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Leaf Testing - Making the Soil Connections

Many fruit growers completed leaf analyses this past summer. And now when you get a moment, you may look over your reports and start scratching your head wondering why the report shows a potassium deficiency but your soil test indicates adequate potassium levels.

At times it can be difficult to make a clear connection between soil and tissue analyses. So it is important to remember that both are snapshots taken at the time of sampling. Leaf nutrient concentrations can change over a short period of time during the growing season due to soil, environmental and cultural factors. But soil nutrient levels, like potassium and phosphorus, don't change quite so quickly.

When reviewing your analyses, consider the following two points. First of all, soil and environmental conditions affect potassium uptake. Secondly, the potassium concentrations in the leaves and in the plant will change over the season.

Potassium moves to the root by diffusion; moving in the soil solution from higher concentrations to lower concentrations. Diffusion and uptake can be hampered by damaged roots, low soil temperature and moisture, poor aeration, and low clay and organic matter content.
Several studies, looking at in season leaf nutrient levels, have shown that potassium concentrations are higher prior to flowering; while after harvest, they are lower.

The interesting thing is this: even though foliar potassium concentrations increased with increasing soil applied potassium, the leaf levels still decreased between flowering and post-harvest. While the foliar potassium seems to indicate declining potassium levels, the overall plant potassium concentration increased.

So, the connection between soil and foliar testing may not always be clear at times, however used together, they can help you manage a perennial crop's nutrition