Effects of potassium chloride application on chloride accumulation in soil-navel orange trees and leaf nutrition and fruit quality

Objectives  The effects of potassium chloride on leaf nutrition, fruit yield and quality of navel orange, and chloride accumulation in the plants and soil were investigated.

Methods Field experiments were conducted in two orchards–acidic (pH 5.78) and alkaline soils (pH 7.44), respectively in 2018 and 2019. The test trees were 9-year-old of ‘Newhall’ navel orange ( Citrus sinensis Osbeck). The annual KCl application rate for each orange tree was 250 g (T1), 500 g (T2) and 1000 g (T3), taking K₂SO₄ rate of 556 g as control (CK). The leaf tissue contents of N, P, K, Ca, Mg, and Cl of spring and autumn shoots, peel and pulp of fruit were determined, the fruit yield and quality were evaluated, and the Cl^– contents in 0–20 cm and 20–40 cm depths of soil were assessed.

Results Application of KCl significantly increased Cl^– contents in soil and leaves. The Cl^– content in acidic soils was 50.20% higher than CK under T1 treatment, and 79.70% higher than CK under T3 treatment. In alkaline soils, it was 28.02% higher than CK under T1 treatment, and 99.36% higher than CK under T3 treatment. 2) The contents of N and Ca in leaves had no significant changes after the application of KCl, the K and P contents increased with the increase of KCl rate, while the Mg content varied under T3 treatment. Compared with CK, the Cl^– content of leaves in spring and autumn shoots in acidic soils increased by 21.9% and 8.0% in T1 treatment, by 51.9% and 45.0% in T2 treatment and by 63.8% and 58.0% in T3 treatment, respectively. In alkaline soils, it increased by 25.5% and 12.7% in T1 treatment, by 33.3% and 19.3% in T2 treatment and by 109.7% and 98.7% in T3 treatment, respectively. 3) The application of KCl had no significant effect on fruit yield, single fruit weight, rind brightness, rind yellowness, soluble solids and titratable acid contents. The redness of some fruits increased significantly after the application of potassium chloride instead of potassium, and the content of vitamin C increased with increase in KCl concentration.

Conclusions Short-term application of potassium chloride does not influence the Cl^– content in the fruits, although increases the Cl^– contents significantly in leaves and soils, but not beyond the safety threshold, regardless of orchard soil pH. Short-term potassium chloride application does not adversely affect fruit yield and quality. Therefore, potassium chloride is recommended for navel orange orchard production.