Research at the Qiyang Red Soil Station of the Institute of Agricultural Resources and Regional Planning (IARRP) of the Chinese Academy of Agricultural Sciences (CAAS) has revealed the effects of soil manganese oxide on phosphorus components in aggregates after long-term and different fertilizer combinations, which have enriched the theoretical basis for phosphorus management in paddy fields. The relevant research results have been published in the Journal of Environmental Management.

Judicious fertilization can enhance effective supply of phosphorus in red paddy soil and reduce the environmental risk of phosphorus. Paddy soil has a strong oxidation-reduction process, and long-term flooding leads to the enhanced activity of soil metal oxides, which has a significant impact on the availability of phosphorus. However, the transformation of soil manganese oxides under different long-term fertilization and its interaction with different components of phosphorus are still unclear.

Based on two 40-year long-term location tests on organic and inorganic fertilizer application in double-cropping rice at Qiyang Station and Nanchang City, Jiangxi Province. This study analyzed the water stability and agglomeration of surface (0-20cm) and subsurface (20-40cm) soil, as well as the relationship between manganese oxide and phosphorus components in the particle size of the body and each aggregate.

The results showed that the combined application of organic and inorganic fertilizers significantly increased the content of different phosphorus components and manganese oxide in the particle size of soil aggregates, and the contribution of macro aggregates to the total amount of phosphorus. Manganese oxide is positively correlated with unstable phosphorus pools and moderately stable phosphorus pools. After long-term application of organic fertilizers, the content of manganese oxide in subsurface soil is greater than that in the surface layer. The presence of manganese oxide can alter the trajectory of phosphorus cycle through series of chemical reactions. Therefore, the reasonable application of organic fertilizers is required to avoid excessive accumulation of phosphorus and manganese oxides, thereby reducing the environmental risk of phosphorus loss. This study also opens interesting questions into investigating the quantitative measure, its role, and overall impact of Mn stoichiometry on P and P fractions of these managed rice paddies under long term fertilizations.

Surface (A, C) and subsurface (B, D) soil aggregate active phosphorus pools, intermediate stable phosphorus pools, stable phosphorus pools and manganese at the Nanchang test site (A, B) and the Qiyang test site (C, D) and the oxide relationship

Christian Kofi Anthonio, a Ph.D. graduate from the IARRP, and Huang Jing, an associate researcher at Qiyang Station, are the co-first authors of the paper, and Zhang Huimin, a researcher, is the corresponding author. This research was supported by the National Natural Science Foundation of China, the National Key Research and Development Program and the Science and Technology Innovation Fund of the Chinese Academy of Agricultural Sciences.

Paper link: https://doi.org/10.1016/j.jenvman.2023.117440