Economic impact of residual Nitrogen and preceding crops on wheat and canola
Khakbazan, M., Grant, C.A., Huang, J., Zhong, C., Smith, E.G., O’Donovan, J.T., Mohz, R.M., Blackshaw, R.E., Harker, K.N., Lafond, G.P., Johnson, E.N., May, W.E., Turkington, T.K., Gan, Y., Lupwayi, N.Z., St. Luce, M. (2018). Economic impact of residual Nitrogen and preceding crops on wheat and canola. Agronomy Journal, [online] 110(1), 339-348. http://dx.doi.org/10.2134/agronj2017.08.0489
Plain language summary
The application of nitrogen (N) fertilizer is known to significantly improve crop yield, but knowledge of its residual effect combined with the residual effects of legume and non-legume preceding crops (PCs) on crop yield and profits in future years is limited. A 6-year study was conducted in multiple locations across western Canada in order to determine the residual effects of various PCs (field pea, lentil, canola, wheat, faba bean harvested for grain, and faba bean harvested as a green manure) and nitrogen application on the profits of wheat and canola grown in subsequent years. In the first phase of the study, canola was seeded in 2010, barley in 2011, and canola again in 2012; N fertilizer was applied at varying rates for each crop. In the second phase of the study, spring wheat was grown in 2013 and canola in 2014; no N fertilizer was applied in these years. Legume PCs were found to have a positive effect on N supply and profits for the following two crop years, but these benefits decreased over time and were almost nonexistent in phase II. Residual N fertilizer for most rates was also found to be beneficial for about two years before its effect dissipated; residual N had a positive effect on the profits of wheat in 2013, but on canola in 2014 the economic benefit was mostly with the highest application rate of N (120 kg N ha-1). The results of this study showed that although production profits are greatest with an annual fertilization program based on the production capacity of the region, under the dry conditions of the Canadian prairies excess N remaining in the soil after crop production can be used by following crops. While this residual N is not generally sufficient to optimize crop production, it reduces the economic risk from the over-application of fertilizer if N is not utilized by the crop due to adverse growing conditions that reduce crop yield and N uptake in the year of fertilizer application.
A 6-yr study was conducted across western Canada to evaluate the residual effects of preceding crops (PCs) and past N rate management on the economics of subsequent wheat (Triticum aestivum L.) and canola (Brassica napus L.). Field pea (Pisum sativum L.), lentil (Lens culinaris Medik.), canola and wheat harvested for grain, and faba bean (Vicia faba L.) grown and harvested for grain or as a green manure were direct seeded in 2009. Canola was seeded in 2010, barley in 2011, and canola again in 2012 with fertilizer N applied at varying rates for each crop. Spring wheat grown in 2013 and canola in 2014, both without N application, were used to determine residual PC and residual N effects. The positive benefit of legume PCs on the annual crop net revenue (NR) of wheat and canola crops diminished over time. Residual N from previously applied N had positive effects on annual wheat NR in 2013, but only the highest application rate contributed significantly to canola NR in 2014. The NR was greatest with an annual fertilization program based on regional production capacity, but under the dry conditions of the Canadian prairies excess N remaining in the soil after crop production could remain in the soil as residual N to be used by following crops. While generally insufficient to optimize crop production, residual N can reduce the economic risk from over-application of fertilizer if N is not utilized by the crop due to adverse growing conditions in the year of fertilizer application.