Extensive surveys were carried out covering as many as 40 orchards of Khasi mandarin in Thangal village of the sub-division Nungba under Tamenglong district in the year 2010-2011. Nutrient constraints in the form of N, P, Ca, Mg, Cu, and Zn were identified using these diagnostics which must find a due place in a fertilizer program of mandarin orchards of the region to obtain sustainable optimum fruit yield. The values of available nutrients viz., N, P, and K across 40 orchards varied from 92.2 to 348.2 mg/kg, 5.0 to 9.4 mg/kg, 110.0 to 440.1 mg/kg, respectively, with corresponding coefficient of variation (%) of 11.8, 9.2, and 16.4 respectively. Soil micronutrients showed a large variation of 11.2- 48.1 mg/kg Fe (CV 16.2%), 11.4-44.0 mg/kg Mn (CV 11.2%), 0.80-2.5 mg/kg Cu (CV 6.9%) and 0.50-2.8 mg/kg Zn (CV 7.4%). Leaf nutrient concentration like soil fertility showed a wide variation from 1.62-2.62 % N, 0.04-0.12% P, 0.72-1.89% K, 0.90-2.24% Ca and 0.28-0.61% Mg. Similarly, the micronutrients, namely Fe, Mn, Cu, and Zn expressed in ppm, varied from 118.4-282.3, 32.3-92.4, 1.0-3.8 and 14.6-28.4. It was observed that maximum nutrients are removed (in mg/tree) in the proportion of 171.90 N, 17.19 P, 34.38 K, 68.76 Ca, 17.19 Mg, 0.34 Zn and 0.20 Cu in relation to an average mean fruit yield of 34.38 (kg/tree) by Khasi mandarin i.e. orchard no. 1. Minimum nutrients are removed (in mg/tree) in the proportion of : 113.75 N, 11.37 P, 22.75 K, 45.50 Ca, 11.37 Mg, 0.22 Zn and 0.13 Cu in relation to an average mean fruit yield of 22.75 (kg/tree) by Khasi mandarin i.e. orchard no. 9. These observations give an insight about the order in which, different nutrients are preferred by specific citrus cultivar, and the ratio in which different nutrients are removed. Such nutrient removal patterns are to be meted out in order to maintain the sustained supply of the nutrients through soil.
