Effect of N fertilization timing and formulation on N2O emissions in wheat
The timing of N fertilization can strongly influence crop productivity, NUE and N2O fluxes. The study results indicated that most of the annual N2O emissions were associated with soil thawing and after major rainfalls. Therefore, enhanced-efficiency N fertilizers (EENFs) can help to proactively reduce the risk of N2O emissions with either fall or spring N applications.
The timing of nitrogen (N) fertilization can not only impact crop productivity and nutrient use efficiency (NUE), but also impacts N dynamics and nitrous oxide (N2O) emissions. In the Prairies, fall N fertilization relative to spring N applications can result in nitrification and N losses, reductions in NUE in subsequent crops, and increase in N2O emissions.
In this study, researchers wanted to improve the current understanding of N dynamics and to identify N management for mitigating soil emissions of N2O while sustaining wheat productivity. The objectives of this study were to investigate the effects of spring compared to fall N applications of conventional and enhanced-efficiency N fertilizers (EENFs) on N2O emissions and N use efficiency in spring wheat. Factors such as variations in weather, soil moisture and soil N availability also were addressed. Researchers also wanted to evaluate the effects of these N management options on wheat grain productivity, yield-based emission factors, harvest index factors, canopy greenness as NDVI and other factors.
The study was launched in the fall of 2015 at the St. Albert Research Station in Alberta, including two full cropping cycles in 2016 and 2017 and final spring measurements in May 2018. A total of 15 fertilizer treatments were compared, including conventional anhydrous ammonia and urea and EENF formulations of urease and nitrification inhibitors and a polymer coating. The N fertilizer treatments were applied in spring or fall at a rate of 89 lbs/ac (100 kg/ha) using custom-made midrow banding equipment. The control treatment received no N application, but the banding equipment was driven over the plots at the time as spring N application to provide the same soil disturbance as the other treatments. The study location inherently had high soil fertility.
Spring wheat was seeded at the same time as either fall or spring N application in all plots. Other data collected included crop yield, N2O flux measurements using a closed chamber methodology, yield-based emission factor (EFyield), fertilizer NUE, fertilizer N recovery efficiency (NRE), physiological efficiency (PE), harvest index (HI), N harvest index (NHI), and canopy greenness as NDVI to document changes in plant N status throughout the growing season.
Application timing affects NUE and emissions
Overall, the results of the study showed the timing of N fertilization can strongly influence crop productivity, NUE and N2O fluxes. There was also a strong relationship between the weather and the effects of the timing of fertilizer application in any given year. The study results indicated that most of the annual N2O emissions were associated with soil thawing and after major rainfalls, irrespective of N fertilizer and timing options. Therefore, N fertilization in mid- or late spring can significantly reduce N2O losses associated with thawing, at the same time as helping to sustain high grain productivity and NUE.
The study also showed that applying EENFs in the spring can mitigate N2O emissions while enhancing fertilizer N recovery efficiency and grain yield, even in soils that are inherently rich in plant-available N. Overall with either fall or spring N applications, EENF can help to proactively reduce the risk of N2O emissions. The use of weather forecasts for predicting major rainfalls when planning spring fertilization could be useful to prevent the detrimental effects of excessive soil moisture and further minimizing N2O emissions.
The project was funded by Agriculture and Agri-Food Canada – AgriInnovation Program, Alberta Crop Industry Development Fund Ltd., Alberta Innovates, Fertilizer Canada/Fertilizer Institute North American 4R Fund, Emissions Reduction Alberta, Saskatchewan Agriculture Development Fund, Western Grains Research Foundation, Nutrien Inc., BASF Canada Inc., Corteva Canada, and KOCH Agronomic Services. The Prairie Agricultural Machinery Institute (PAMI, Humboldt, SK) supported the establishment of the field treatment.
Thilakarathna SK, Hernandez-Ramirez G, Puurveen D, et al. Nitrous oxide emissions and nitrogen use efficiency in wheat: Nitrogen fertilization timing and formulation, soil nitrogen, and weather effects. Soil Sci Soc Am J. 2020;84:1910–1927.
https://doi.org/10.1002/saj2.20145
