern of the reclamation soil is woodland or farmland.Soil columns and field plots were built to focuse on simulating water infiltration and water balance under the crop growing conditions in reconstruction soils. The possibility is also studied of high soluble salt in FA layers transporting to deeper soil layer or groundwater environment, including salinity concentration variation of reconstruction soil profiles. On this basis, the response of crop growth to water-salt conditions change and fertility quality of the reconstruction soil were discussed to improve the soil water-salt movement theories and plant cultivation field managements of coal mining areas.(1) The soil columns of two different cover soil thickness (20cm and35cm) were designed for studying the water infiltration and salt migration of reconstruction layered soil, with controling two different groundwater levels (-115cm and-300cm). The results show that the differences exist but does not significantly of the experimental designed two topsoil thickness affecting on the infiltration front downshift rate and the moisture infiltration has obviously interface features between the cover soil and FA layer. At the same time, K+and Cl" of FA will rapidly move downward along with moisture under strong water supply. The short-term sharp rise of salt ion concentration is very easy in deeper soil layer or groundwater around if no proper pollution prevention measures. In addition, the groundwater table can remarkably affect on water infiltration of the reconstruction soil. The infiltration front is well-regulated down under the low groundwater table condition, while the interface cemented phenomenon appears between the infiltration front and capillary water rise surface under the high groundwater table condition, the surface confrontation-40cm and time12h after irrigation.(2) The field water balance of reconstruction soil under the extreme climate conditions were simulated by Hydraus-1D software according to precipitation and evaporation data from2001to2010in Huainan, China. The results show that reconstruction soil moisture contents are obvious influenced by the meteorological conditions when the groundwater level is low (-300cm), and the difference is about0.100cm3/cm3between dry years and wet years. Especially, moisture changes are significant in the cover soil. Moreover, the water content in FA layer is substantially independent of meteorological conditions under the high groundwater level (-115cm), always near saturated. And water content variable magnitude is also relatively small. While the topsoil moisture content fluctuates along to the field water content and can meet the demand for crop growth, whether drought or wet years. In this case, the effect difference is very small of the experimental two topsoil thickness to water content.(3) The water balance and salt distribution of reconstruction soil profiles with wheat growth were studied through establishing the experimental plots of cover soil25cm and45cm, setting the control plots and controlling the groundwater table (-150cm). The results show that the moisture content in FA layer of experimental plots is closed to the saturated water content in the whole wheat growth cycle and less subjected to weather conditions, while that of cover soil is the significant positive correlation to the rainfall. Furthermore, the topsoil water content of experimental plots is lower than those of the control plots in wheat growth periods and the limited cover soil thickness increase does not change the moisture conditions of reconstruction soil filled with FA. Even more, the Richards equation with root uptake has defect as describing field water content variation of reconstruction soil, namely the calculated values lower than measured ones. So the concept of compensation factor is put forward to Amending Richards equation, which is calculated as λ=γ*(dpb/d(?)). Meanwhile, SO42-, Mg2+, and Ca2+concentration of soil in experimental plots are higher than that in control plots, and the total soluble salt content also higher, while CO32-and HCO- concentration are lower. The thinner of topsoil, the poorer of the ability from accumulating and keeping soluble salt in whole wheat growth cycle. Besides, the distribution characteristics of soluble salt components is clear in reconstruction soil profiles. CO32-and HCO" concentration gradually decrease from the topsoil to FA layer, while those of Cl-, SO42-, and four cations gradually increase in relevant position in various stages of wheat growth.(4) The inconsistent phenomenon is obvious between water-salt conditions of reconstrucion soil filled with FA and wheat grain yield, that is, water content in FA layer of experimental plots is always higher than that of the control ones, but the wheat grain yield remarkably lower (p<0.05). Two reasons mainly are uncovered form research results. Although water content of FA layers is high nearly saturated one but the its impact on topsoil is less because of FA properties with low bulk density, large particles specific surface area, and strong water suction holding capacity firstly. Secondly, low salinity content and fertility quality in reconstruction soil affect on wheat growth and grain yield. Model dY/dH=(-0.3632+0.0021H)*H+11.315can be described the relation between topsoil thickness and wheat yield.(5) This paper built the fertility quality evaluation index system on the basis of studying soil physico-chemical properties. And the weight coefficients were assigned to each index with the method of principal component analysis and expert scoring combination to establishing the reconstruction soil fertility quality evaluation model. The assessment results that soil fertility composite index of the control plots is the highest, following cover soil45cm, and that of topsoil25cm in experimental plots is the minimum, which is consistent with the results of wheat grain yield on field plots. Additionally, the correlation coefficient is0.9784between nutrient fertility indexes NFI and fertility quality comprehensive index IFI of reconstruction soil, expressively remarkable correlation (p<0.01, n=12). |
PDF Full Text Request