Department of Plant Sciences

Productivity of mango in India is low at 6.5 t/ha. Among field crops Zn deficiency is the most important disorder and in mango also it was widespread. A survey of the mango orchards of India to identify cause for Zn deficiency indicated that widespread visible zinc deficiencies were noticed in all the four agro-climatic zones in the acid, neutral and high pH alfisols of all the states (pH range 4.8 to pH 7.8). But the analysis of soil indicated adequate DTPA extractable Zn level of 0.75 to 2.2 mg/kg. But about 20% of the orchards showed visible symptoms of Zn deficiency and 40% of the orchards showed leaf Zn in the range of 12 – 17 mg/kg, which is classified as deficient. The high soil Zn level was not reflected in the leaf zinc. A study was carried out to investigate the cause for Zn deficiency in a Zn adequate soil. In pots of 25 litre volume 10 banana plants of Cv. Robusta known for fast growth and nutrient uptake and grafts of Mango Cv. Alphonso known for susceptibility to zinc with 0.75 DTPA Zn were grown for 6 months. After 6 months both banana and mango leaves were analyzed. The banana was healthy with a leaf zinc content of 33 mg/kg whereas Mango had a leaf Zn of 18 mg/kg only. The pH of the rhizosphere soil in banana was 6.2 with a DTPA Zn of 1.2 ppm whereas the pH was 7.0 in Mango with a DTPA Zn of 0.76 ppm. The capacity of banana to acidify the soil to extract native Zn whereas mango is unable to use the same mechanism.