Abstract
Split application of nitrogen (N) fertilizers during different crop growth stages to fulfill the crop N requirements reduces soil mineral N concentrations and improves the efficiency of crop N fertilizer use, and can decrease nitrous oxide (N2O) emission from the soil. However, inconsistent results regarding N2O emissions have been reported in rainfed areas. Furthermore, few long-term studies have explained the effects of split N application on soil methane (CH4) flux, thus limiting complete assessment of the effects of split N application on total greenhouse gas (GHG) emissions. Therefore, long-term monitoring is urgently required to understand the impacts of split N application on GHG emissions in rainfed areas. In this study, a 6-year field experiment was conducted in a rainfed maize (Zea mays L.) field in Northeast China. The experiment included three treatments: no N application representing control (CK), single application at the sowing stage of maize (SU), and split N at the sowing and jointing stages at a ratio of 1: 2 (SF). Between the sowing and jointing stages, N2O emissions were significantly higher in SU than in SF. However, high N2O emissions were observed in SF for 1 month after N application at the jointing stage possibly because the time of N application coincided with optimum precipitation and soil temperature conditions, which stimulated N2O emissions. Overall, the total N2O emissions showed no significant difference between SU and SF. During the study period, split application of N fertilizer did not significantly affect the cumulative CH4 flux. Compared to CK, the yield-scaled GWP in SF treatment increased by 18.7% (p < 0.05). Ammonia (NH3) volatilization in SF was 272% higher than that in SU. The findings indicated that split N application exhibited an environmental risk by increasing the yield-scaled GWP and NH3 emissions in the field. Thus, this study suggested that single N application applied in the sowing stage should be employed in rainfed fields to mitigate the yield-scaled GWP and NH3 emissions, and maintain efficient maize yields.
Highlights
Nitrous oxide (N2O) is a potent greenhouse gas (GHG) with a global warming potential (GWP) that is 265 times more than that of carbon dioxide (CO2) in a 100-year timescale; it significantly destroys the stratospheric ozone layer (IPCC, 2013)
In May 2012, a dry period persisted from May 3 to 29, during which 7.6 mm of precipitation was recorded, and the soil waterfilled pore space (WFPS) at 0–5 cm depth decreased to 24% on May 28
During July 5–24 2015, precipitation was not recorded, and the soil WFPS gradually declined to 10% on July 24
Summary
Nitrous oxide (N2O) is a potent greenhouse gas (GHG) with a global warming potential (GWP) that is 265 times more than that of carbon dioxide (CO2) in a 100-year timescale; it significantly destroys the stratospheric ozone layer (IPCC, 2013). Fertilized soil is a primary source of N2O (Smith et al, 1998; Thompson et al, 2019); using suitable agricultural management measures can effectively reduce N2O emissions (Shi et al, 2013). Delaying the application of N fertilizers to maize during the growing season can effectively reduce N2O emissions in rainfed systems (Dell et al, 2014). The authors of this study could not draw a conclusion on the response of CH4 flux to conventional N application (180 kg N ha−1) in upland cropping systems in the study area. Increased upland field studies were required to reduce the uncertainty of the effects of N application on soil CH4 fluxes
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