The litchi (Litchi chinensis Sonn) an important sub-tropical evergreen fruit crop believed to have originated in China was introduced to India, in the 18th century through Myanmar. Today India produces 583000 metric tonnes of litchi annually from 92,000 hectares.
Litchi plant requires nutrients for satisfactory growth and fruiting. Yield and fruit quality in litchi are only adequate with optimum range of leaf and soil nutrient concentrations. New growth is more dependent on reserves in the tree than on fertilizer applied just recently to the soil. Among micronutrients deficiency of zinc is wide spread and affects crop yield and quality. In the absence of complete information we have attempted to prepare an update on the zinc deficient area, deficiency symptoms and its management in litchi. This appraisal on soil zinc deficiencies and superimposing litchi area for district-wise crop based zinc delineation maps is essential for preparing strategic guide in realizing potential yields of litchi in different regions of the country for efficient management of Zn deficiencies to enhance the yield and quality of litchi.
Litchi crop boundary:
Litchi is grown in few states of the country owing to its preference for specific climatic requirement. It can however, be grown on a variety of soils. Based on area and production, 56 districts spread in ten states were identified as prime litchi producing states of India (Figure 1). The boundary map of litchi was prepared using district maps of respective leading litchi producing states.
Figure 1.Major Litchi growing areas in India:
Deficiency symptoms:
In Litchi, zinc is most important at different stages of plant growth and development, for photosynthesis, root and shoot growth, flowering and fruit set. Zinc availability to Litchi is greatly influenced by soil conditions. Its deficiency is most likely to occur in Litchi grown on alkaline soils where zinc is not readily available to plants. Zinc deficiency occurs on acid leached soils where native zinc is low. However, deficiencies on heavily leached acid soils like in the new areas of Coorg and Neelgiri hills, Dehradun and other hilly areas of Uttarakhand and Himachal Pradesh may also be induced by lime application. These problems are often exacerbated after heavy nitrogen applications. Deficiency symptoms(Plate A,B,C,D) are normally associated with interveinal chlorosis of young leaves, ‘little leaf disease’, poor fruit set and yields. Leaves become small and narrow with leaf margins bent upward or downward. Internodal length is reduced drastically and the twig with crowded leaves gives rosette appearance and interveinal areas turn pale. Trees do not grow well and the yield, size and quality of the fruit are reduced. Zinc deficiency can also causes general bronzing or mottling of the leaves, smaller shoots and smaller fruit, small and short leaves with normal colour and occasional curving. The branches may die when leaf concentrations fall below 10 ppm.
Plate (A,B,C,D). Showing zinc deficiency in Litchi. Symptoms first appear on young leaves (A) with first appearance of interveinal chlorosis. Growth is stunted and as the deficiency advances the interveinal chlorosis becomes severe(B). An young Litchi tree showing severe interveinal chlorosis and little leaf symptoms with crowded leaves giving rosette appearance and a mature Litchi trees(C, D) showing very poor fruit set due to zinc deficiency.
Out of 56 Litchi districts, soils in 71% of area (40 districts) are well supplied with zinc(Figure 2). Only 10.7% area(6 districts) shows deficient levels of soil zinc. Zinc deficiency occurs during peak growth period or fruit development stage when the demand for zinc exceeds supply rate from the soil. Being immobile retranslocation from older leaves or woody part is slow. As a result the deficiency is exhibited both as hidden hunger and as expressed leaf symptoms. Foliar application of zinc corrects such deficiencies.
Figure 2.Zinc fertility status of Litchi growing regions of India
Management of Zinc in Litchi:
Continuous soil application of zinc leads to its accumulation in the soil leading to nutrient imbalance in the soil. Further the uptake of foliar‐applied zinc in Litchi is more rapid than that of soil applied zinc. Hence for correction of zinc deficiency, foliar application is preferred over soil application. 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) soon after cessation of monsoon and before new flush and repeat the spray before panicle emergence. 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 litchi, 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. Micronutrient specials developed by IIHR may be used at 5g per liter to correct zinc deficiency in addition to other micronutrient deficiencies. Those growers who wish to apply Zn to soil may apply one kg zinc sulphate per tree only once in two to three years.
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