Foliar Boron Application Increases Yield and Alters Pod Distribution in Spring Canola.

Foliar boron (B) is often applied to spring canola during early flowering, but yield benefits from this practice have been inconsistent and the physiological basis of the yield benefit is unknown.  Here we present results from nine location-years of field trials over four seasons, investigating the effects of foliar B application on canola yield and yield components.  Foliar B application significantly increased yields in 1/3 of the trials.  Positive effects of foliar B were strongly associated with a shift in the total pod load and seed mass from the branches to the main raceme.  Numbers of viable pods on the branches were unaffected, but there were fewer aborted pod positions on the branches in the plots treated with B, indicating a reduction in flower initiation.  In one extremely high-yielding site (approximately 3 times the average yield of the other eight locations) where there was a much higher pod load, foliar B application significantly reduced yield.  We speculate that foliar B exerts its effect by causing the plant to prioritize flower positions that are setting pods when the B is applied, to the detriment of potential pod set at later flowering positions.  This reduces total flower number which may be beneficial under resources-limited conditions, but would be detrimental under ideal conditions when the crop could support a much higher pod load.