Foliar application of potassium nitrate increased individual fruit size in citrus trees.

The paper describes the effects of a single high concentration spray of potassium nitrate enriched with soluble N-P-K phosphate (13-2-44) and a special adjuvant on citrus yields, fruit quality and grower profitability. All experiments were conducted in a mature citrus orchard (over 15 years old) in central Israel.

Foliar nutrition with this potassium nitrate enriched product achieved the following results in citrus crops:

• In 'Shamouti' ("Jaffa") oranges, a single application of 9-10% (w/v), when fruits were 18-22 mm in diameter, increased the percentage of fruit size above 75 mm (diameter) by 75%, consequently, total yield increased by 14 ton/ha. Postharvest shelf life was also significantly improved due to a marked increase in the potassium content of the peel by 0.44% (dry basis).
• In navel orange 'Newhol'(Citrus sinensis Osb.), a single application of a 10% solution, when fruits were 15-20 mm in diameter, significantly increased total yield by 19% and fruit sharing a diameter over 75 mm increased by 28% (Figure 1).
• In Nova mandarin (Citrus reticulata Bla.), a single application of a 10% solution, when fruits were 12-20 mm in diameter, significantly increased total yield by 30%, average fruit weight by 38.3 g and reduced the incidence of peel enlargement by 20%.

The described experiments showed that foliar application of potassium nitrate is recommended for high yield and fruit quality in citrus.  The applications resulted in agronomic and economic benefits compared to the non-spray control in terms of leaf nutrient content, fruit peel, total yield, fruit size distribution, and grower inputs. The shift toward larger fruit size distribution is the major factor in producing higher inputs because higher market prices are received for larger fruit.

Effect of foliar application of potassium nitrate enriched with soluble phosphate and a special adjuvant on the size distribution of 'Newhol' navel orange.