Mobility within tree: High (symptoms in older leaves first)

Uptake Form: K+

Function: water and energy, link to improve cold hardiness

Deficiency/Toxicity Symptoms:  Potassium deficiency is not a common disorder in British Columbia.  It is characterized by reddish brown leaf scorch and chlorosis.  Potassium deficiency has been shown to be more common in high density fertigated orchards, especially when drip irrigated (Sallato et al. 2019). The deficiencies usually develop in sandy, coarse textured soils and show up as trees begin heavy fruit production usually in the third year. Symptoms of increased susceptibility to winter injury and spring frosts may appear when leaf potassium is below 0.70%.  Potassium deficiency is less common in lower density orchards with sprinkler irrigation, but has been reported when soil potassium levels are low.  Some studies have shown an improvement of fruit colour when potassium nutrition moves from deficient to adequate levels.

The symptoms of excess potassium are unknown.  Unnecessary application of potassium to tree fruits may interfere with uptake of calcium (Ca) and magnesium (Mg).  Calcium is especially important for the prevention of bitter pit and breakdown in apples and preventing Anjou pit in pears.  Magnesium is important in preventing leaf scorch and premature dropping in apples.

Potassium Sources

Common sources of K fertilizers used for fruit trees in BC is presented in Table 1.

Table 1. Common available K fertilizers in B.C.

Potassium Application

For broadcast K applications, apply 200 kg K/ha when soil and leaf K levels are low.  The rates can commence in the first year and then be adjusted upwards or downwards depending on K concentration in subsequent years.  Nitrogen-K fertigation should be considered for high density orchards on sandy soil especially when drip irrigated.  It is also important to monitor leaf Mg and fruit Ca to avoid any negative antagonism with K. Recommended fertigation rates for tree fruits is presented in Table 2.  

Table 2. Possible K fertigation rates for fruit trees

*If planting is high density reduce the amount of K₂O/tree so that 50 kg/ha or 20 kg/acre is not exceeded.

**It is also important to monitor leaf Mg and fruit Ca to avoid any negative antagonism with K.