As yield expectations have soared in recent years, so has the importance of nutrient management.

Apple growers who were once happy harvesting 60 bins per acre are now counting on eventual annual yields of 100 bins or more to cover the high cost of new plantings.

“With increased crop loads, we have to replace a large amount of nutrients that are being taken out of the ground and the trees when we harvest those crops,” said Tim Welsh, horticulturist with Columbia Fruit Packers in Wenatchee, Washington.

Dave Gleason, horticulturist with Kershaw Fruit Company in Yakima, Washington, said growers have been shifting from focusing primarily on nitrogen fertilizers to using blends of nutrients that include potassium, phosphorus, and magnesium, and even minor elements.

“If your annual yields are up in the 80- to 100-bin range, definitely, the trees are mining a lot from the soil and you’re going to have to put something back in,” he said. “It’s been more common in row crops to do blends of fertilizer, but there are some people who are doing that in apples. A lot of people, when they establish these new blocks, are putting in drip systems and spoon-feeding the trees, watering two to three times a week instead of once every ten days. They’re able to meter things in small amounts exactly where the roots are.”

New approach

Harold Schell, horticulturist with Chelan Fruit Cooperative in north central Washington, agreed that it’s not just about nitrogen any more. A new approach to nutrition has been dictated by the modern, intensive growing systems that differ from those of the past.

Growers are producing different varieties, and the trees are on dwarfing rootstocks that are shallow rooted and more precocious.

“Because of that, nutrient management has gone to another level, because you’re having to manage a root zone that’s not as deep as it once was,” he said. “With irrigation, you can lose some of whatever you’re putting on the ground to augment the growth of the tree. A lot of things are coming into play that once weren’t nearly so important.”

Growers are micromanaging nutrients to get the maximum out of their trees—first of all to build the canopy as quickly as possible, and then to produce high yields of quality fruit.

But how does a grower figure out which nutrients need to be applied?

Schell said there’s a lot to be learned about the nutrition needs of the modern orchard, but little research available. Washington State University’s tree-fruit soil scientist Dr. Frank Peryea, who was based in Wenatchee, retired in 2008 and has not been replaced.

But Jake Gutzwiler, chair of the tree fruit industry’s Endowment Advisory Committee, said hiring a scientist to work on soil and nutrition issues is an industry priority. The committee will recommend that WSU create an endowed position in this area, using funds from the special assessment that tree fruit growers are paying for research at WSU. “That’s one of the top priorities,” he said. “It’s absolutely critical.”

More answers

Many growers hire commercial firms to do soil and leaf testing, but Schell, who is on the board of the Washington Tree Fruit Research Commission, would like to see  WSU soil scientists come up with data to help point the industry in the right direction.

“We’ve been striving to get more answers on what our soil problems are and some sort of way of knowing in different locations and different soils what exactly is needed for optimum growth and fruit production,” he said. “The benchmarks are not defined. Right now we can do a soil sample, or leaf sample, or whatever, and they give us some parameters to use, but not always is that a silver bullet.”

Ideally, when growers get tests results back, they would know what to do to achieve certain results, he said.

Mike Robinson, general manager at Double Diamond Fruit Company in Quincy, Washington, said there’s a substantial lack of good information on tree fruit nutrition. He’s had many tests done in orchards over the years but seen no correlation between the test results and the ­performance of the trees.

Robinson said good nutrition has always been important for the tree fruit industry, but when the stakes go up, everything becomes more important. “We’re just as confused as we used to be,” he said, “but there are more dollars involved.”

He is on a committee that has been formed to improve communication between WSU’s soil science department in Pullman and the tree fruit industry and to develop a road map for future research.

“We would really like to engage them in our interests,” Robinson said.

Welsh said he’d like to know what nutrients are ­harvested from the tree along with the crop.

“I would like to be able to measure all the nutrients that come off the tree,” he said. “Nitrogen, calcium, potassium, magnesium, all of those elements are so critical, and we’re mining them out of the trees when we harvest the fruit. Nitrogen is still significant, but much less ­significant than it used to be.”

Until someone has the answers, Columbia Fruit is having soil samples done by a private company and is changing the way it’s applying nutrients from just a nitrogen-based application to a holistic management system, Welsh said. The company is applying compost that it makes in-house. Waste from its packing operation is combined with other waste materials from a bean processor and dairies in the area.

“We’re still using synthetic fertilizers as well as compost,” he said. “I’m hoping it will help the soil biology, as most of the soils I’m growing on have been mined over the years and need revitalizing.”