# Controlling Conditions of the One-Dimensional Consolidation Test on Peat Soil
## 5 Effect of thymol  
Previous studies have shown that there is abundant plant debris in peat soil [33], that is largely composed of lignin, cellulose, and other macromolecular organic compounds. Macromolecular organics form monosaccharides (C\({}_{6}\)H\({}_{12}\)O\({}_{6}\)) through the action of enzymes, which then escape because of the generation of CO\({}_{2}\) that is caused by microbial activity [34; 35; 36]. Equation (1) shows the reaction equation under proper ventilation, whereas Equations (2) and (3) are the reaction equations under poor ventilation conditions. The escape of CO\({}_{2}\) leads to a decrease in the total organic matter and a change in the loss on ignition. Therefore, loss on ignition characterizes the decomposition of organic matter from a macro perspective.  
\[\text{C}_{6}\text{H}_{12}\text{O}_{6}\xrightarrow{\text{Microorganism}} \text{CO}_{2}\uparrow+\text{H}_{2}\text{O}+\text{Energy} \tag{1}\]  
\[\text{C}_{6}\text{H}_{12}\text{O}_{6}\rightarrow\text{CH}_{3}\text{CH}_{2} \text{CH}_{2}\text{COOH}+\text{CO}_{2}\uparrow+\text{H}_{2}\uparrow \tag{2}\]  
\[\text{CO}_{2}+\text{H}_{2}\rightarrow\text{CH}_{4}\uparrow+\text{H}_{2}\text{O} \tag{3}\]  
Through chemical analysis, [PERSON] and [PERSON] [37] found that due to the activity of soil microorganisms, macromolecular organics were mineralized, and the soil gradually released nitrogen from the organic matter in the form of the ammonium ion (NH\({}^{4+}\)) [38; 39]. This transformation process is shown in Figure 4[40]. [PERSON] and [PERSON] [41] verified the \"flow\" process of nitrogen after the death of barley plants using the isotope marking process. They determined that the annual mineralization rate of nitrogen was 6.3-7.4%. At present, the characterization of the decomposition degree of organic matter based on the nitrogen content has been widely used in agriculture. For example, [PERSON] et al. [42] examined the decomposition process of lake sediments by measuring the inorganic nitrogen content as well as other indicators. [PERSON] et al. [43] analyzed the decomposition process of mangrove leaves by measuring the inorganic nitrogen content. Characterizing the decomposition degree of organic matter from a micro perspective using the total nitrogen content (TN) is therefore feasible, i.e., the decomposition degree of plants increases with an increase in the TN [44; 45].  
Thymol solution was used to control microbial reproduction and to reduce biological oxidation in peat soil test. During the analysis, the TN content and burnout were used to characterize the degree of organic matter bio-oxidation; the test results are shown in Figure 5.  
Figure 4: Two patterns of nitrogen cycling.  
Figure 5a shows the percentage of loss on ignition before and after the test. The TN content was tested using a JR-600M soil nutrient rapid tester produced by CHINA JIRU YIQI (Weifang, Shandong), and the percent increase is shown in Figure 5b. The reduction of LOI and the increase in TN in the test group with the thymol solution were smaller, which shows that the sample that had been soaked with thymol solution effectively inhibited the decomposition of organic matter during consolidation. For a test lasting 7 days, spraying the thymol solution (method 1) is effective. For the 60-day test, the effect of immersing the sample in a thymol solution (Method 2) is more obvious, which may be because the spray method only works on the surface of the soil sample and because the inhibitory effect only lasts for a short time.  
The filter paper on the surface of the soil sample without thymol (Figure 6) exhibited a brown substance after the test. This brown substance was the organic high-molecular compound (humus) that was formed in the humification process in peat soil [18]. The filter paper on the samples treated that had been with thymol remained white, verifying that the thymol solution inhibited the biological organic oxidation.