I have often observed potassium deficiency in young vigorous second-generation orchards. In many of these cases the first-generation orchard probably had plenty of potassium stored in the soil and the grower didn‘t observe deficiency symptoms and didn‘t apply potassium. But that first-generation orchard probably used up most of the available potassium in the soil, and when the second-generation orchard is planted potassium is limited. Then potassium deficiency symptoms can become visible in young second-generation orchards and growers may end up applying as much potassium as nitrogen.

Young, vigorous growing orchards often display symptoms in late spring to early summer on leaves of new shoots. Leaves can turn pale and develop marginal necrosis and roll into a boat shape or the classic ‘Viking‘s prow’ symptom. The ‘Viking‘s prow’ symptom typically shows first in the tops of trees and later throughout the whole tree. As potassium deficiency progresses, fruit bearing spurs often die and spur renewal is reduced.

The current crop is not affected but future yields are reduced, making the correlation between potassium deficiency symptoms and reduced yields difficult in a single year. Butte is a good indicator variety of potassium deficiency, displaying symptoms while other varieties do not. Recovery from potassium deficiency is a long-term process, once you see leaf symptoms the trees are already deficient and you may experience yield loss before you can correct the problem. Leaf analysis should be performed annually in July to prevent symptom development.

The current UC recommendation is to keep leaf potassium levels at or above 1.4 percent in July-sampled leaves.

An almond tree in production uses as much potassium as nitrogen, and similar to nitrogen, 10 pounds of potassium are needed for every 100 pounds of nutmeats. Thus, a 2,000-pound per acre crop will need approximately 200 pounds of potassium to replace the potassium that was removed in the crop. Potassium is released slowly in the soil and not readily leached.

Because the potassium ion (K+) is positively charged it can easily be bound with negatively charged clay particles and become unavailable to the tree. For this reason, we typically apply potassium sulfate in bands next to the tree rather than broadcasting. Potassium sulfate is preferred over potassium chloride because of salt accumulation in the soil. UC research has demonstrated that annual fall applications of 500 pounds per acre of banded potassium sulfate would maintain potassium levels.

Two thousand pounds per acre of potassium sulfate can correct a deficiency for four or more years — but it‘s expensive. In clay soils double-concentrated bands may be necessary. You may also wish to apply gypsum, calcium sulfate, as a band over the top of previous potassium bands. The calcium ions (Ca++) will displace potassium bound to clay particles, making more potassium available while also improving water penetration.

Liquid potassium fertilizers can be applied effectively in-season through your irrigation system, and drip systems are probably better for potassium applications than micro-sprinkler because the amount of K+ per wetted area is higher, and as a result, potassium will penetrate further into the root zone and be more available. But liquid potassium is generally more expensive and you may not apply as much potassium per acre compared to banding potassium sulfate. Avoid applications that spread potassium applications over a large soil area because it will become bound to the soil and unavailable to the tree. Foliar in-season potassium sprays can alleviate symptoms more quickly, but are relatively expensive and their effect is short lived.