Grapes occupies fifth position amongst fruit crops in India with a production of 2.68 million tones from an area of 1.36 million ha(MAFW, 2017). About 80 per cent of the production comes from Maharashtra followed by Karnataka and Tamil Nadu. Grapes is a heavy feeder of nutrients and high yields can only be sustained through the application of optimal doses of fertilizers in balanced proportion. But quality and yields are compromised because of imbalanced use of fertilizers, particularly zinc and other micronutrients. Hence an appraisal on Zn nutrient deficiencies and superimposing grapes crop for district-wise crop based Zn nutrient delineation maps is essential for preparing strategic guide in realizing potential yields and good quality grapes in different regions of the country.
Crop boundary:
Ten states covering 43 districts were identified as prime grapes producing states of India. Using district maps of respective leading producing states, the boundary map of grapes was prepared and is presented in Figure 1 below: Major grapes growing areas in India
Deficiency symptoms:
Zinc deficiency is mostly observed in Nasik and Ahmednagar districts in Maharashtra, Bijapur, Bengaluru, Kolar and Koppal districts of Karnataka and Coimbatore, Dindigul districts of Tamil Nadu. Symptoms appear as interveinal chlorosis of the entire leaf lamina with clear green colour of the veins(Plate A,B,C), stunted lateral shoots with small leaves (little leaf). The small veins remain green with interveinal tissues remaining green-pale yellow. Clusters show poor set and short berries with smallest one remaining green.
Plate. Zinc deficiency in grapes (A) showing interveinal chlorosis of the entire leaf lamina with clear green colour of the veins, (B) mosaic pattern of leaves spreading from young leaf towards middle age leaf (C) shortened internodes leading to bushy appearance of the terminal portion of vines.
Using the zinc fertility status map of India developed by AICRP(MSNPE) and adding additional information available in published papers the grapes growing soils area was delineated for zinc deficiency on the basis of the percentage of samples found deficient in each district and is shown in Figure 2. It is found that of the 43 grapes growing districts soils in 29 districts (67.4%) were well supplied with available zinc and 14 districts (32.6%) soils showed zinc deficiency. The data on the extent of zinc deficiency in grapes growing soils is very high, but one must exercise caution in using this information as most grapes growers are enlightened farmers and regularly use zinc as both soil application and foliar sprays. As a result the soil status of individual vineyards may be high.
Figure 2. Zinc fertility status of grapes growing regions of India
Management of Zinc in Grapes:
Response to applied zinc in grapes is impressive compared to other fruit crops, if the soil status is low. Hence, zinc application should be made to grapes on the basis of soil test. A blanket application of zinc to soils may be avoided as build up would cause more damage than doing good. Zinc concentrations in petioles of seedless grapes range from 25-94 ppm and in seeded grapes from 30-88. If the concentration of zinc in the petioles fall below these levels then corrective measures are required.
Foliar spray of zinc is most common because it is the most widely deficient micronutrient. Treatment can also be quite effective if the correct material and methods of application are used. Neutral solution of zinc sulphate heptahydrate and zinc oxide are the most economical and effective on a recommended label basis. There is no advantage in using chelated zinc products in sprays. They were originally intended for soil application, are more expensive, and less effective than zinc sulphate and zinc oxide. The deficiency of zinc is readily corrected with zinc sulphate heptahydrate and zinc oxide spray at 0.25 to 0.3 per cent depending upon the severity of the deficiency. The optimum timing to influence fruit set is three weeks before bloom up to bloom. Spray of lower concentrations is better than higher concentrations because the uptake is greatest with dilute application.
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