Effect Of Different Amendments On Soil Microbial Ecology

Soil amendments are usually used to improve soil physico-chemical properties, nutrient cycling and crop yield. However, there have been little studies on the effect of soil amendments on soil microbial ecology. In this research, we investigated the effect of mushroom residue, calcium cyanamide, activated carbon, lime, charcoal, and urea on underground ecosystem. The main results are as follows:(1) Pot experiments have been performed to investigate the effect of two amendments, mushroom residue and activated carbon(AC), on soil microbial community in ryegrass rhizosphere. The results showed that adding mushroom residue and AC could increase soil microbial biomass and total-phospholipid fatty acid(T-PLFA). For mushroom residue,5% doses had more effect on microbial biomass than 1% doses, while 1% and 5% AC had similar effect on microbial biomass. The phospholipid fatty acid(PLFA) results showed mushroom residue didn't alter soil microbial community structure, but AC had significant effect on soil microbial community structure. The effect of AC was more obvious as the amount of AC increase. Besides, the two amendments increased the yields and nitrogen content of ryegrass. The above results indicated that AC had positive role to change microbial community composition structure, whereas mushroom residue could only increase microbial biomass.(2) The change of microbial community is considered as the major obstacle of continuous Rehmannia (R.) glutinosa cropping. In this work, pot experiments have been performed to investigate the change of soil microbial community in R. glutinosa cultivation under treatment with different amendments, i.e., mushroom residue(1%), calcium cyanamide (0.05%CaCN2), and activated carbon(1%AC). The microbial biomass, T-PLFA, and PLFA under different treatments have been determined to analyze the characteristics of microbial community. The results showed that there were various degrees of increase in the yield of R. glutinosa under the addition of different amendments. However, mushroom residue only increased the microbial biomass, but had no significant effect on the microbial community structure; CaCN2 showed obvious effect only at the initial stage, and the microbial community structure quickly recovered; AC amendment positively affected the microbial community structure during the whole planting process. Therefore, we concluded that AC is more effective in relieving the obstacles of continuous R. glutinosa cropping compared to other amendments.(3) Understanding the mechanism and key controlling factors of nitrification in highly acidic soils is important from both ecological and environmental perspectives. Many acid soils are also characterised by vegetation that produces polyphenolic and terpene compounds that inhibit microbial activity. We investigated the potentially ameliorative effects of lime, charcoal, and urea additions on soil nitrification and carbon substrate utilization (using the MicroResp method). Four soils were studied from widely different environments but with similar pH and inputs of phytochemicals to determine the relative effects of these potentially controlling factors. The addition of charcoal had no significant effect on net nitrification, but charcoal significantly increased soil basal respiration and altered C substrate utilization in the two Scottish soils. Urea greatly increased nitrification in both the Chinese soils, but there was no effect of urea on nitrification in the two Scottish soils. Lime application increased nitrification in all the soils except for the Chinese mixed forest soil. Multivariate analysis of the C source utilization data revealed that lime altered C substrate utilization more than urea or charcoal in these highly acidic soils. Our results suggest that acid-tolerant nitrifiers do exist in these soils and have potential for high activity and pH (lime addition) and N-substrate (urea) most often increased nitrification. However, no single factor controlled nitrification in every soil suggesting an interaction between abiotic and nitrifier community composition as a result of land use and soil type interactions.