In the light of global occurrence of multi-nutrient deficiency – induced production constraint of citrus orchards, a variety of nutrient diagnostic techniques are under recurrent use, test, and scrutiny. Of different test methods, leaf analysis has shown better commercial application with regard to identifying nutrient constraints addressing to field conditions. However, of late, the precision of diagnosis is further influenced by the type of interpretation tools used. In this background information, large scale survey of Nagpur mandarin orchards in central India representing sub-humid tropical climate were surveyed. Five-to-seven month old index leaves from non-fruiting terminals were subject to analysis of nutrient composition and establishing optimum values through statistical models like Multivariate Quadratic Regression (MQR) - Diagnosis and Recommendation Integrated System (DRIS) verified through site specific progressive nutrient response experiment. DRIS analysis suggested the optimum leaf nutrient concentration as: 1.70-2.81% N, 0.09-0.15% P, 1.02-2.59 K%, 1.80-3.28 Ca%, 0.43-0.92 Mg%, 74.9-113.4 ppm Fe, 54.8-84.6 ppm Mn, 9.8-17.6 ppm Cu, and 13.6-29.6 ppm Zn in relation to fruit yield of 48-117 kg/tree. These values when determined through MQR were by contrast different as: 2.2-2.4 N%, 0.07-0.10 %P, 1.2-1.6% K, 1.3-1.5%Ca, 0.48-0.67% Mg, 110-132 ppm Fe, 49-43 ppm Mn, 8-14 ppm Cu, and 18-30 ppm Zn in relation to yield of 40-54 kg/tree. The deficiency of NPKFeZn only was established using primary DRIS indices and MQR, respectively. Fertilizer response studies carried out on a representative Typic Haplustert soil type facing multiple nutrient deficiencies showed the significant response of Nagpur mandarin to treatments involving NPKFeZn as diagnosed through DRIS instead of MQR. Both the micronutrients Zn and Fe registered a negative DRIS index as –18 and –20 with N1P2K2Zn0Fe1 and N1P1K1Zn1Fe0, respectively, which significantly improved with treatments supplying both the nutrients. Increasing the nutrient doses reduced the sum of DRIS indices irrespective of sign from 164 (N0P1K1Zn1Fe1) to as low as 38 (N2P3K1Zn1Fe1) registering the highest fruit yield (58.8 kg/tree). These responses are suggestive of variation in diagnostic precision as per the interpretation tools.