Foliar Application of Boron and Zinc Influence the Vegetative and Reproductive Growth, Yield and Fruit Quality of Citrus Reticulata Blanco. Cv. Kinnow

Among the micronutrients, B and Zn play very vital role in the nutrition of citrus. To study the influence of foliar application of boron and zinc (as boric acid and zinc sulphate) on the tree growth and fruit quality of Citrus reticulate Blanco cv. ‘Kinnnow’, two separate experiments were conducted. In the first experiment, boric acid at the rate of 0, 0.1%, 0.2%, 0.3% and 0.4%, and in the second experiment, zinc sulphate at the rate of 0, 0.2%, 0.4%, 0.6% and 0.8% were sprayed after fruit setting stage to the nine year old Kinnow mandarin trees budded on Rough Lemon (Citrus jambheri L.) root stock. Foliar application of boric acid (0.3%) significantly increased the leaf N, P, Ca and Mn levels, while leaf K and Zn levels were highest with 0.2% boric acid application as compared to other treatments. The trees sprayed with 0.4% boric acid showed highest leaf B contents in Kinnow mandarin leaves. Tree height and flush length; fruit yield; fruit titratable acidity, ascorbic acid, total sugars and non-reducing sugars were highest when trees were sprayed with 0.3% boric acid in contrast to other treatments. In the second experiment, foliar application of 0.2% zinc sulphate showed highest increase in N and Ca levels in Kinnow mandarin leaves, while trees sprayed with 0.6% and 0.8% zinc sulphate exhibited higher level of P and K respectively. Maximum leaf Zn, Fe and Mn concentrations were observed in trees sprayed with 0.8%, 0.6% and 0.2% zinc sulphate in the Kinnow mandarin leaves respectively as compared to other treatments. Tree height and tree spread was significantly increased with 0.6% zinc sulphate sprays, whilst lowest fruit drop and highest yield was obtained from trees treated with 0.4% zinc sulphate as compared to control. Similarly, foliar application of zinc sulphate also improved the fruit quality in terms of total soluble solids, total sugars, ascorbic acid contents than untreated trees. In conclusion, foliar applications of B and Zn can be used effectively to improve the leaf mineral status, yield and fruit quality of Kinnow mandarin.