DRIS Norms and their Field Validation in Nagpur Mandarin

ABSTRACT

Diagnosis and recommendation integrated system (DRIS) norms were computed from the data on leaf mineral composition, soil available nutrients, and corresponding mean fruit yield of three years (1999–2002), collected from the set of 57 irrigated commercial ‘Nagpur’ mandarin (budded on Citrus jambhiri Lush) orchards, representing 26 locations and 3 basalt derived soil orders (Entisols, Inceptisols, and Vertisols) rich in smectite minerals. The DRIS norms derived primarily from spring-cycle index leaves from non-fruiting terminals sampled during August to October (6–8 months old) suggested optimum leaf macronutrient concentration (%) as: 1.70–2.81 nitrogen (N), 0.09–0.15 phosphorus (P), 1.02–2.59 potassium (K), 1.80–3.28 calcium (Ca), and 0.43–0.92 magnesium (Mg). While, optimum level of micronutrients (ppm) was determined as: 74.9–113.4 iron (Fe), 54.8–84.6 manganese (Mn), 9.8–17.6 copper (Cu), and 13.6–29.6 zinc (Zn) in relation to fruit yield of 47.7–117.2 kg tree^{? 1}. Likewise, DRIS indices for soil fertility developed from dripline soil samples collected at 0–20 cm depth corresponding to similar level of fruit yield, the optimum limit of soil available nutrients (mg kg^{? 1}) was observed as: 94.8–154.8 N, 6.6–15.9 P, 146.6–311.9 K, 401.0–601.6 Ca, 85.2–369.6 Mg, 10.9–25.2 Fe, 7.5–23.2 Mn, 2.5–5.1 Cu, and 0.59–1.26 Zn. Primary DRIS indices developed on the basis of leaf and soil analysis revealed deficiency of N, P, K, Fe, and Zn. The nutrient constraints so diagnosed were further verified through fertilizer response studies carried out on a representative Typic Haplustert soil type facing multiple nutrient deficiencies, and accordingly suggested the revised fertilizer schedule.