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Full Text: 1 Introduction Role of micronutrients in balanced plant nutrition is well established. Micronutrients are very important for maintaining soil health and also in increasing productivity of crops (Rattan et al., 2009). Application of Mg + Cu + Zn gave the highest fruit yield of orange but did not affect fruit quality (Ram & Bose, 2000). Sweet orange fruit yield was increased with foliar application of 0.4 kg Zn ha-1 and 0.2 kg Mn ha-1 in the presence of 1.56 kg N ha-1 (Tariq et al., 2007). Foliar spray of CuSO4 (0.4 %) at pea stage and gravel stage increased the fruit retention of Nagpur mandarin was reported by Soni et al. (2017). Flourishes in the growth and yield attributes of Mandarin orange was noticed with foliar spray of micronutrients (Kumar et al., 2017). Foliar application of micronutrients gave the higher Kinnow mandarin fruit yield than the soil treatment under semi-arid zone (Vijaya et al., 2017). However, exploitive nature of modern agriculture involving use of high analysis NPK fertilizers coupled with limited use of organic manure and less recycling of crop residues are important factors contributing towards accelerated exhaustion of micronutrients from the soil (Sharma & Choudhary, 2007). Continuous negligence of micronutrient application and avoidance of organic manures are the major causes of deficiency of these micronutrients (Srivastava et al., 2017). Moreover, citrus is deep rooted plant, micronutrients application at the soil surface may be of a little value. Therefore, a major constraint for productivity and sustainability of the Indian soils were due to the deficiency of micronutrients in the surface soil as well as sub-surface soil. The availability of micronutrients to plants is also influenced by the distribution within the soil profile (Singh & Dhankar, 1989). The knowledge of pedogenic distribution of micronutrients is important as many plant roots penetrate to the sub-surface layers and thus, draw a part of the nutrient requirement from the sub-surface horizon of the soils. The distribution of micronutrient cations of orange orchards of Tamenglong district of Manipur was not yet studied. Therefore, the present work has been undertaken to assess the distribution of micronutrient cations of the orange orchards and to find out the relationship between the soil properties and micronutrients. 2 Materials and Methods The studied area lies between 24045′N to 24059′N latitudes and 93026′ longitudes and located in South-western part of Manipur, India with an elevation of 900-1200 m MSL. Sixteen typical soil profiles from different orchards of Tamenglong District, Manipur were exposed and soil samples were collected depth-wise i.e. 0-20, 20-40, 40-60 and 60-80 cm. in the clean polythene bags. All the composite soil samples were air-dried in the shade, ground and passed through 2 mm sieve for chemical analysis. Typical soil profiles were exposed by collecting depth wise i.e. 0-20, 20-40, 40-60 and 60-80 cm soil samples. These were processed and analyzed for various physicochemical properties like sand, silt, clay content, pH, EC (1:2.5 soil: water), organic carbon, CEC, available N, P and K, Al2O3 and Fe2O3 using standard laboratory procedures outline by Jackson (1973), Borah et al. (1987) and Chopra & Kanwar (1976). The DTPA-extractable Zn, Cu, Fe and Mn in the soil samples were extracted with a solution of 0.005M DTPA, 0.01M CaCl2 and 0.1M tri-ethanolamine adjusted to pH 7.3 as outlined by Lindsay & Norvell (1978). This micronutrient cations concentration in the soils was analyzed by using AAS. Multiple regression equations were computed between DTPA-extractable micronutrients and soil properties by adopting statistical procedures (Panse & Sukhatme, 1961). 3 Results and Discussion The relevant soil characteristics of the representative soil profiles are describe in Table 1. No definite pattern was found in the distribution of sand, silt, and clay content in the profile i.e. 11.8 to 45.2, 5.0 to 32.9 and 37.3 to 62.3 per cent, respectively. The EC of the soils varied from 0.011 to 0.256 dSm-1 and soil organic carbon ranged from 4.2 to 18.6 g kg-1. Organic carbon in surface soil layers was more than the sub-surface layers. CEC ranged from 9.6 to 24.0 [cmol(p+)]kg-1 soil. Free oxides of iron and aluminum varied from 0.2 to 0.6 and 5.7 to 13.5 per cent, respectively. The exchangeable Ca and Mg content in the soils were 0.39 to 7.85 and 0.13 to 5.00 [cmol(p+)]kg-1 soil, respectively, both bases decreased with increased in depth in all the soil profiles. The available N, P and K content in the soils were 125.0 to 313.0, 2.2 to 22.4 and 39.2 to 269.0 kg ha-1, respectively. These nutrients content decreased with increased the depth in the profile. 3.1 Zinc (Zn) DTPA-extractable Zn in the studied soil profiles varied from trace to 1.75 mg kg-1 in the orange growing soils of Tamenglong district of Manipur. Sen et al. (1997) reported the available Zn content varies from 0.2 to 1.4 mg kg-1 and decreased down the profile (Khanday et al., 2017). Similar report was also reported by Athokpam et al. (2016) in the citrus orchard of Ukhrul district, Manipur. Considering 0.6 mg kg-1 as the critical limit of available Zn as suggested by Takkar & Mann (1975), 73.4, 25.0 and 1.6 percent of the studied soil samples fell in deficient, marginal and sufficient categories, respectively. DTPA-extractable Zn showed significant regression (Table 3) with EC (0.868*) and Fe (0.024*).   Table 1 Physico-chemical properties of the soil profiles  
Depth (cm) Sand (%) Silt (%) Clay (%) Texture pH EC (dS m -1) OC (gkg-1) CEC [cmol (p+) kg-1] Fe2O3 (%) Al2O3 (%) Ca [cmol(p+) kg-1] Mg [cmol (p+) kg-1] N (kg ha-1) P (kg ha-1) K (kg ha-1) Profile 1(Longmai Noney II) 0 – 20 39.3 22.5 38.2 CL 4.70 0.084 1.41 15.2 0.56 6.7 0.93 2.70 250.88 15.68 95.2 20 – 40 36.8 25.0 38.2 CL 4.80 0.032 0.66 14.0 0.48 6.2 0.73 1.92 313.60 13.44 50.4 40 – 60 36.8 22.5 40.7 C4.9 4.90 0.015 0.51 13.6 0.32 6.0 1.00 1.93 188.16 13.44 39.2 60 – 80 39.3 17.5 43.2 C 5.00  
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