There has been a great deal of debate about the need for boron on spring canola. It is well documented that boron plays a critical role in proper canola pollination and seed set. This has created quite a bit of interest from growers who have been experimenting with foliar boron applications at early-flowering. Also driving this interest, were the results of an on-farm trial by the first winner of the Canola Yield Challenge in 2005, Ray McCabe of Shelburne. Ray achieved the highest yields in treatments in which boron was included.
Western Canada Results
However, Dr. Rigas Karamanos, a canola fertility expert based in western Canada, concluded after reviewing all the research on boron in canola that there is little evidence that supports the use of boron in canola. Dr. Karamanos also supported OMAFRA’s recommendation that the current boron soil test is of no value in assessing the boron status of soils.
Conditions That Favour Boron Deficiency
Ontario soils contain sufficient boron to meet the needs of most crops. Canola and alfalfa both have a high requirement for this micronutrient. Deficiencies in Ontario have only been seen in alfalfa. As management practices and genetics move the yield bar higher in canola and alfalfa, the removal of boron from soils is increasing.
In the soil, boron moves with soil water, so it is subject to leaching. Sandy or gravelly soils, soils with very high pH (pH > 8.5), and low organic soils are prone to low boron levels. Soils east of the Niagara escarpment are particularly prone to be low in boron. Boron shortages on clay and clay loam soils are rare. Organic matter is an important source of boron. Under dry conditions, release of boron from organic matter and the movement in soil water is reduced. Deficiency is more evident on droughty soils under dry conditions. Excessive applications of sulphur have been shown to lower the boron levels in canola plants by reducing the uptake of boron through the roots.
Temperature At Flowering
In a 2007 – 2008 study by Dr. Hugh Earl, University of Guelph, boron applied at early-flower improved yields by 5.7% in 2007, but only marginally in 2008. He surmised the reason for the different response between years, may be related to temperature during flowering and early-pod fill. Canola is a cool season crop, and it has been recognized that 29°C is a critical temperature for canola during flowering (Figure 1). High temperatures interfere with proper flower formation, pollination and results in increased pod abortion. While 2007 was a much more stressful year, with high temperatures during flowering, 2008 had no days over 30°C during pollination. In a 2010 controlled temperature greenhouse study, Dr. Earl was able to show that boron can help mitigate the effects of high temperatures during flowering, reducing pod abortion.
Note: Exposure to daytime / night temperatures of 20/18, 28/18, 35/18 °C for 10 days. Seed yield in grams per plant.
Ontario Field Trials Support Foliar Boron Application
In a 3 year (2008-2010) on-farm strip trial, foliar boron applied at early-flower increased yield by 94 lb/ac (3.5%) over the check (Figure 2 – Canola Yield Response To Foliar Boron). Boron application improved yields 78% of the time and improved returns 40% of the time (using a product cost of $5.50/ac + $10/acre application). Trials were field length with 2 replications. Favourable weather during the growing season in all three years of the trial, offered little stress to canola resulting in above average to phenomenal canola yields (1 – 1.6 t/acre).
Figure 1. Daytime – Night time temperature impact on canola yield.
Figure 2: 2008-2010 Canola Yield (lb/ac) Response to Foliar Boron
Options For Applying Boron
Banding or seed row placed boron can be toxic to plants, and is not recommended. In alfalfa the recommendation to correct a boron deficiency is to broadcast 1 – 2 kg/ha of actual boron, applied annually. The benefit of broadcast and incorporated boron in canola has not been tested in Ontario. If boron is to be applied foliar in canola, the recommended rate is 0.3 – 0.5 lb/ac (0.34-0.56 kg/ha) of actual boron.
Many other field crops have low boron requirements and can be injured by boron applications. Most notable are the grass family, dry beans, cereals, soybeans, corn, and peas. If these crops are to follow in the rotation, do not apply boron the previous fall, or exceed the recommended rate in the previous alfalfa or canola crop.
Manure can also be a source of boron. Manure applied to sandy areas or other suspect areas can also provide organic matter. Boron should not be applied with a herbicide, without first consulting with a specialist.