Canada is renowned as a nation with vast areas of productive farmland. Over the past four decades, yields of major broad-acre crops like wheat, barley, canola, maize and soybeans have increased, and continue to do so. Supporting the progress in yield improvement for most of these crops has required greater inputs of nitrogen. But concerns are also increasing about nitrogen losses in several forms with diverse environmental impacts.
Canadian scientists have developed a detailed Agricultural Nitrogen Budget. This budget is based on a combination of data from the agricultural census and government statistics, and the use of process-based models to estimate losses and yields of pastures. Inputs include fertilizer, manure, biological fixation, and deposition from the atmosphere. Outputs include crop removal in food and feed crops, as well as losses in reactive forms: ammonia and nitrous oxide emitted to the air, and nitrate lost by leaching.
A recent paper based on this Budget indicates a nitrogen use efficiency of 73%; that is, the amount removed by harvested crops and from pastures amounted to 73% of total inputs in 2016. It also indicates that losses of reactive forms of nitrogen as a fraction of total N inputs decreased from 18% in 1981 to 13% in 2016. Since both inputs and crop removal have increased substantially, however, the total losses of reactive forms have not diminished (Figure 1).
More recent statistical data on crop yields suggest that the high crop nitrogen removals reached in 2016 were repeated in five of the seven subsequent seasons. This analysis shows that improving nitrogen use efficiency is possible while intensifying production. At the same time, further improvements will be needed to make these losses even smaller.
