Abstract
Pisha sandstone mainly distributes in the interprovincial border areas of Shanxi, Shaanxi and Inner Mongolia in the Yellow River Basin of China. These distribution areas are difficult to carry out effective treatment due to serious soil erosion and deteriorative ecological environment. Therefore, the main challenge is to improve the soil matrix of Pisha sandstone suitable for plant growth, which can be applied to soil ecological restoration and vegetation restoration in Pisha sandstone areas. In this study, the plant growth-promoting bacteria Bacillus halotolerans P75, Sinorhizobium meliloti D10, Bacillus megaterium H3 and Bacillus subtilis HB01 were used as raw materials to meet the challenge. After the strains were activated and centrifuged, the bacterial cell pellets were re-suspended in sterile water to obtain the four bacterial suspension of P75, D10, H3 and HB01. Then, the bacterial suspension was thoroughly mixed with organic/inorganic substrates at a volume-mass ratio of 1:1, and dried at 37 ℃ to prepare four kinds of single solid bacterial agents. Afterwards, 11 kinds of composite solid bacterial agents were obtained by mixing the four kinds of single solid bacterial agents uniformly according to different combinations of equal mass. The greenhouse pot experiment was carried out from March to April, 2019. 17 test groups in total were set in each pot with 300 g Pisha sandstone, where 15 test groups were the soil matrix of Pisha sandstone containing 15 different microbial agents at a mass ratio of 5% respectively, and two groups were the Pisha sandstone with the same amount of biological substrate and the Pisha sandstone without treatment. Each pot of soil matrix was watered regularly, and the soil indexes for the soil matrix of Pisha sandstone in each test group were tested after one month. A 20-day seedling experiment was performed on the planted alfalfa under the condition of the original potted soil matrix. The improvement effects of different solid microbial agents on the properties of Pisha sandstone were evaluated by the soil pH, organic matter content, available nitrogen content, available phosphorus content, available potassium content, enzyme activities and the number of bacteria, as well the seedling growth. The results showed that the addition of organic/inorganic substrates can improve the soil quality of Pisha sandstone, and promote the growth of plant seedlings, compared with the untreated control group. Compared with the effect of organic/inorganic substrates on improving Pisha sandstone soil, the addition of microbial agents can significantly increase the content of organic matters by 18.4%-30.0%, the content of alkali-hydrolyzed nitrogen by 19.7%-30.4%, the content of available phosphorus by 12.4%-47.8%, the content of available potassium by 25.3%-82.9%, the invertase activity by 13.2%-58.0%, the urease activity by 13.0%-37.7%, and the total number of soil bacteria reached more than 107 CFU/g. Compared with the effect of soil matrix containing biological substrate on Alfalfa seedling promoting, the soil matrix containing microbial agents can further increase the seedling height by 18.0%-39.2%, the root length by 37.4%-70.5%, the shoot fresh weight by 56.3%-94.1%, the root fresh weight by 106.5%-234.6%, the shoot dry weight by 32.8%-90.5%, and the root dry weight by 108.8%-301.2%. The optimum results were found in the compound agent A3 containing strains P75, D10 and H3, and A4 containing strains P75, D10, H3 and HB01. According to the soil indexes of each test group and the growth of Alfalfa seedlings, the optimal combination of P75+D10+H3 and P75+D10+H3+HB01 were finally determined for the improvement of the Pisha sandstone soil.
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