Effect of Long-Term Potassium Restriction on Nutrient Contents in Fruits and Leaves, Yield, and Potassium Deficiency Symptoms in Southern Highbush Blueberry

Potassium (K) is an essential nutrient for humans, but impaired kidney function requires dietary K restriction, increasing the demand for low-K crops. K is also essential for plants, playing important roles in osmotic regulation and enzyme activation. Most studies on low-K crop production have focused on vegetables, whereas research on fruit trees remains limited. In southern highbush blueberry (SHB), the greatest reported reduction in K content in the fruits is 53%, and the maximum K restriction period is five months. Therefore, this study investigated the effects of long-term K restriction on SHB after 17 and 29 months of treatment. Long-term K restriction reduced K content in the fruits by 72–83%, but also significantly decreased yield and induced severe K deficiency symptoms throughout the canopy. Decreases in K content in both fruits and leaves were accompanied by increases in sodium, calcium, and/or magnesium contents, depending on the organ. K content in the fruits reached approximately 20–30 mg·100 g−1 FW after 17 and 29 months of K restriction. These findings demonstrate that long-term K restriction effectively reduces K content in SHB fruits. However, further studies are required to optimize K management to maintain plant vigor and yield while enabling the production of low-K SHB fruits.