Page 17 - Griffin Gazette Q3 2017
P. 17

By Tami Van Gaal, CEA Division Leader

A solution for low-alkalinity water
Imagine this scenario: The pH of your fertilizer solution needs to be adjusted down with
acid to reach your target pH. All is going well for a period of time until the pH suddenly
drops rapidly and doesn’t seem to hold in the manner you expect. What happened?
One possibility is that the continuous injection of acid eroded the alkalinity of the water.
Alkalinity is a natural buffer. Waters lacking buffering capacity can experience rapid pH
changes in response to the addition of acid or basic materials, including fertilizers.

Imagine a second scenario: You are a grower in a warehouse production space that
uses reverse osmosis (RO) water. The RO process strips all of the alkalinity, or buffering
capacity, from the water. Any addition of a non-neutral fertilizer or supplements will result
in a change that must be compensated. Even when fertilizer programs are well balanced,
the pH of these solutions must be closely monitored.

Fortunately, there's an easy, crop-friendly way to add buffering capacity back into the
water: potassium bicarbonate. Griffin’s GGSPro team recommends adding potassium
bicarbonate to your fertility program whenever your clear irrigation water has less than 50
ppm CaCO3. Potassium bicarbonate will also provide a touch of potassium to the crop,
which is generally a favorable addition and easily managed in the greater fertility program.
With improved buffering capacity, you can work to build a great fertility program for your
crop that is also forgiving; remember to ask GGSPro for help in this process.

If you are using concentrated stock tanks, remember that potassium bicarbonate is a
product that needs to be injected solo; avoid mixing potassium carbonate with other
fertilizers and supplements in concentrated form.

Which crop likes air flow directed onto the plants?
Properly placed HAF fans will move the air around a crop without actually blowing air onto
a crop. With few exceptions, directing fans onto crops is avoided. While a little airflow is
a good thing, turbulent air flow over a crop resulting in visible movement of the crop can
have a detrimental impact on crop growth. When air flow over a leaf surface is high, the
stomates close to reduce transpiration and prevent excessive moisture loss. Stomatal
closure reduces carbon dioxide availability to the crop, which reduces photosynthesis
and growth. This is generally very evident in production – plants in the direct path of
airflow are generally shorter and have less vegetative growth.

There is one crop for which a more direct, vertical air flow onto the crop is beneficial.
Under low light and higher humidity, lettuce crops can develop tip burn of the interior
leaves. This tip burn is also known to occur under excessively high DLI in lettuce – greater
than 12 mol/m2/day without good air flow and 17 mol/m2/day with good air flow. Tip
burn of the young leaves is often caused by a calcium deficiency due to low transpiration
resulting from pockets of stagnant air at the growing tip. Gentle air flow in a downward
direction over the crop has been shown to improve transpiration of the young leaves and
reduce the incidence of tip burn. The key is “gentle air flow.” It doesn’t take a lot of air
flow to improve transpiration. No gale-force winds are needed! Instead, achieve gentle air
flow with vertical air flow fans. These large paddle fans, mounted above the crop, have
been shown to produce enough downward air movement to improve transpiration at the
growing tips and reduce the incidence of tip burn.

Photo Caption: Calcium deficiency, showing as the brown, marginal burn on these lettuce
leaves, can be minimized with proper air flow over the crop.

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