Purpose Stabilization of weak soil can be achieved through different methods, some of which include jet column, cement stabilization and fly ash stabilization. Unfortunately, the use of the aforementioned methods of soil improvement affects the environment negatively thereby leading to environmental degradation. With the aforesaid impediment in mind, the need for devising methods of weak soil improvement becomes pertinent. Methods Bacillus sp. — a non-pathogenic organism found abundantly in soil — was investigated in this study as a potential agent of soil improvement. The usability of Bacillus sp. in soil improvement was investigated with direct shear tests and permeability tests under optimum conditions in this study. Result Time-dependent study on the effect of the ureolytic bacteria Bacillus sp.-induced calcium carbonate precipitation shows reduction in permeability and increase in the strength of the soil under study. On exhaustion of the available nutrients in the soil, however, the strength of the soil is not negatively impacted. Conclusion Microbially induced calcium precipitation by Bacillus sp. is effective in soil improvement as such it may serve as substitute for conventional soil stabilization techniques. The ability of the bacteria to precipitate calcium carbonate in the soil leads to reduction in the permeability and increase in the shear strength of the soil.

In this study, aimed to investigate the effect of bacterial fertilizer: A (Bacillus spp., Trichoderma spp. ), B (Azorhizobium, Azotobacter and Azospirillum) and C (Azotobacter spp., Bacillus spp. and Pseudomonas putida) on soil carbon mineralization. On the application of A, B and C bacterial fertilizers on the sterilized control soil, whose initial carbon mineralization rates is 1.1%, mineralization rates of 5.12%, 3.54%, and 10.78% were respectively recorded. According to these results, it was observed that the application of bacterial fertilizer increased the carbon mineralization rate of the sterilized control soil by 365.45%, 221.82% and 880%, respectively. A carbon mineralization rate of 7.03%, 6.15% and 12.95% was recorded in the non-sterilized soil sample whose initial carbon mineralization rate is 5.1%, thereby increasing the mineralization rate by 25.31%, 9.63% and 130.84%. The application of the bacterial fertilizer to the soil was found to increase the soil carbon mineralization rate. It is recommended to incorporate bacterial fertilizers with CO2- sequestering materials, such as biochar, to mitigate the fluctuations in the natural balance due to carbon release.

Purpose: Stabilization of weak soil can be achieved through different methods, some of which include: jet column, cement stabilization and fly ash stabilization. Unfortunately, the use of the aforementioned methods of soil improvement affects the environment negatively thereby leading to environmental degradation. With the aforesaid impediment in mind, the need for devising methods of weak soil improvement becomes pertinent. Methods: Bacillus sp. - a non-pathogenic organism found abundantly in soil - was investigated in this study as a potential agent of soil improvement. The usability of Bacillus sp. in soil improvement was investigated with direct shear tests and permeability tests under optimum conditions in this study.Result: Time-dependent study on the effect of the ureolytic bacteria Bacillus simplex induced calcium carbonate precipitation shows reduction in permeability and increase in the strength of the soil under study. On exhaustion of the available nutrients in the soil however, the strength of the soil is not negatively impacted.Conclusion: Microbially induced calcium precipitation by Bacillus sp. is effective in soil improvement as such it may serve as substitute for conventional soil stabilisation techniques. The ability of the bacteria to precipitate calcium carbonate in the soil leads to reduction in the permeability and increase in the shear strength of the soil.

This study is aimed at determining the characteristics and microbiota of soil upon which some Turkish Colchicum (Colchicaceae) species naturally grows. For this aim the rhizosphere soil samples of Colchicum balansae Planch., Colchicum triphyllum Kunze and Colchicum variegatum L. were analysed in this research. The carbon mineralization rate of C. balansae soil at p<0.05 is significantly different from that of the other two soils. In terms of nitrogen mineralization, significant difference exists between all the three soils (p<0.001). Colchicum variegatum rhizosphere was found to have the highest bacterial diversity. The results revealed that 254 bacterial species were common to the three rhizosphere soils, 35.60% of the bacterial species were unique to C. variegatum soil while 21.89% and 22.67% of the bacterial species were unique to C. balansae and C. triphyllum soil respectively. It was found that C. variegatum and C. balansae collected from areas close to each other had the highest number of common bacterial species, while C. triphyllum from the distant region shared 75 with C. variegatum and 19 with C. balansae. Metagenomics analysis reveals that in the rhizophere of C. variegatum, C. balansae and C. triphyllum, Actinobacteria is dominant at phylum level. Likewise, in C. variegatum soil, Nitrosocosmicus and halophilic Halobacter were found to be the dominant archaea. In the soils of C. triphyllum and C. balansae Saccharomycetales were detected, while Cryptococcus neoformans var. grubii H99 was exclusively detected in C. balansae soil. Significant difference (p<0.05) was observed in C. variegatum rhizosphere soil in terms of organic carbon (C%) and carbon mineralization from the other two soil samples. Significant differences were observed in all three soils in terms of nitrogen content, and the C. triphyllum rhizosphere soil was significantly different from the others in terms of available phosphorus content (p<0.05). This study showed that biological as well as the physico-chemical properties of the rhizosphere soil regulate soil microbial diversity and density and by extension influences their activity which evidently manifests itself in carbon and nitrogen mineralisation.