The Innovation Team of Fertilizer and Fertilization Technology of the Institute of Agricultural Resources and Regional Planning (IARRP) of the Chinese Academy of Agricultural Sciences (CAAS) analyzed a series of data gathered in joint positioning experiments and from demonstration sites and farmer surveys conducted across multiple sites in southern China, and has quantified the effects of green manure on for stable and high grain yield green manure in paddy fields. It has also studied the effects of saving fertilizer, increasing efficiency, and reducing nitrogen losses by cultivating soil, and explored its mechanisms.

The relevant results were published in the international journal "Resources, Conservation & Recycling" under the title "Southern China can produce more high-quality rice with less N by green manuring".

Green manure plays an irreplaceable role in constructing a modern agricultural planting system and achieving the combination of field use and nourishment. In recent years, China has been promoting actions such as storing grain in technology, reducing chemical fertilizers, and improving the quality of cultivated land. Green manure is an important technical and material guarantee. However, there is a lack of research and quantification on the regional scale of the contribution and mechanism of green manure in terms of increasing yield, saving fertilizer, improving soil fertilizer, and reducing the environmental burden. Starting in 2008, with the support of dedicated projects and programs for green manure, a series of green manure-rice positioning experiments were established in southern rice-growing areas, and a large number of on-site demonstrations were carried out. Farmers' acceptance of green manure has gradually increased, and the green manure planting area has steadily rebounded. The accumulation of a large number of positioning experiments and research data over the past decade has provided conditions for quantifying the effect of green manure at the regional level.

This study comprehensively utilized methods such as agroecosystem model, life cycle assessment, and microbial co-occurrence network analysis to comprehensively review the research results collected over many years and locations in rice-growing areas, and systematically presents the effects of green manure on reducing fertilizer use, nurturing soil, improving efficiency and quality, and reducing emissions and losses. The study quantified the potential of green manure to reduce fertilizer use and increase the efficiency of rice fields. Compared with winter fallow with conventional chemical fertilization, winter green manuring with conventional fertilization and 20% reduction of nitrogen fertilizer, rice yields increased by 5.7% and 3.8%, respectively; the corresponding nitrogen fertilizer utilization rates increased by 7.8% and 12.6%. When nitrogen was reduced by 40%, grain yield was same as winter fallow with conventional fertilization, and the nitrogen fertilizer utilization rate increased by 15.8%. With no nitrogen fertilizer applied, the yield was 81.1% of that of conventional fertilization (n=5821). The study confirmed that green manure effectively enhanced the nutritional quality of rice, and when combined with fertilizer, nitrogen could be reduced by 40%, and the total amino acid and essential amino acid contents of rice increased by 62.6% and 30.7%, respectively. The study also demonstrated the reduction of losses and emissions in rice fields with green manure. When green manure was combined with a 40% reduction in chemical fertilizers, carbon footprint, reactive nitrogen loss, and nitrogen footprint decreased by 30.86%, 19.20%, and 9.65%, respectively.

Long-term positioning test distribution and field scenarios

The yield effects of green manure combined with different proportions of chemical fertilizers (a and b), the amount of fertilizer applied by green manure users (c and d), the protein and amino acid content of rice under green manure with different proportions of chemical fertilizers (e and f)

Dr. Songjuan Gao from the School of Resources and Environmental Sciences of Nanjing Agricultural University is the first author of this article, and researcher Cao Weidong from the IARRP is the corresponding author of this article. The research was jointly funded by the "14th Five-Year Plan" National Key R&D Project (2021YFD1700200), the National Green Manure Industry Technology System (CARS-22), and the National Natural Science Foundation of China (42007071).

Citation: Gao, S.J., Zhou, G.P., Chang, D.N., Liang, H., Nie, J., Liao, Y.L., Lu, Y.H., Xu, C.X., Liu, J., Wu, J., Han, S ., Wang, H., Liu, C.Z., Lv, Y.H., Huang, Y.B., He, C.M., Geng, M.J., Wang, J.H., He, T.G., Li, Z.Y., Liang, H., Li, S., Rees , R.M., Thorup-Kristensen, K., Cao, W.D., 2023. Southern China can produce more high-quality rice with less N by green manuring. Resources, Conservation & Recycling, 196, 107025.

Paper link: https://www.sciencedirect.com/science/article/pii/S0921344923001611