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A New Look at Potassium

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Almond trees that normally do not need potassium but which have started showing signs they could now be deficient of the nutrition may not be such a surprise, according to Extension soil specialist Roland Meyer.

As a result of a new emphasis on potassium in some almond plantings, Meyer is conducting new research to help producers use the right material properly.

"Trees that did just fine on normal planting spacings before they started getting bigger yields may not have needed much potassium, but now that has changed in many orchards," he said during Nickels Field Day in Arbuckle.

As a result, it is time for growers to take a hard look at what their almond potassium needs may be today, he advises.

"Increases in yields have placed more demand on trees along the western side of the Sacramento Valley," he explained. Improved irrigation and closer plantings in almond orchards have done much to enhance the yield level, playing a role in the new focus on potassium in the area.

That means producers in the district may join their almond neighbors on the east side of the valley in the necessity to add potassium. The nutrient has been a common ingredient of the fertilizer program on the east slope for years, noted Meyer.

"Some growers who normally do not see potassium shortages are beginning to notice problems in leaf samples," he said, "and wondering why this suddenly has happened."

"High yielding almond orchards with declining leaf potassium levels (the critical range is 1-1.2 percent in July samples) on western Sacramento Valley almond orchards_and other areas of the state_have given growers cause for concern over how best to apply potassium," Meyer told the annual field day crowd.

He hopes new research at the lab here will provide some important answers in 1996.

As yields continue to climb, boosting their need for potassium, they eventually reach a point at which the very lack of the nutrient will restrict further increases, pointed out Meyer. "The tree yield is limited by the most limited nutrient," he said, "and potassium (shortages) could be the biggest of these problems today for some."

But how do growers unaccustomed to using potassium put the material on? Most apply bands of fertilizer three to four feet from the tree, hoping water will run the material into the ground and reach roots.

"The irrigation of almonds is accomplished with a number of different systems," said Meyer, "that may apply the necessary water to a very limited soil volume or wetted area, up to flooding the entire soil surface and wetting all the soil."

Some irrigation systems may take the material down, but in various situations such as low volume, the material may face a dry below-ground situation once it absorbs into the soil, said Meyer, lessening chances for the material to become available.

"Drip and microsprinkers may be more efficient in many respects, but we want to look at how effective they are in application of potassium, and what role injected material may play in almond nutrition," he said. Many growers like to band the product, he noted, since it is the easiest way to apply.

Fertilizers may be applied to the soil surface in a band or broadcast before irrigation, he said, or put on prior to winter reins or through the irrigation to help it move the materials into the soil.

"If added through a low volume or smaller wetted area system, even potassium fertilizers which are not easily moved in soils have been taken up readily by trees," he reported.

But some fertilizers are not dissolved easily, he said, or water quality characteristics prohibit trouble-free injection. "Growers may choose to use application on the soil surface as an alternative,"," he noted.

"The availability of several new potassium formulations and traditional sources of potassium sulfate, phosphate, nitrate and thiosulfate make it easier to inject into irrigation systems," he said.

"Given the different types of application now being utilized, it seems prudent to evaluate the relative efficiency of potassium uptake from several sources and methods of placement," said Meyer. In fact, just such a study is already under way at the Marine Avenue location in the Nickels Soil Lab, he announced.

Objectives of the probe will include evaluation of the effects of different placements, sources, and rates of applied potassium on growth; a look at the nutrient concentrations in leaves and nut yields of almonds; and assessment of the extent of potassium movement in the soil under these regimes, he explained.

What is interesting to a lot of the industry today is the new so-called "solutionized" form of potassium available for the first time in 1996.

"I know that there is no panacea in potassium application or materials for almonds. but it is important that we look at what is available and try to decide which way is best to go," said Meyer.

Some materials such as potassium chloride must be "watched very closely" he said, advising growers to take leaf samples through harvest. Tip and margin bum, he warned, can develop unless caution is used with this formulation.

One of the problems facing researchers with almond potassium is that while it is common knowledge that leaf tissue analysis does reveal an increase in the nutrient, "we have not been able to relate this to a yield increase as of yet," said Meyer, who predicts that the response of the tree yield to potassium will "probably not be as notable as the response we see when using nitrogen."

Another criteria the grower must consider is whether applying potassium at, for example, 400 pounds an acre is worthwhile in terms of returns. If almonds are $1 a pound, the applications may pencil out, illustrated Meyer, but at a lower price, adding potassium may not be economically efficient.

Among the warnings Meyer issues is to avoid the chelate sell. While some may advertise such a product "there in reality is no such thing as a potassium chelate," he said, "or if it exists, it would be a very weak product."

Meyer urged growers to avoid falling prey to those who claim chelated potassium is a very effective material.

As new almond growers enter into potassium use, their best bet may be :to contact experts like Meyer and follow the results of his research at Nickles Estate where Butte and Nonpareil rows of almonds will be included in the trial.

The test orchard was planted in spring of 1990 to Butte, Carmel, Nonpareil and Monterey almonds with trees spaced on a 16 by 22-foot diamond of 145 trees per acre. Individual test plots will be of five trees each.

Already tree circumference measurements have been recorded for each tree in the selected plots, said Meyer.

Treatments will be conducted under drip irrigation on single line, double line drip and with microsprinklers on 7 2 plots.

"Potassium sources will include potassium sulfate, monopotassium phosphate, potassium nitrate and potassium thiosulfate," he explained. Several rates will be injected via the irrigation systems to compare to higher rates applied to soil surfaces in bands three feet from trees on both sides of the row_the normal fall practice used in almonds today.

"Injection treatments began this spring and will continue throughout the growing season," he said. "Leaf samples will be taken to evaluate nutrient uptake and yield data will be collected to determine treatment effects."

Soil samples will also be examined at the end of the season to evaluate potassium and phosphorus movement, he added.

With all this under way at Nickels , it appears those new questions being asked about phosphorus on almonds on the west side of the Sacramento Valley will see some solid answers at next year's Nickels Field Day, if not sooner.