Boron was one focus of the Ultimate Canola Challenge in 2015.
One challenge with boron is the hot water extraction (HW) soil test commonly used to test boron levels does not seem to be a reliable indicator of available boron. A 1999 study by Rigas Karamanos showed no relation between HW boron levels and canola yield. Soil analysis will continue to use the HW test until some other reliable method is available.
Karamanos also ran canola tissue analysis at early flowering for 18 sites, and it too was unrelated to canola seed yield — offering no viable alternative in interpreting the obtained yield results.
Karamanos ran soil samples for 19 sites in the study. Trials compared broadcast and incorporated, seed placed, soil top dress and foliar applied boron. In 14 boron fertilizer trials, no trial showed any yield benefit from boron fertilizer — even when HW boron tests were as low as 0.15 ppm. See Figure 5 taken from Karamanos’s report.
Organic matter seems to provide enough boron to meet the needs of most canola crops. Fields with very low organic matter and dry conditions would be the most likely to show yield-reducing levels of boron deficiency.