Innovative experimental design and teaching practice based on the effect of biochar-based nano-zinc on soil organic carbon sequestration

The present study aimed to investigate the regulatory effects of the interaction between novel nano-zinc materials and biochar on the soil organic carbon (SOC) pool. The impact of biochar modified with varying amounts of nano-zinc on SOC and its component fractions was systematically examined. The mechanism through which nano-zinc influences SOC transformation under biochar input was further elucidated through the analysis of carbon-transforming enzyme activities.

A three-year experiment (2021-2023) was conducted using sandy loam soil and rice (cultivar ‘Nanjing 9108’). A total of seven treatments were established, including a control with no amendment (CK), biochar alone (BC, 20 t/hm2), and five treatments with biochar loaded with varying amounts of nano-zinc (0.5% to 2.5% nZnBC, applied at 20 t/hm2 biochar with 100–250 kg/hm2 nano-zinc). The contents of soil organic carbon (SOC), readily oxidizable carbon (ROC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), and particulate organic carbon (POC) were systematically measured. Changes in soil available zinc (AZn) content and the activities of key carbon-transforming enzymes (FDA hydrolase, β-glucosidase, and sucrase) were analyzed.

The findings indicated that the application of biochar-based nano-zinc led to a significant enhancement in SOC, as well as the abundance of active carbon fractions. Comparatively, SOC content exhibited a 21.64% increase, reaching 105.44% over the three-year period, with this rise becoming more pronounced over time. The contents of ROC, DOC, MBC, and POC in treatments with biochar and biochar-based nano-zinc were also significantly higher than in CK. However, no consistent or significant trend was observed for these indicators between the biochar-based nano-zinc treatments and the BC treatment alone. Concurrently, biochar-based nano-zinc substantially augmented soil AZn content, reaching levels up to 339.23 times higher than CK. Soil AZn content exhibited a significant positive correlation with SOC, ROC, DOC, and POC contents. Enzyme activity analysis revealed that the addition of biochar-based nano-zinc primarily affected SOC sequestration by regulating the activity of key soil carbon cycle enzymes. A substantial inhibition of FDA hydrolase and sucrase activities was observed, accompanied by a low-concentration promoting effect and a high-concentration inhibitory effect on β-glucosidase activity. Principal component analysis further confirmed that nano-zinc, by enhancing soil AZn content, inhibited the activity of enzymes related to carbon transformation. This inhibition reduced the microbial mineralization and decomposition of SOC, ultimately promoting SOC accumulation and sequestration.

Biochar-based nano-zinc, a novel composite material, effectively coordinated soil zinc nutrient supply and carbon sequestration processes. A viable technical approach for simultaneously enhancing paddy soil fertility and strengthening soil carbon sink function is provided by the mechanism of “enzyme-inhibiting carbon sequestration.” This approach demonstrates significant application potential. Moreover, this research introduces the current research hotspot into comprehensive experiments integrating soil science, soil fertility science, and fertilizer resource development and utilization. This integration enables the establishment of a connection between the prevailing topical issue of “soil carbon sequestration” and the foundational theoretical knowledge derived from their professional courses. It is particularly beneficial for students majoring in Agronomy as well as Agricultural Resources and Environment. This experiment enables students to apply fundamental knowledge from multiple specialized courses, including Crop Cultivation, Soil Science, Agricultural Chemical Analysis, and Statistical Analysis with Software Applications, thereby enhancing their ability to analyze and solve practical problems.