Search

The landfill cover is the simplest and most feasible method to control methane emissions. Besides its low gas conductivity, methane emissions can be further reduced due to the methane oxidation by soil microbes. However, ordinary soil covers have poor engineering properties, and the methane oxidation efficiency of soil and microbial methane-oxidizing bacteria is low. Biochar is a carbon-rich, black, refractory solid material obtained through pyrolysis of biomass (such as peanut shells, wheat straw, sawdust, and rice straw) under oxygen-limited conditions. Due to its porous structure, high surface area, and pH characteristics, biochar applied to soil can change the microenvironment of the soil, which in turn can affect the efficiency of methane biological oxidation. To investigate the methane oxidation efficiency of biochar-methane oxidizing bacteria modified soil, methane detectors were used to measure the changes in methane reduction rates of both sterile and non-sterile soil samples under different pH levels, methane concentrations, soil dry densities, and biochar dosages. The results showed that when the pH of the inorganic salt culture solution was 7, the methane-oxidizing bacteria had high oxidation efficiency. The methane oxidation curve at pH value 7 is located at the bottom, indicating that the methane oxidizing bacteria have the optimal methane oxidation efficiency in neutral solution (i.e., at pH value 7). When the solution reaches alkaline properties at pH value 9, the methane reduction rate of methane oxidizing bacteria is significantly lower than that at pH value 7. This suggests that the growth, reproduction, and metabolic activity of methane oxidizing bacteria are inhibited in an alkaline environment, leading to a decrease in the efficiency of biological methane oxidation. At a certain initial methane concentration, the oxidation efficiency of methane-oxidizing bacteria increases with the increase of initial methane concentration, but when the initial methane concentration exceeds a certain value, it inhibits the oxidation efficiency of methane-oxidizing bacteria. In the control group experiment without the addition of bacteria, the slope of the curve is close to zero, indicating that the methane emission reduction efficiency is significantly lower in the sterile state compared to the condition with bacteria added. Both the biochar content and dry density affect the methane reduction efficiency of methane-oxidizing bacteria. The methane reduction amplitude with the addition of biochar is greater than that without biochar incorporation. The reason for this is that biochar has a porous structure and low density. When added to the soil, it increases the porosity of the soil and reduces its density, indirectly increasing the physical adsorption capacity of methane. Therefore, the methane reduction rate is more significant. Under the same conditions, the greater the dry density of the sample, the lower the oxidation efficiency of methane. With the increase in biochar content, the methane oxidation efficiency of biochar-methane oxidizing bacteria modified soil gradually increases. When the dry density and biochar content are 1.20 g/cm³ and 15%, respectively, the methane reduction rates under sterile and inoculated conditions show more significant decreases, being 10.38% and 39.72% respectively. This demonstrates that the addition of biochar has altered the microenvironment of the landfill cover soil, enhancing the methane oxidation efficiency of methanotrophs. This research holds significant academic and practical value for reducing greenhouse gas emissions from landfills, preventing air pollution, and promoting soil carbon sequestration. [ABSTRACT FROM AUTHOR]

Alternate wetting and drying irrigation (IAWD) is one type of water-saving technology to repeatedly dry and re-flood the fields. However, the frequent alternate aerobic and anaerobic environment under IAWD has increased the reactive nitrogen gas emission in rice fields. Fortunately, biochar has been widely used to improve land productivity (including crop production, carbon sequestration, mitigation of GHG, and remediation of heavy metal pollution) in agricultural soil amendment. However, little information is available on the effects of biochar on NH3 volatilization, N2O emissions, and reactive nitrogen gas emissions in paddy rice systems, especially under IAWD. This study aims to explore the response mechanism of reactive nitrogen gas emissions to the biochar application under IAWD conditions. A two-year field split-plot experiment was conducted with the biochar application rates (0 and 20 t/hm² ) under two irrigation regimes (continuously flooded irrigation, ICF and IAWD). Two irrigation regimes were used as the main plots, whereas, two biochar additions were the subplots. Each plot was in the size of 3 m (width) × 6 m (length) that separated by the PVC barrier at a depth of 30 cm. in order to avoid the lateral flow of nutrients and water. The results showed that the IAWD increased yields by 1.7% to 5.1% (P>0.05), NH3 volatilization by 6.6% to 11.6%, and N2O emissions by 157.1% to 116.7%, compared with the ICF (P>0.05). Biochar addition at the rate of 20 t ha−1 significantly reduced the NH3 volatilization by 10.8% to 25.2% and N2O emissions by 21.6% to 24.2% (P>0.05). There was an increase in the yield by 0.2% to 12.5% and a reduction in the reactive nitrogen gas emissions by 6.1% to 11.7% in biochar combined with the IAWD, compared with the control (ICFB0). Furthermore, the inorganic nitrogen existed mainly in the form of NH4 + -N in the soil environment of rice fields, accounting for 80% to 90%. The IAWD had no significant impact on the soil NH4 + -N, compared with the ICF, whereas, a significant increase was found in the content of surface soil NO3 − -N by 50.3% to 74% and the oxidationreduction potential by 47.6% to 54.1% (P>0.05). Moreover, the biochar addition increased the soil NH4 + -N by 25.9% to 52.41% (P>0.05), and pH by 0.6% to 1%, compared with the biochar-free treatment. Principal component analysis showed a strong negative correlation between NH3 volatilization and soil NH4+ -N content, yield, and aboveground nitrogen accumulation. It indicated that the biochar addition significantly improved the soil adsorption capacity for the inorganic nitrogen, thereby reducing the NH3 volatilization losses and increasing aboveground nitrogen accumulation, ultimately leading to an increase in the yield. N2O emissions were strongly positively correlated with the oxidation-reduction potential and soil NO3 − -N. Therefore, the frequent alternate aerobic and anaerobic environment under IAWD increased the concentration of soil NO3 − -N and the oxidation-reduction potential, thereby increasing denitrification substrates and N2O emissions. Anyway, the biochar addition coupled with alternate wetting and drying can be expected to promote rice production with water saving, carbon sequestration and emission reduction, while reducing the environmental costs associated with the reactive nitrogen emissions in the paddy field. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Drainage & Irrigation Machinery Engineering / Paiguan Jixie Gongcheng Xuebao is the property of Editorial Department of Drainage & Irrigation Machinery Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)