N’Synchronicity Pays

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Strawberry Stewardship

There’s an old saying that nothing breeds success like success. But that can be taken too far. Tim Hartz, a University of California (UC) Cooperative Extension specialist, says that growers can become too complacent. For example, Hartz, who works in the Department of Vegetable Crops at UC-Davis, says many of the state’s strawberry growers put down a standard NPK (Nitrogen, Phosphorous, and Potassium) fertilizer without giving it too much thought.

“A lot of guys say ‘That’s what my dad used, and it worked great.’ Fine, all I’m saying is think it through, do the testing, and determine what you really need,” he says. “Have a soil test done and think about what that site requires, not what you’ve done historically.”

‘P’ Is For Plenty
Another impact of many years of NPK fertilizer applications in the valleys of California and many other longtime strawberry-growing regions is that there is an abundance of phosphorous (P) and potassium (K) in the soil. Mark Bolda, a University of California Cooperative Extension farm advisor in Santa Cruz County who specializes in strawberries and caneberries, says when doing testing for nitrogen (N), growers would be wise to pay careful attention to their P and K levels, as well.
“There’s often lots of potassium, but there’s especially plenty of phosphorous — massive amounts,” he says. “P is not mobile in soil like N. As does K, it just stays there.”
Bolda says that in the soil tests they’ve run as part of strawberry nutrient management project, they’ve found extreme levels of P, often on the order of 10 times as much as needed by the plants. There’s really no mystery as to why the levels are so high. “We’ve been adding to that for how many years? How many years has California been farmed — 120 years? The phosphorous is high from building up over time,” he says. “It doesn’t move on its own, like N.”
Bolda recommends that strawberry growers run a trial on a portion of their ground. It’s a good way to really tell what the effects will be without jeopardizing all their crop. “Say you have 100 acres,” he says. “Take 10 acres, put less phosphorous on this season and see what happens. Look at the effects on the plants, and at the same time check those nutrient levels.”
If the grower farms in California or any ground that’s been in strawberries or certain other vegetables for a long time, he’s pretty sure the grower will benefit from backing off on P applications. “Some people are deficient in phosphorous, such as people farming in an area that’s only been farmed for 10 years,” he says. “They might not have enough P or K, but not here.”

Hartz makes the recommendation based on a series of nutrient trials conducted in 2010 in the heavy strawberry production areas of the state’s central coast. A team of researchers surveyed 26 fields in the Watsonville-Salinas and Santa Maria areas to revise tissue sampling nutrient standards on the Albion strawberry variety. In addition, they monitored the irrigation and fertility practices in 14 additional fields in the Watsonville-Salinas area. The results were clear. Many growers were wasting too much preplant fertilizer.

“If you’re using a preplant, the minute you put it down in the moist bed it will start to release, but it’s not being used,” he says. “We’re seeing too much fertilizer being released when the crop can’t use it, especially like last year when we had a wet winter. The crop uptake doesn’t start in earnest until February or March, but you applied it several months earlier.”

Times Have Changed
Some factors have changed since today’s growers’ dads were in charge, says Hartz. For example, it used to be that everyone fumigated with methyl bromide, and you didn’t have to build your beds so early. In addition, he speculates that older fertilizers may have been developed in warmer areas such as southern California, where fruit is present in January. In those warmer climates, you want the nutrients available in January.

What growers need to keep in mind is that strawberries are incredibly predictable when it comes to nutrient uptake. They take up 1 pound of N per day, per acre when they begin to really get going, which is in later February or early March in the coastal areas of central California. The researchers ran those calculations in eight or nine fields, and that number stayed amazingly consistent, ranging from a low of 0.9 pounds per acre per day to a high of 1.2.

Growers should adjust their fertilizer amounts and times accordingly. If well water is high in nitrates, adjust for that. Or if the soil is rich in organic matter, account for that. Just make sure there is a minimum of 1 pound per acre per day available. “There shouldn’t be a need for large dollops of fertilizer because that need is relatively modest and quite consistent,” says Hartz.

It’s a far cry from vegetable crops such as lettuce. When lettuce first starts getting going, it needs almost no N. But then it hits a certain point, and for a month it will take up 3 to 4 pounds per acre per day. “The berry is more like the tortoise,” says Hartz, “the vegetable is more like the hare.”

 

 
David Eddy is editor of American/Western Fruit Grower, a Meister Media Worldwide publication.

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