Simulating nitrogen balance in Canadian agricultural soils from 1981 to 2016

Area of Science:

• Agricultural Science
• Environmental Science
• Soil Science

Background:

• Agriculture is a significant source of reactive nitrogen (N) losses, including ammonia (NH3) emissions, nitrous oxide (N2O) emissions, and nitrate (NO3-) leaching.
• These N losses impact environmental quality and agricultural sustainability.
• Understanding N budgets is crucial for mitigating negative environmental effects.

Purpose of the Study:

• To develop and apply the Canadian Agricultural Nitrogen Budget for Reactive N (CANBNr) model to estimate soil N balance across Canada from 1981 to 2016.
• To analyze trends in N inputs, N removal, and subsequent N losses (NH3, N2O, NO3-) across different Canadian agricultural regions.
• To identify regional differences in N loss contributions and inform potential mitigation strategies.

Main Methods:

• Utilized the CANBNr model, integrating data from 3487 soil landscape polygons in Canada.
• Incorporated NH3 emissions from fertilizers and manures, N2O emissions from various agricultural sources, and NO3- leaching estimated using the DeNitrification-DeComposition (DNDC) model.
• Analyzed a 36-year dataset (1981-2016) to track changes in N balance and losses.

Main Results:

• Nitrogen input from fertilizer and fixation increased faster than crop N removal nationwide between 1981 and 2016, leading to higher residual soil N (RSN) and N losses.
• In 2016, N losses per hectare were lowest in the Prairie provinces (11.7 kg N ha-1) compared to Central (43.2 kg N ha-1) and Atlantic Canada (76.5 kg N ha-1).
• Despite lower per-hectare losses, the Prairie provinces accounted for the largest share of Canadian farmland and N input, with significant N2O and NH3 losses, and showed higher growing-season NO3- leaching.

Conclusions:

• The increasing trend of fertilizer N use in Canada, especially in the Prairies, has led to elevated RSN and N leaching.
• Regional variations in N loss intensity and total N input highlight the need for tailored management strategies.
• Further interventions are required to address rising N losses and improve the sustainability of Canadian agriculture.