| As one of the most valuable resources, soil is suffering from severe degradation Problems including land desertification, decrease in quantity and quality of arable land caused by soil depletion and pollution have attracted wide attention. In the aspect of soil repair and improvement, people have launched a large number of research projects however with little effect.The aim of this research was to use subsoil as the main substrate, and add vermicompost to adjust the properties of the subsoil, in order to make it more suitable for the growth of crops. Modified subsoil can be used as a repair material for polluted soil or directly as potting soil. Vermicompost was used as research material. vermicompost has good physio-chemical and biological characteristics, which are beneficial for soil improvement. Given the resources of subsoil are rich, to modify and use non-polluted but poor subsoil will become an important method in improving agricultural productivity, food production, horticultural practices, road planting, as well as the improvement of soil pollution.Using vermicompost to improve orchard subsoils, the research could be divided into three main parts:the incubation process, nutrient status after stabilization, and the effects on crop growth.Orchard subsoils were mixed with vermicompost at the percentages of 5%,10%,15%, 20% (by weight) respectively (T1, T2, T3 and T4), while control (CK) was prepared without adding vermicompost. The mixture was placed in a plastic box and cultivated for two months at room temperature. Samples were taken to determine water soluble substances, soil available nutrient and trace element of the mixture. After the mixture was stabilized, physical and chemical properties of the new soil were determined. The ability of phosphorus and lead adsorption was also evaluated. At the final stage, Chinese cabbage was planted in the above five new soils. After a week the cabbage biomass was determined and root system scanned and analyzed. Plant leaf chlorophyll content and the nutrient content were determined at the harvest after a month growth.The main results were as follows:(1) Adding vermicompost in subsoil could increase a variety of available nitrogen and phosphorus contents, and overall the fertility of soil, thus maintained a stable fertility. However, this might also lead to high concentration of electrolytes, which often increase crop osmotic stress degree and the load of high concentration of nitrogen and phosphorus pollution in aquatic environment.(2) Optimal vermicompost addition (5%～10%), not only kept the water-soluble nutrients and the total soil nutrient contents at a desirable level for crop growth, but also helped to reach a stabilization stage in a relatively short period of time. These treatments didn’t affect water soluble nitrogen and phosphorus contents, avoiding water pollution.(3) Addition of vermicompost into the ochard subsoils improved soil physical and chemical properties to a certain extent. Soil bulk density was reduced, while soil porosity water holding capacity, and air permeability were increased. These ensure full contact of roots and soil water, fertilizer, and oxygen. Optimal vermicompost addition (5%～10%), the range of soil bulk density is 1.08 g·cm-3 to 1.02 g·cm-3, which would eventually benefit crop roots’ growth.(4)With the increase of vermicompost content, adsorption of lead to soil increased significantly, the same happened to phosphorus. Although a large portion of phosphorus was fixed by subsoil-vermicompost mixture but the available phosphorus content in vermioompost was high enough to satisfy the crop growth.(5) Addition of vermicompost increased the leaf content of chlorophyll and content of carotenoids of Chinese cabbage, and therefore the photosynthetic capacity. Moreover, the uptake of major nutrients such as nitrogen, phosphorus and the growth of Chinese cabbage were improved. An optimal ratio of vermicompost (5%) significantly increased biomass and root growth of Chinese cabbage seedlings, such as root length, root surface area, root volume, the number of root tips were significantly increased compared to the control, and promoted the maximum absorption of beneficial nutrients. Relatively higher ratio of vermicompost addition lead to a significant increase of nitrate content from 22.6mg·g-1 to519.8mg·g-1,which causing imbalance of soil nutrients and the increase of conductivity. These together suppressed seed germination, inhibited the growth of seedling and roots of Chinese cabbage, thus prevented the seedling biomass from increasing.In conclusion, the optimal improving effects were achieved on orchard subsoils with the addition vermicompost at a ratio 5% by weight... |
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