Effect and influence of soil improvement in waste dumps under different organic composite substrate experiments

Open-pit coal mining leads to the destruction of land and the ecological environment, exacerbating the contradiction between people and land. Reclamation of waste dumps can improve land utilization and promote the healthy development of land use. The study takes the Hequ open-pit coal mine as the research object, exploring the effect and influence of different organic composite substrates on soil improvement in the open-pit coal mine waste dumps. The influence of different composite matrix ratios on the soil improvement effect of open-pit coal mine waste dumps, the study takes the Hequ open-pit coal mine as the research object. 15 sets of pot experiments were set up based on different proportions of organic chicken fertilizer, corn straw, and soil content to conduct alfalfa planting experiments. The effectiveness of soil improvement was reflected by changes in indicators such as germination rate, plant height, leaf length, and soil physicochemical properties. The results indicated that: There were significant differences in plant germination rate and plant height among different organic composite substrate schemes, but there were no significant differences in leaf number and leaf length among different schemes. However, there was no significant difference in the number and length of leaves. The N₁₀ group (70% soil +20% organic fertilizer +10% corn straw) had the best effect on improving soil fertility, significantly promoting the growth of alfalfa, with the highest degree of promotion in plant germination rate and height. It could also maintain the pH within the optimal range of for a long time. When the organic fertilizer content was greater than or equal to 30%, it would have an inhibitory effect, causing soil acidification and affecting seed activity. Through statistical analysis, it was found that the organic matter and alkaline nitrogen content showed an overall trend of first decreasing and then increasing over time, while the overall trend of available phosphorus content continued to decline. The N₁₀ group ultimately increased the organic matter content, alkaline nitrogen content, and available potassium content by 43.10%, 71.52%, and 9.17%. It effectively increased soil nutrients and greatly improved soil fertility. With time, When the proportion of organic fertilizer applied was constant, the increase in straw significantly increased the organic matter content in the soil. The on-site experiment found that the N₁₀ group had little effect on the number of maize leaves. Still, after treatment, the overall plant height of maize could reach 1.34 times that before treatment, and the seed survival rate increased by 60%. The SPAD value increased by 40.62%, and the chlorophyll content significantly increased compared to untreated corn. Compared with the application of a single organic fertilizer, the combined application of organic fertilizer and straw was more effective in maintaining soil fertility, increasing soil organic matter content, and slowing down soil alkalization in the long term. The study has proposed the effective measures to improve the soil quality of the Hequ open-pit coal mine's waste dumps, to provide theoretical and practical basis for the ecological restoration of similar the open-pit coal mine waste dumps in the Yellow River Basin.