May 3, 2021 4:10 pm Published by Donna

Blink twice and it’s May: 2021 is already passing at speed. But it’s not too late for some nutrition planning to maintain yield potential across all kinds of tree fruit, says agronomist Francisco Rivera of California-based OMEX® Agrifluids.

“You never know how a year’s going to turn out,” says Francisco, “but that uncertainty doesn’t mean you can’t plan ahead as far as nutrition is concerned. If you’ve made sure to give the tree all it could possibly need in terms of essential nutrients and elements, then you’re priming it to deliver the best possible yields.

“If you don’t give a tree the best, it can’t deliver its best,” he warns.

“Fruit of all kinds is packed with nutrients, vitamins and minerals of all kinds. That composition

demands a lot of nutrients from the tree. And when there’s a particularly good crop, nutrient levels in the tree can fall dangerously low.”

Francisco says it’s essential that growers take steps to raise these nutrient levels before the tree needs them again. “Nitrogen for vegetative growth and bud formation; potassium for growth, water optimization and fruit development; and calcium for high quality, disease-free fruits.”

But of the three nutrients in question, calcium is one to watch. “Very early in the season, even after a heavy harvest the previous year, trees will continue to take nitrogen and potassium from reserves, at least until top-up treatments can be applied ahead of key events such as fruit set and during development.

Rule #1

“Calcium is different. The first golden rule to remember is that crops cannot store excess calcium.”

Unlike potassium and many other nutrients, Francisco explains, plants have no capacity to store reserves of calcium. In fact, once they’ve topped-up their calcium storage — in the calmodulin proteins between the cell wall and cell membrane — any excess calcium is ejected through the leaves, even if fruit is displaying calcium deficiencies.

“This also sheds light on why tissue testing for calcium is so unreliable,” warns Francisco. “Not only is there no connection between leaf tissue calcium and fruit tissue calcium, but the difference between acceptable levels and deficiency can be as small as 2ppm — outside any analytical tolerances.”

Rule #2

The second golden rule is that calcium can only move up. “Plants can’t move it from one place to another,” says Francisco, “because it’s not phloem mobile. Instead, it moves through the xylem, following water through the tree from the roots to the places of highest water loss — usually the top-most leaves.

“This explains why any water-related conditions — drought, waterlogging, wind — can bring about calcium-related quality problems such as bitter pit in apples.”

Rule #3

Finally, calcium transport into cells is directly influenced by the plant hormone auxin. If there’s no auxin present, then crops won’t absorb calcium properly, irrespective of how much is applied.

“Auxin is involved in cell division,” explains Francisco. “New tissue — as found in developing fruit — has high auxin levels and can absorb good levels of calcium. But once the fruit has all its cells and shifts to cell expansion — maturation — its ability to absorb calcium decreases rapidly.

“Young fruits absorb calcium well; maturing fruit will struggle.”

Understanding this aspect of the tree’s physiology was crucial in helping a British agri-tech company, Levity Crop Science, create the science needed to support better calcium nutrition. Its research team came up with two technologies, LimiN® and LoCal®, to circumvent the problem. Both are available in the U.S. through a unique partnership between OMEX® and Levity.

“This technology is like nothing else in the market,” enthuses Francisco. “When we evaluated the Levity tech as an additive to our own products, we couldn’t wait to incorporate them and bring their benefits to our customers here.

“We incorporated the LimiN® technology within Cell Power® SizeN®, co-formulated with calcium,” he continues. “LimiN® comprises a stabilized amine nitrogen, which emphasizes root growth and a good compact habit, characteristics required for a tree’s ability to supply calcium to the developing fruit.”

When trees receive standard nitrogen, reduced root growth and focus on apical shoot growth can create a huge calcium sink at the top of the tree, diverting calcium from blooms and fruit.

The second technology, LoCal®, uses a naturally occurring compound to mimic the effect of auxin, allowing plants to properly absorb calcium where they would normally have a low ability to do so. “Cell Power Calcium Gold and Cell Power Calcium Platinum both use LoCal® technology to supply fruit with calcium very effectively, ensuring good fruit set and improving tolerance to disease,” says Francisco.

For apples and pears, he recommends growers start with Cell Power® SizeN® K, with four applications of two quarts, applied through drip regularly through the season. This will allow a reduction in nitrogen applied from other sources, while increasing fruit load and size. In addition, Cell Power® Calcium Gold or Calcium Platinum — up to five applications at two quarts per acre, starting at flowering — will dramatically reduce incidence of bitter pit and russeting.

Cherries and other stone fruit will benefit from up to four applications of Cell Power® SizeN® at two quarts per acre: it will keep roots alive, maintain a good shape and maximize fruit load. Meanwhile, applications of Cell Power® Calcium Gold and Cell Power® Calcium Platinum are best started at flowering.

“Apply at 1 pint/acre, then top up after two weeks with a final one ahead of harvest. This will reduce cracking and increase yield.”

Learn more at

The product names and brands referenced here are registered and trademarks of OMEX® Agrifluids, Inc.

© OMEX® Agrifluids, Inc. 2021.

Calcium: Three Golden Rules for the Tree Fruit Grower


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