Diagnosis of leaf nutrient levels for optimum productivity of Citrus reticulata Blanco grown in black clay soils under a sub-humid tropical climate

Abstract

Nagpur mandarin {Citrus reticulata Blanco) orchards under hot sub-humid tropical climate of Central India were surveyed with a view to diagnose the nutrient constraints through leaf and soil analysis, to understand comparative reliability of leaf versus soil analysis and to identify optimum and critical leaf nutrient levels vis-a-vis fruit yield. A total of 178 km2 of Nagpur mandarin growing areas was surveyed covering 112 sites of Central India having black montmorillonitic clay soils. Five to seven months old middle leaves ( 2nd, 3rd or 4th leaf from non-fruiting shoots) were collected at a height of 1.5 to 1.8 m from the ground. The soil samples were collected at a depth of 0-20 cm and at a distance of 110 to 125 cm from the trunk. The collected leaf and soil samples were analyzed for N, P, K, Ca and Mg content. The leaf analysis showed that nitrogen was deficient in 60.1% orchards, phosphorus low to deficient in 37.7% orchards and potassium was in optimum to high range in as many as 77.6% orchards. Despite sufficient K level as per foliar analysis, the response to K fertilization suggested a hidden- hunger for K. The leaf Ca and Mg levels were found to be low to deficient in 99.6% and 64.1% orchards, respectively. But the soils possessed high available Ca + Mg (871.2 mg kg1) and K (188.0 mg kg'1) on an average. Under such conditions, the competition between K and Ca or Mg ions at the soil-root interface restricted the uptake of Ca and Mg ions which resulted in low leaf Ca and Mg levels. The leaf nutrient values were more correlated with fruit yield than soil available nutrients. The degree of relationship was still higher in quadratic than in linear correlation analysis. It is suggested that leaf nutrients levels as of: N 2.34%, P 0.08%, K 1.56%, Ca 1.51% and Mg 0.67% for optimum fruit yield of 636.4 fruits plant'1. The critical leaf nutrient level was observed as : N 2.0%, P 0.06%, K 1.35%, Ca 1.35% and Mg 0.23% for fruit yield of 600.0 plant'1. The above information could be fittingly utilised for nutritional evaluation of Nagpur mandarin orchards.