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.
