India produces in considerable quantity a variety of citrus fruits like grape fruit, lemons, limes, sweet oranges, mandarins and kinnow. Citrus fruits are cultivated in India in an area of 1055 thousand ha. and produces 12.75 million tones. Response of micronutrients particularly, Zn, has been noted for increasing the quality and yield of citrus fruits, besides shelf life of. An appraisal on Zn nutrient deficiencies and superimposing citrus crop for district-wise crop based Zn nutrient delineation maps is essential for preparing strategic guide in realizing potential yields of different citrus crops in different regions of the country.
Crop Boundary:
Eleven states covering 131districts were identified as prime citrus growing states of India. Boundary map of citrus was prepared using district maps of respective leading producing states (Figure 1). Although, 131 districts are producing citrus, the species of citrus vary from one region to another. For example Vidarba region of Central India (Maharashtra and Madhya Pradesh) grow mostly Nagpur mandarins and acid limes, while Punjab grows Kinnow. Similarly Coorg and Neelgiris grow Coorg mandarins, while northeastern states grow Khasi mandarins. Andhra Pradesh, Telanganaand Karnataka produce most of the sathgudi sweet oranges and limes. Irrespective of these differences in crops species the citrus map is prepared as one unit combining all these cultivated species.
Figure 1.Major citrus growing areas in India:
Deficiency symptoms:
Zinc deficiency has traditionally been the most widespread deficiency in citrus.
Development of visual symptoms of Zinc deficiency follows the following progression:
Zn-deficiency: Typical symptoms include reduction in size of leaves, typical interveinal chlorosis, trenching and rossetting of leaves, profuse water suckers and ultimate decline of twigs.
Seven distinctive stages in zinc deficiency in citrus may be seen in most citrus species. A stage wise description of the deficiency is presented below(Plate 3A to 3I): In stage I (Plate A)young growth is first affected, Which is characterized by cholotic and necrotic leaves, later turning into smalling, multiple sprouting, trenching and rosetting appearance. As deficiency advance to stage II(Plate B, C), relatives amount of green and yellow tissue vary from a condition of mild Zn deficiency in which there are only small yellow splotches between the larger lateral veins to a condition characterized by green basal portion of the mid rib and remainder of the leaf as yellow to white. In stage III(Plate D and E), whitish chlorotic streaks between veins in older leaves and whitening of upper leaves are characterized by green bands along the mid-rib and main vein on a background of light yellow to almost white. As it advances to stage IV (Plate F)in very acute stages, the leaves are pointed abnormally narrow with the tendency to stand upright, and extremely reduced in size. In stage V(Plate G), as the deficiency progresses, the leaves are affected over the entire periphery of the tree, and the twigs become very thin and die back rapidly. Then in stage VI(Plate H), Profuse development of water sprouts takes place on the main branches, trunk and with leaves free from deficiency symptoms. Ultimately in stage VII(Plate I), the trees display a dense growth at the centre with dying appearance over its periphery
Zinc fertility status of citrus growing regions of India:The citrus zinc map(Figure 2) prepared using the soil DTPA zinc status of Indian soils shows that out of 131 citrus districts, 44 districts are reported to be low in available zinc and 63 districts were reported to be well supplied with soil zinc. For 18% of the citrus growing districts (24 districts) no information is available on soil zinc status. Keeping this in mind and the pattern of fertilizer use in citrus and the crop ability to absorb nutrients it is advisable to go for foliar application of zinc rather than soil application as a precaution to avoid unnecessary accumulation in the soils leading to nutrient imbalances.
Figure 2. Zinc fertility status of citrus growing regions of India
Management of Zinc in Citrus crops:
Zinc deficiency in citrus, can be ameliorated by foliar application of zinc sulphate. Spray the plants with 0.25-0.5% zinc sulphate solution (250-500g zinc sulphate per 100 liters of water depending upon severity of deficiency) during April-May on new flushes. However, in some places where new flush emerges late, the spray should be done in June and if further delayed flush appears then zinc sulphate should be sprayed during August-September. Apart from this in citrus, zinc deficiency becomes acute immediately after first fruit set on plants; therefore one maintenance spray of 0.3% zinc sulphate solution may be given in pre-monsoon from the third year of planting.
Like other micronutrients, foliar spray is more useful over soil fertilization. Foliar spray of ZnSO4 at the rate of 0.30-0.50% (‘Kinnow’ mandarin), 0.5% (‘Nagpur’ mandarin and ‘Sathgudi’ sweet orange), 0.30-0.60% (‘Kagzi; lime), 0.15% (‘Jaffa’ sweet orange),1.0% (‘Coorg’ mandarin) and 0.40% Zn-EDTA (‘Pant’ lemon) has observed very effective in combating Zn-deficiency. On the other hand, soil application of ZnSO4 at the rate of 50-100 g tree-1year-1(‘Sathgudi’ sweet orange), 300 g tree-1year-1 (‘Nagpur’ mandarin), 250-1000 g tree-1year-1 (‘Kinnow’ mandarin), 500 g tree-1year-1(‘Blood’ red sweet orange), 294-810 g tree-1year-1 (‘Pant’ lemon) and 10-15 g Zn-EDTA (‘Jaffa’ sweet orange) have proved very effective with regard to recovery of treated plants from Zn-deficiency. However annual application should be avoided to prevent accumulation in soil. Hence soil testing at regular interval is recommended before deciding on soil Zn application to citrus crop.
Image Credits : medium.com/@quickgardenn/citrus-fruits-af98dcb08937
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