An Empirical Approach for Estimating Seeding Dates for Winter Canola in Iowa.

Corn (Zea mays L.) and soybean (Glycine max (L) Merr.) only provide significant soil cover and uptake of nutrients during the height of the growing season, rendering Iowa cropland vulnerable to erosive forces and loss of nutrients throughout the rest of the year. Replacing these bare fallow periods with growing crops can slow soil erosion and retain nutrients in the field during the fall, winter and spring. We hypothesize that in Iowa, winter canola (Brassica napus) will be a suitable crop for soil and water conservation purposes while having the potential to produce a marketable crop in mid-summer. However, establishing winter canola in the fall represents a challenge in the cooler climates of the Upper Midwest. Moreover, seeding timing greatly affects winter canola’s readiness for overwintering. This is because ideally winter canola plants should have enough time to develop at least five leaves before the occurrence of the first killing frost to maximize potential winter hardiness. Thus, determining reliable seeding dates for this crop in Iowa is needed. Here, we present an empirical approach for estimating reliable seeding dates based on historical weather data and growth data from experimental plots. A preliminary analysis with this method for Ames, Iowa, suggests that in general, winter canola seeded by 4-September will have enough heat units available for reliable establishment and growth. Seeding may be done as late as 17-September, but frost damage and winterkill is increasingly likely. This information will be crucial in assessing the agronomic and economic feasibility of incorporating winter canola into corn-soybean rotations in this state.