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.

This study primarily aimed to enhance rice’s utilization efficiency of nitrate nitrogen, which is a crucial nutrient for plant growth and development. By exploring the effects of molybdenum nanoparticles on key enzyme activities involved in nitrogen metabolism and nitrate nitrogen accumulation in rice, we aimed to provide a scientific basis for the development of new strategies to improve the nitrogen use efficiency of rice. This is particularly important for enhancing rice production and quality, as nitrogen is often a limiting factor in rice growth and yield.

To achieve this objective, a hydroponic experiment was conducted using rice plants. The experiment consisted of nine treatments to comprehensively evaluate the effects of molybdenum nanoparticles and sodium molybdate on rice nitrogen metabolism and growth. The treatments were as follows: 1) no molybdenum application as the control group (CK); 2) sodium molybdate at a concentration of 50 μg Mo/L (T1); 3) sodium molybdate at a concentration of 100 μg Mo/L (T2); 4) sodium molybdate at a concentration of 200 μg Mo/L (T3); 5) sodium molybdate at a concentration of 400 μg Mo/L (T4); 6) molybdenum nanoparticles at a concentration of 50 μg Mo/L (T5); 7) molybdenum nanoparticles at a concentration of 100 μg Mo/L (T6); 8) molybdenum nanoparticles at a concentration of 200 μg Mo/L (T7); and 9) molybdenum nanoparticles at a concentration of 400 μg Mo/L (T8). Rice plants were grown in a hydroponic system and subjected to these different treatments to investigate the effects of molybdenum nanoparticles and sodium molybdate on key enzyme activities involved in nitrogen metabolism, nitrate nitrogen accumulation, nitrogen content in rice stems and leaves, and rice dry matter accumulation. Specifically, we measured the activities of three key enzymes involved in nitrogen metabolism: nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthase (GOGAT). We also assessed the nitrogen content in rice stems and leaves, as well as rice dry matter accumulation, to evaluate the overall effects of molybdenum nanoparticles and sodium molybdate on rice growth and development.

The results of the experiment showed that molybdenum nanoparticles had a significantly greater promoting effect on the activities of NR, GS, and GOGAT in rice leaves compared with sodium molybdate at the same concentration. This indicated that molybdenum nanoparticles were more effective in enhancing the nitrogen metabolism of rice than sodium molybdate. Furthermore, both sodium molybdate and molybdenum nanoparticles promoted nitrogen content in rice stems and leaves, as well as rice dry matter accumulation. However, molybdenum nanoparticles showed significantly better promotion effects on dry matter accumulation in both above-ground and underground parts of rice than sodium molybdate. These findings suggest that molybdenum nanoparticles can improve the nitrogen absorption and utilization of rice and promote rice growth and development. By providing a new solution for enhancing rice production and quality, this study has promising application prospects in agricultural production. The use of molybdenum nanoparticles as a fertilizer additive or as a standalone nutrient source can potentially increase rice yields and improve rice quality, leading to increased food security and improved livelihoods for rice farmers.

Incorporating contemporary research issues into educational curricula is essential in bridging the gap between theoretical knowledge and practical application. This study is designed to integrate the emerging topic of “novel fertilizers” with the fundamental theories of soil science and fertilizer resource development. In particular, this study explores the efficacy of biochar-based zinc fertilizers in increasing the zinc content in rice grains, an essential micronutrient that is often deficient in common diets. Biochar, as a carbon-rich product derived from the pyrolysis of organic materials, is used in this experiment as a carrier for zinc to enhance the soil microenvironment around rice roots, facilitating the uptake of zinc into the rice plants.

This experiment involved the preparation of biochar-enriched zinc fertilizers and their application to rice paddy fields. The biochar was derived from wheat straw pyrolyzed at 600℃, and zinc oxide nanoparticles (nZnO) were loaded onto the biochar using zinc acetate as a precursor. XRD and SEM analyses confirmed the successful loading of nZnO onto the biochar surface. The pot experiment included eight treatments: (1) no biochar and nZnO (T1), (2) 20 t/ha biochar (T2), (3) 100 kg/ha nZnO (0.5%nZnO, T3), (4) 20 t/ha biochar + 100 kg/ha nZnO (BC+0.5%nZnO, T4), (5) 200 kg/ha nZnO (1.0%nZnO, T5), (6) 20 t/ha biochar + 200 kg/ha nZnO (BC+1.0%nZnO, T6), (7) 200 kg/ha nZnO (2.0%nZnO, T7), and (8) 20 t/ha biochar + 200 kg/ha nZnO (BC+2.0%nZnO, T8). Students measured rice growth, yield, and nutrient content in the plants and grains, analyzing zinc fertilizer utilization and the impact of biochar-based nano-zinc on soil nutrients. The subsequent analyses focused on the bioavailability of zinc in the rhizosphere, i.e., the root zone of the plants.

The results from this study indicate that the application of biochar-based zinc significantly improved the nutrient availability within the rhizosphere. The study observed that the concentration of available zinc in the root soils markedly increased, which, in turn, promoted the accumulation of zinc in both the rice plants and the harvested grains. This increment in zinc content is crucial, considering the role of zinc in enhancing immune function and overall human health. Further analysis confirmed that biochar-based nano-zinc exerted a considerable impact on the microenvironment of the root zone, modifying physical and chemical soil properties in a manner conducive to nutrient uptake. Statistical analysis employing advanced software tools supported these findings, demonstrating a clear trend of enhanced zinc accumulation due to the novel fertilizer application.

This study not only confirms the potential of biochar as an effective carrier for micronutrients like zinc but also illustrates the transformative impact of integrating innovative agricultural inputs with traditional farming practices. Through this study, students engaged in soil science, plant nutrition, agricultural chemical analysis, and related disciplines can enhance their ability to apply theoretical knowledge in analyzing and solving real-world agricultural challenges. In conclusion, the study highlights the significant potential for novel zinc-enriched biochar fertilizers to improve crop micronutrient density. This approach not only addresses the global challenge of micronutrient deficiencies in diets but also offers a sustainable and efficient strategy for resource utilization in agriculture. The experiment thus serves as a valuable model for educational practices, fostering a deeper understanding and practical skills among students in the field of agricultural science.