Zinc Nutrition in 'Nagpur' Mandarin on Haplustert

Zinc (Zn) deficiency is the most prevalent nutritional disorder in citrus orchards world over. The management strategy of Zn deficiency today is still governed by the efficacy of two conventionally used methods of Zn supply to plants via soil or foliar fertilization. A field experiment with 12-yr-old 'Nagpur' mandarin (Citrus reticulata Blanco) orchard was, therefore, carried out during 2004-07 comparing soil application versus foliar application of Zn, each at three levels viz., 100, 200, and 300 g tree-1 with constant doses of N (600 g tree-1), P (200 g tree-1), K (300 g tree-1), and Fe(60 g tree-1) on Haplustert soil type with reference to response on flowering intensity, fruit set, tree volume, fruit yield, changes in soil fertility/leaf nutrient status, fruit quality, and transformation of native soil Zn fractions. Soil application of Zn at all the three levels, produced significantly higher increase in tree volume over foliar application on equivalent rates viz., T1 (2.53 m3) vs. T4 (2.06 m3) and T2(4.30 m3) vs. T5 (2.23 m3). The yield-determining parameters like flowering and fruit set intensity (no. m-1 shoot length) were, respectively, much higher with soil applied (135.74 and 21.90) than foliar applied Zn (31.20 and 11.6). These observations set the favorable conditions required for yield response, e.g., all the three treatments involving soil application of Zn, T1 (32.1 kg tree-1), T2 (52.6 kg tree-1), and T3 (51.8 kg tree-1) were correspondingly superior over T4 (22.5 kg tree-1), T5 (34.3 kg tree-1), and T6 (42.1 kg tree-1) as foliar application treatments. All the three major fruit quality parameters (juice, acidity, and TSS) were likewise more influenced by soil application than foliar application of Zn. Improvements in soil Zn fractions (mg kg-1) viz., exchangeable Zn (0.25-0.60), complex-Zn (2.71 to 4.86), organically bound Zn (0.86 to 2.0), and Zn-bound to carbonates and acid soluble minerals (2.56-4.96) were observed in response to Zn fertilization with treatments T1-T3. On the other hand, foliar applied Zn treatments (T4-T6) produced no such changes in any of the soil Zn fractions.