Kinnow mandarin is predominately grown in the north-western region of India, such as Punjab, Haryana, Himachal Pradesh, western Rajasthan and Uttar Pradesh. It was introduced in 1956 in Punjab which helped in replacing the traditional citrus fruits viz., sweet orange and local mandarin to some extent and strengthening the status of citrus industry in India and thereby making India as the sixth largest producer (3.79 million tonnes/annum) in the world with a shareof 4.8 percent (Ghosh, 10).

The greatest single factor holding chief responsibility for citrus decline being witnessed by the north-eastern states of India at an alarming rate is the poor nutrient status of the soil (Randhawa, 17). Deficiency of any element considered essential among the sixteen leads to altered metabolism and subsequently resulting in physiological changes and poor productivity (Balakrishnan et al., 1). Chapman (4) reported substantial removal of macro as well as micronutrients by citrus fruits. Widespread micronutrient deficiency occurs in different states and majority of the orchardists do not follow micronutrient application and their orchards show the hunger signs (Bojappa and Bhargava, 2). Among the micronutrients, zinc deficiency is the most widespread which alone occupies eleven percent of the cultivated area in India (Ganeshmoorthy et al., 9). There is a specific need of zinc spray to mandarin orchards in acid alfisol of Meghalaya as the soil is deficient in zinc due to the acidic soil reaction and leaching caused by excessive rainfall (Patiram, 15). Foliar spray of zinc sulphate (0.5%) improved the general condition of the Kinnow plants (Mukherjee, 13) and decreased the die-back of twigs and leaf chlorosis (Chaudhari, 5). Kinnow mandarin orchards sprayed with zinc resulted in the production of better sized fruits (Dikshit et al., 6). Therefore, realizing the importance of essential elements in plant nutrition, the present study was taken up to establish the effect of magnesium, zinc and manganese on enhancing productivity and quality of Kinnow mandarin.

The experiment was conducted at the experimental farm of the Division of Horticulture, ICAR Research Complex for NEH Region, Umiam, Meghalaya during 2000 to 2002. The soil type of the orchard is alfisol with an acidic pH of 4.5. The experiment was laid out in randomized block design with four replications on ten-year old Kinnow mandarin trees of uniform size and vigour. The treatments comprised one level each of magnesium sulphate (0.5%), zinc sulphate (0.5%) and manganese sulphate (0.5%) and the nutrients were applied through foliar spray singly and in various double and triple combination(s). The required amount of nutrients was dissolved separately in water and the pH of the solution was adjusted to neutral by adding lime and sprayed twice during May and September. Observations on productivity parameters (fruit weight, fruit volume, fruit length, fruit diameter and yield/tree) and quality parameters total soluble solids (TSS), titrable acidity, ascorbic acid and juice content were recorded from the freshly harvested fruits during December. The TSS (%) of the fruit juice was recorded using hand refractometer and by applying the correction factor for 20°C. The titrable acidity was estimated and expressed as percent citric acid (Ranganna, 18). The ascorbic acid content (mg/100 g) was estimated as per the method described by Sadasivam and Manickam (19). The experiment was carried out under clean culture conditions.

Outcome from productivity parameters (Table 1) revealed that the number of fruits/tree varied significantly and it ranged from 126.25 to 246.00. The maximum number of fruit (246.00) was recorded by the trees sprayed with zinc and manganese whereas it was the minimum (126.25) from control. Saraswathi et al. (20) also observed that the supplementation of essential elements has brought out a significant increase in the number of fruits/tree in mandarin orange. Zinc is involved in protein synthesis and has direct influence on the level of auxin (indole-3-acetic acid) in plants (Keilina and Mann, 12; Skoog, 22) that is responsible for increased fruit retention by the tree. The treatment with essential elements was also found to be beneficial in improving fruit weight, fruit volume, fruit length and fruit diameter. Maximum fruit weight, fruit volume and fruit length were recorded by the trees sprayed with magnesium, zinc and manganese whereas the untreated control (water spray) registered the minimum values for these characters. The beneficial effect of micronutrients in increasing the fruit volume through their direct involvement was well recognised by Singh et al. (21). Magnesium, being the metallic constituent of chlorophyll, is directly involved in the process of photosynthesis besides regulating the uptake of other nutrients (Willstates, 25). The beneficial effect of manganese on growth and nutrition of mandarin orange was well-observed by earlier workers Ghosh et al. (11) and Calvert (3).

Spray of essential elements either singly or in combination proved to be very effective in obtaining a higher productivity. The yield/tree varied considerably and increased significantly with supplementation of essential elements. The highest productivity (34.07 kg/tree) was recorded with zinc and manganese spray. The yield enhancement might be due to the large plant spread obtained by the supply of essential elements in ample amount which resulted in improved growth, better flowering and higher fruitset over the control. Smith (23) was also of the opinion that an increase in tree volume increases the fruit bearing area. This is in line with the earlier findings in Kinnow mandarin (Nijjar and Brar, 14), California lemon (Embelton et al., 8) and acid lime (Edward Raja and Anjaneyalu, 7).

Foliar application of essential nutrients on quality attributes of Kinnow mandarin (Table 2) revealed that the total soluble solids varied considerably from 9.90 to 10.85 percent and the treatments did not differ significantly with respect to their ability to improve total soluble solids. The maximum TSS was recorded by the fruits obtained from the trees sprayed with magnesium, zinc and manganese whereas the control registered the minimum TSS. In contrary to TSS, the acidity was maximum in control and less in treated trees with the minimum in trees sprayed with magnesium, zinc and manganese. Though the foliar spray of secondary and trace elements has increased the TSS and reduced the titrable acidity of the fruit juice, the variations were statistically non-significant. This agrees with the reports of Ram and Bose (16) in mandarin orange. The ascorbic acid (vitamin C) content of the fruit juice increased considerably with nutrient fortification and it ranged from 22.50 to 37.50 mg/100g. The control registered the minimum value whereas the treated trees were high in ascorbic acid with the maximum from the trees sprayed with magnesium, zinc and manganese. This closely follows the findings of Tayde and Ingle (24) who studied the effect of micronutrients on the quality of Nagpur mandarin.

An increase in juice content of the fruits was brought out by foliar spray of essential (trace and secondary) elements. The maximum juice content (44.0%) was obtained with magnesium, zinc and manganese whereas the control registered the minimum juice content. The TSS/acid ratio was found to be in the range of 9.9 and 13.0 in the fruit juice. The control registered the lowest value for TSS/acid ratio whereas the highest by the fruits of the trees sprayed with magnesium, zinc and manganese. In general, the quality attributes of Kinnow mandarin were not significantly influenced by the foliar fertilization of essential secondary and trace elements.

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