Boron Deficiency in Oil Seed Rape
Canola (oil seed rape), like all its relatives in the Brassica family, has a very high boron requirement and is severely affected by boron deficiency. Canola seed production is critically dependent on boron—so much so that grain yields have been doubled when 2 lbs of boron per acre were applied to canola fields that showed no visual abnormalities.
Canola needs more boron through all growth stages—vegetative and flowering—than most other crops. Ensuring that canola has adequate boron will:
- Stimulate root growth and early establishment
- Enhance vegetative growth and speed maturity
- Increase branching and flowering
- Increase flower retention and pollen germination
- Enhance nitrogen utilization to increase oil percentage
- Increase the number of pods that set and fill
Although boron deficiency can markedly affect vegetative growth, it is more usual to find that yields are reduced by the deficiency even when the plants show no obvious symptoms. This is probably due to the fact that boron is required for pollination and because a slight deficiency can result in poor seed set, even though pods may be formed. Brown necrotic areas which form in the pith of the stem may be one of the earliest signs of boron deficiency.
When the deficiency is severe the new leaves will be very deformed; they may have cracked petioles and be bent back. Stem elongation will be restricted, the plants will be stunted, and ultimately the growing point may die. Branching may be excessive.
How much boron is enough?
- Canola is grown in all types of soils and in all climates, from Alaska and Canada all the way to Florida. Consequently, boron fertilization needs and practices vary.
- Many growers simply apply boron with their other preplant incorporated fertilizers. This practice may not be effective on fall-seeded fields with soils that are prone to leaching or fixing boron.
- Research and experience show that multiple—or preferably, foliar—applications made up to flowering consistently result in the highest yields.
Rates of boron fertilization should be based on soil tests and/or plant analyses, along with field histories, yield goals, and application methods.