Optimizing seeding dates and rates for canola production in the humid eastern Canadian agroecosystems

Seeding date affects crop growth and development in various ways. Optimum seeding date (OSD) increases seedling vigour such as the germination rate and percent seedling emergence, coupled with better agronomic traits including plant height, and pod and branch numbers per plant. Also, timely seeding enables earlier flowering thereby extending the reproductive growth duration and enhancing dry matter production, harvest index, seed size, thousand seed weight (TSW), and final yield. Canola seeded at optimum dates can tolerate spring frosts and avoid unfavourable hot and dry weather during the flowering period. However, the optimum period for seeding canola is largely dependent on prevailing weather conditions in a region. As canola is a cool season, spring-seeded crop in Canada and the northern USA, we hypothesize that there is a quantitative relationship between OSD and daily air temperature of a specific period from seeding to the crop establishment for canola production in the region. We carried out a field experiment to examine the effects of varying seeding dates and rates on morphological traits, canola yield, and seed quality across eastern Canada, with specific objectives to: (1) investigate the influence of seeding date and rate on stand count, yield components, yield, and seed oil and protein concentrations, and (2) develop a location-sensitive model to estimate OSD for maximizing canola yields at various regions in eastern Canada. Using the historical weather data and the experimental results across eastern Canada, a regression model of OSD as a function of average minimum air temperature in April and May at the experimental sites was derived and fit into a quadratic curvilinear function: OSD = 3.6344T2min – 32.044Tmin + 183.37 (R2 = 0.98, P < 0.01). The model was also validated with two additional years of field experimental data. Accordingly, the OSD of canola is estimated to be 24 April at Ottawa, 26 April at Guelph and Ste-Anne-de Bellevue, 29 April at Canning, 11 May at Ste-Foy, and 25 May at the Harrington site. In addition, our study indicates that increasing seeding rate may lead to increased stand mortality and reduced branch and pod numbers. Such effects may be more dramatic for early seeding than for late-seeded canola. Overall, increasing seeding rate from 2.5 to 7.5 kg ha-1 could increase seed yield for early-seeded canola, but the yield increase was not significant above a seeding rate of 5 kg ha-1. The medium seeding rate of 5 kg ha-1 was therefore recommended across the humid eastern Canadian region.