Potassium Is Important In Almonds

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Staying vigilant to maintaining almond orchard nutrition is the best way growers can avoid eventual depletion of important nutrients like potassium (K), which plays a major role in many plant processes, says David Doll, a pomology farm adviser for University of California-Davis (UC-Davis) in Merced County, CA.

“Potassium promotes root growth, increases kernel and fruit size, and provides key metabolic features including the formation of starch, translocation of sugars, stomata regulation, and the formation of xylem vessels,” Doll says.

Removing almond hulls and kernels during harvest also removes significant amounts of potassium from almond orchards, but depletion can be avoided by regularly applying potassium to the soil.

“Tissue analysis has shown that almond hulls and kernels are about 3% and 1% potassium, respectively, so for every 1,000 pounds of kernel meats harvested, about 50 pounds of potassium are removed,” Doll says. “Soil application of potassium is the most effective way to deliver potassium to the tree. Ensuring that the amount of potassium removed from the orchard is replaced will help maintain high yields.”

Potassium-Rich Products

Conventional Applications:
Sulfate of potash
Muriate of potash
Potassium nitrate
Potassium thiosulfate (K-T-S)

Organic Applications:
Manure composts
Green manures
Guano
Wood ash

Growers can ensure that they keep their almond orchards in top health through proper fertilization of their trees, according to Doll.

“A balanced fertility program is critical to maintaining a healthy orchard, environment, and wallet,” he says. “Since potassium reacts differently than nitrogen in the soil, applications need to be placed in the right amounts at the right place at the right time. Potassium should be applied annually to rebuild levels; and even though tissue and soil analysis can be expensive, it can quickly pay for itself by preventing a deficiency.”

Leaf Sampling And Fertilization

Plants that are potassium-deficient grow slower and have small, pale leaves, and trees that are severely deficient may have necrotic tips and margins. In many cases the leaf tip curls upwards in a common symptom named Viking’s Prow, according to Doll. Foliar fertilizer applications can be used to address an in-season problem, but are not adequate to address long-term potassium deficiency, he says.

“I try to get growers to think of foliar sprays like a crutch,” he says. “Foliar sprays are often noted to perk the tree up, and they do, but this effect is relatively short-lived if the tree is deficient in vital nutrients. Within almonds, it would be very expensive to apply the annual potassium needs of a tree through foliar nutrient applications, considering a 3,000-pound crop requires the application of at least 150 pounds of K. The biggest bang for your buck comes from soil applications.”

While depletion of soil potassium doesn’t happen overnight, or even over just one season, long-term effects of potassium deficiency will cause yield loss, Doll says.

“Reduced crop load, loss of fruiting wood or spurs, and poor tree growth are all caused by long-term potassium deficiency,” he says. “Usually yield loss is gradual and once the trees show signs of deficiency, yield has already been lost.”

This is why regular potassium leaf and soil sampling are so critical to maintain healthy almond orchards, Doll stresses.

“Annual mid-July leaf sampling from non-fruiting spurs will allow growers to compare leaf potassium levels with UC standard guidelines,” he says. “Leaf K levels should range from 1.4% to 1.8%. Leaves are deficient if potassium levels are below 1.4% and no growth benefit has been observed with leaf potassium levels higher than 1.8%.”

Growers must remember that potassium levels will be lower in fruiting spurs and in leaves at the top of the tree, which is why growers see a positive effect of leaf K levels higher than 1.4%, Doll says. “In other words, just because the leaves you sampled are at 1.4% doesn’t mean the leaves at the top of the tree or fruiting spurs are at 1.4%; they are usually lower, therefore deficient and negatively impacted for the coming year.”

Performing soil analysis tests every three years will allow growers to track soil potassium levels. Potassium within the soil will gradually drop with every crop load if no potassium fertilizer is added, and once it drops, it will take several years of large applications to bring the levels back to normal. Continued monitoring and fertilization will help growers build soil potassium levels, according to Doll.

“Since potassium binds easily with soil exchange sites, it does not move readily in the soil; therefore, potassium must be delivered as closely as possible to the root system,” he says. “Placing a band of fertilizer within the irrigation wetting zone will help move the fertilizer into the soil. Dormant season applications can also be made. Since potassium does not leach from the soil profile like nitrogen, winter rains can move the nutrient into the rooting zone.”

Laura Drotleff is managing editor of Greenhouse Grower and Today's Garden Center.

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