The Impact of Dicyandiamide on N2O Emissions from Agricultural Winter Idle Rice Fields and Rapeseed Fields

The Impact of Dicyandiamide on N2O Emissions from Agricultural Winter Idle Rice Fields and Rapeseed Fields

N2O, designated by the United Nations Framework Convention on Climate Change as the third most significant controlled greenhouse gas after CO2 and CH4, has a global warming potential (GWP) ranging from 298 to 310 times that of CO2. Agriculture is one of the sources of N2O emissions, accounting for approximately 20% to 30% of the total N2O emissions on the Earth's surface annually and contributing to 60% of anthropogenic N2O emissions. N2O emissions from agricultural soils mainly result from nitrification and denitrification processes. The main factors affecting N2O emissions from agricultural soils include soil temperature, soil moisture, soil texture, soil pH, fertilization, and tillage practices. Although there are many studies on N2O emissions, most of them focus on the growing season, while N2O emissions during the winter are often overlooked due to lower temperatures and reduced rainfall. However, winter idle rice fields and rapeseed fields in temperate to subtropical regions of the Northern Hemisphere are important yet undetermined sources of N2O emissions. Rough estimates suggest that the annual N2O (measured as N2O-N) emissions from these areas are approximately 0.75 Tg. Furthermore, winter cultivation of crops such as rapeseed and wheat in dryland soils, along with fertilization processes, may lead to high N2O emissions. Additionally, even at low temperatures, high N2O emissions may occur during the winter. Studies have shown that winter idle rice fields and rapeseed fields contribute significantly to N2O emissions during the winter months, highlighting the need for proper measures to reduce N2O emissions from these areas.

The application of organic fertilizers, promotion of slow-release fertilizers, and the use of nitrification inhibitors are considered among the most effective measures to mitigate N2O emissions. Reported nitrification inhibitors include dicyandiamide (DCD), nitrapyrin, 3,4-dimethylpyrazole phosphate (DMPP), thiourea, 2-amino-4-chloro-6-methylpyrimidine (AM), 2-mercaptobenzothiazole (MBT), and acetylene. Among these, DCD is a commonly used nitrification inhibitor. Its main mechanism of action involves inhibiting the first step of nitrification, suppressing the oxidation of NH4+ to NO3−, which can lead to the production of N2O. By reducing the production of NO3−, DCD can also inhibit the production of N2O during denitrification, thus reducing N2O emissions. Numerous studies have reported the reduction of N2O emissions with DCD application. Research indicates that the combined application of DCD and urease inhibitors can effectively reduce N2O emissions during the rice growing season, with a one-third reduction observed compared to the control group. Studies conducted by Ma et al. in rice fields showed a decrease in annual total emissions by 29.5% to 31.3% with DCD application. Similarly, studies by Di et al. in high-nitrogen grassland soils in New Zealand demonstrated the effective reduction of N2O emissions with DCD application.

However, there is limited research on the effects of DCD on winter idle rice fields and winter crops. The significant temperature fluctuations during winter and factors such as freeze-thaw cycles may promote other processes that result in N2O emissions, while the inhibitory effect of DCD is greatly influenced by temperature and moisture. Studies have shown that DCD has no inhibitory effect under high moisture conditions. Additionally, there are numerous reports on the mechanism of DCD inhibition of N2O emissions. For example, studies by Di et al. in alkaline grassland soils showed that DCD inhibition of N2O emissions primarily suppressed the population of ammonia-oxidizing bacteria (AOB) and soil nitrification activity, with no significant effect on ammonia-oxidizing archaea (AOA). In soils with pH < 4.5, DCD application significantly inhibited the growth of AOA and soil nitrification activity, with no significant effect on AOB. However, these studies on acidic soils mainly focused on indoor culture experiments without the addition of external nitrogen fertilizers. Research has shown that under conditions of high nitrogen fertilization, AOB play a larger role than AOA in the nitrification process of acidic vegetable soils. Therefore, studying the effects of DCD on N2O emissions from winter idle rice fields and winter rapeseed fields can provide theoretical support for a more comprehensive evaluation of the inhibitory effects and mechanisms of DCD.

FROM ENVIRONMENTAL SCIENCE