In paddy soil, rice straw serves as an organic amendment that releases N, P, K, and other essential nutrients upon decomposition; thus, the addition of rice straw not only increases SOM content, but also maintains soil fertility. However, straw addition can influence greenhouse gas (GHG) emissions (mainly CH₄ and CO₂) in paddy soil. Studies on  CO₂ and CH₄ emissions from paddy soils have generally focused on full fertilizer applications, which do not correspond to the application patterns used in practice. According to high-yielding rice cultivation practices in China, fertilizer application is usually split into basal and top-dressing during the early tillering stage and the mid-season, respectively. Generally, splitting fertilizer application improves N and/or P use efficiency owing to a decrease in their relative losses. Therefore, split fertilization may lead to soil C sequestration and to the reduction of GHG emissions.

Researchers in the Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) investigated split N and P addition decreases straw mineralization and the priming effect of a paddy soil. The team found that the application of split NP fertilization along with straw addition improved microbial enzyme activity, yielding the highest positive priming effect (PE) for CO₂emission. In contrast, compared with the control (no addition), split NP application decreased the positive PE for CH₄ emission. Therefore, the straw-C-derived total CO₂ equivalent emission was decreased by split NP application.

This study also showed that the application of straw combined with split NP addition appeared to provide an optimal supply of C, N, and P for the stoichiometric microbial nutrient requirement (i.e., met the require C:N:P ratio), which most likely decreased microbial mining of nutrients from SOM and therefore decreased the PE for  CO₂ emission. In addition, P fertilizer application increased the  CH₄ oxidation potential and reduced the total  CH₄ emission. The important implication is that “the split mineral fertilizer application may be considered as an optimal soil fertility management measure to increase exogenous C source anabolism and mitigate greenhouse gas emission from the paddy field ecosystem.” said Zhu Zhenke, an associate researcher in ISA.

This research was funded by the National Science Foundation of China (41430860, 41877104 and 41811540031); Natural Science Foundation of Hunan Province (2019JJ30028); Innovative Research Groups of the Natural Science Foundation of Hunan Province (2019JJ10003), the Youth Innovation Team Project of the Institute of Subtropical Agriculture, Chinese Academy of Sciences (2017QNCXTD_GTD), the Hunan Province Base for Scientific and Technological Innovation Cooperation (2018WK4012), JSPS and NSFC under the Japan-China Scientific Cooperation Program, and the Public Service Technology Centre, Institute of Subtropical Agriculture, Chinese Academy of Sciences.

The study, titled “Split N and P addition decreases straw mineralization and the priming effect of a paddy soil: A 100-day incubation experiment” has been published in Biology and Fertility of Soils, and details could be found at https://link.springer.com/article/10.1007/s00374-019-01383-6 

Figure 1. The CO₂-equivalents of  CH₄ and  CO₂ emission, and the amount derived from straw and SOM in different treatments at the end of incubation

Figure 2. The structural equation model (SEM) showing the effects of multiple factors on the priming effect for  CO₂ and CH₄

Contact: Zhenke Zhu

E-mail: zhuzhenke@isa.ac.cn

Institute of Subtropical Agriculture, Chinese Academy of Sciences