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.”
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.”