Pop quiz answer

Today’s post is a follow-up to yesterday’s quiz on foliar fertilization.  I asked our blog readers to match the needle nitrogen content of Nordmann fir trees with the fertilizer treatments they had received.

Nutrient deficient Nordmann fir

The correct order is:

1)      control: no fertilizer 0.98%
2)      soil applied controlled release fertilizer 1.70%
3)      foliar nitrogen fertilizer 1.14%
4)      soil applied fertilizer + foliar feed 1.91%

While the foliar fert had a small effect, it’s important to note that, from a statistical standpoint, foliar fertilization did not significantly increase needle nitrogen concentration.  Moreover, foliar feeding alone was not sufficient to overcome the nitrogen deficiency of the control trees.  The main effect was from fertilizing the soil (actually container substrate is this case).

The take home message is that plants have evolved (or God designed them, if you prefer) to take up nutrients from the soil through their ROOTS.  They’ve been doing it for millions years and have been getting along quite nicely, thank you.  No matter how slick and clever the marketing, attempts to ‘short-circuit’ the process such as foliar feeding or trunk injection are short-term solutions at best or, as in this case, almost totally ineffective.  Foliar feeding and trunk injection treat symptoms, not causes.  Plant nutrient deficiencies occur because: 1) an element is lacking in the soil or 2) because the plant can’t absorb enough of the element (e.g., iron chlorosis).  Effectively dealing with a plant nutrient problem requires understanding which of those two situations is occurring and why.