It’s for good reason that we attach importance to the role of potassium in plant nutrition — and fruit in particular, says Dean Konieczka, consultant agronomist with OMEX® Agrifluids USA.
Did you know that potassium is responsible for, or plays a part in, more than 60 different biochemical pathways within the plant? Vital for photosynthesis, essential for protein synthesis, it also has major function in regulating the opening of leaf stomata — the site of plants’ respiratory and water regulation.
Intricately associated with the movement of water, nutrients and carbohydrates — the products of photosynthesis, plants also rely on potassium for enzyme activation. In particular, potassium affects production levels of a key compound called adenosine triphosphate (ATP). ATP is instrumental in the regulation of photosynthesis.
It’s no surprise then, that when potassium supplies are challenged, plants respond: reduced yields, poor quality produce and greater susceptibility to damage from pests or diseases.
In fruit production especially, potassium is crucial in increasing the levels of vitamin C and sugar, improving their flavor and color, and encouraging growth — resulting in large fruits. And it’s not just while the fruit is on the plant that potassium has an effect: high levels also improve shelf life, by boosting the fruit’s resistance to damage from handling and transport.
But it doesn’t stop there. Potassium also increases drought resistance, through improved root growth and structure, a major consideration as we begin to experience more unpredictable patterns in weather, and farmers come under increased pressure to improve water-use efficiency.
So what’s the best way to ensure your fruit crop gets a healthy dose of potassium? While there’s often plenty of potassium naturally occurring in soils, not all of it is readily available to the plant — that is to say, in a soluble form.
In fact, in most soils, somewhere between 90 and 98% of the naturally occurring potassium is unavailable to the plant. For example, while mineral soils rich in feldspar and mica technically sport high potassium content, plants can’t access this crystalline form. Other soil processes will eventually break down these mineral forms into plant-accessible potassium, but it’s slow — happening over tens of years and unable to meet the season-long demands of a growing crop.
What’s more, a number of additional factors also influence a crop’s ability to absorb potassium. Chief among these is soil moisture. Potassium availability is linked to increased soil moisture, as this makes potassium more mobile. Research has confirmed that crops display more response to potassium fertilization during a dry year.
As well as soil moisture, soil aeration is also key — but here a happy balance needs to be struck. Roots need air for respiration, but as soil moisture increases then soil aeration decreases. In completely saturated soils, oxygen levels will be very low — with the decrease in root respiration also depressing potassium uptake.
Unsurprisingly, temperature is also a key factor. Optimum soil temperature for potassium uptake is between 60-80°F.
While not directly relevant to fruit crops, it’s also known that the tillage system can influence potassium uptake, with min-till systems seeing reductions in soil potassium availability. Although fruit growers can do little to change this, it’s interesting to note that results of research to identify possible causes for this point to restrictions in root growth. Growers may consider this as a factor in well-established, multi-season crops where soil is not regularly disturbed — these could be crops that are in need of some potassium assistance.
Potassium deficiency, if it’s spotted, usually manifests itself in older leaves first: they’ll appear light green and yellow, before turning to leaf scorch. At later stages in the season, small or misshapen fruit may be an indication too.
It’s in these sorts of circumstances where growers might turn to a foliar potassium fertilizer. Foliar products offer a faster uptake than soil-applied products; not only does this give growers the chance to correct any deficiency more quickly, but it also improves use efficiency — the plant can access a greater proportion of what’s been applied.
OMEX® CELL POWER® K25 has been developed to offer growers not just soluble potassium, but also an important supplement of the plant hormone cytokinin. Vital for good root systems, its addition in K25 helps to manage and eliminate the plant stress that can occur as fruit load develops later in the season.
Using K25 from late bloom and early fruit set allows growers to produce quality produce from first set all the way through to the final set.
Learn more at www.OMEXusa.com.
The product names and brands referenced here are registered and trademarks of OMEX® Agrifluids, Inc.
© OMEX® Agrifluids, Inc. 2021.