Effects of Soil Moisture and Amendments on Cadmium Availability and Greenhouse Gas Emissions

Cadmium (Cd) contamination in soil and greenhouse gas (GHG) emission represent two pressing environmental challenges that affect soil quality, agricultural productivity, human health and global climate dynamics. The development of soil amendment strategies that address both Cd pollution and the reduction of greenhouse gas emission is crucial for enhancing soil quality and promoting the mitigation and sequestration of soil-borne GHGs. Biochar (CS), with its unique structure and superior properties, is extensively employed as a soil amendment. Zeolite (Zeo) and hydroxyapatite (HAP), known for their exceptional ion adsorption capabilities, are also widely utilized in the remediation of heavy metal contamination. Water, a key component for plant growth and development, significantly influences soil physiochemical and biological characteristics, which can change the migration and distribution of Cd in the soil by affecting the soil environment, thus further affecting the absorption and utilization of Cd by plants. The interaction between different amendments and water may jointly impact the bioavailability of soil Cd and the reduction of GHGs, yet the specific effects remain to be elucidated. The effects of three soil amendments of Camellia oleifera shell biochar, zeolite and hydroxyapatite on soil Cd pollution and GHG emissions under different soil water contents were studied through laboratory incubator experiments. The results show that under high external Cd concentration (30 mg·kg^-1 CdCl₂), HAP significantly reduced the N₂O emission rate of soil by 96.14%-99.18%, followed by Zeo. HAP significantly reduced the available Cd content in soil by 43.54%-64.64%, but significantly increased the emission rates of CO₂ and CH₄. HAP can significantly mitigate soil Cd pollution and reduce the emission rate of N₂O, making it a priority for application in acidic Cd-contaminated soils. Zeo has the best remediation effect on soil polluted by Cd from CO₂ and CH₄ emission sources, especially in soil systems with high water content. Future research should explore the synergistic application of HAP with other soil amendments to achieve the dual objectives of comprehensive GHG emission reduction and soil Cd remediation.