Attempts to rescue yield loss in continuous canola with agronomic inputs

Citation

Harker, K.N., Hartman, M.D., Tidemann, B.D., O’Donovan, J.T., Turkington, T.K., Lupwayi, N.Z., Smith, E.G., Mohr, R.M. (2017). Attempts to rescue yield loss in continuous canola with agronomic inputs. Canadian Journal of Plant Science, [online] 98(3), 703-716. http://dx.doi.org/10.1139/cjps-2017-0337

Plain language summary

Canola is the major cash crop in Canada. Field experiments were conducted on continuous canola land (6 years) at three Canadian Prairie sites from 2014 to 2016. Our objective was to determine if more intensive seed inputs, fertilizer, fungicide, tillage or chaff removal could increase continuous canola yields compared to a “Standard Practice” (SP) treatment or maintain yields comparable to canola in a crop rotation. Recommended or 50% higher fertility levels alone or in combination with a higher seeding rate, tillage, chaff removal or additional fungicide were applied to the same plots in three successive years to determine effects after one, two and three years.

In continuous canola, blackleg disease incidence and severity were both reduced by fungicide treatment. In rotations where canola was preceded by wheat, blackleg incidence and severity were much lower than in continuous canola. None of the treatments improved continuous canola yields compared to SP after a single year. In subsequent years, canola yield increases compared to SP usually occurred as a result of additional fertilizer, seed or fungicide. In the final year, canola yield loss due to continuous canola was largely rescued by additional seed and fertilizer. Without additional inputs, and when preceded by a different crop, canola yields averaged 11% greater than the average of all continuous canola treatments.

This research demonstrates to growers, consulting agronomists and researchers that there is not likely to be a useful method of improving yield reductions in continuous canola. The best way to grow canola sustainably is to ensure that other crops are also grown on the same land.

Abstract

Recent canola acreage and production in western Canada have reached record high levels. Field experiments were conducted from 2014 to 2016 on land previously seeded to continuous canola for 6 yr at three Canadian Prairie sites. We determined that more intensive seed inputs, fertilizer, fungicide, tillage, or chaff removal could increase continuous canola yields compared with a “standard practice” (SP) treatment or match yields compared with canola in rotation. Recommended or 50% higher fertility levels alone or in combination with a higher seeding rate, tillage, chaff removal, or additional fungicide were applied to the same plots in three successive years to determine effects after 1, 2, and 3 yr of treatment imposition. In continuous canola, blackleg incidence and severity were both reduced by fungicide treatment. In rotations where canola was preceded by wheat, blackleg incidence and severity were much lower than in continuous canola. None of the treatments improved continuous canola yields compared with SP after a single year of treatment imposition. In subsequent years, canola yield increases compared with SP usually occurred as a result of additional fertilizer, seed, or fungicide. In the final year, canola yield loss due to continuous canola was largely rescued by additional seed and fertilizer. Without additional inputs, and when preceded by a different crop, canola yields averaged 11% greater than the average of all continuous canola treatments. High fertility regimes generally reduced oil content and increased protein content relative to standard fertility in continuous canola or relative to canola preceded by wheat.