Selection of index leaf for foliar diagnosis of critical nutrient levels in physic nut (Jatropha curcas)

Basic information about mineral nutrition of physic nut is scarce.Especially, determination of index leaf to evaluate nutritional status is very rare.Therefore, objective of this study is to find the index leaf, the type and leaf position in the floral branch and propose critical levels of nutrients for nutritional diagnosis of physic nut.The nutrient concentrations in leaf limb, petiole and complete leaf and shoot dry weight of plant were recorded from the experiment under nutrient omissions in greenhouse.The complete leaf samples were also collected from two types of branches (main and lateral) and in three positions (apical, medial and basal of the branch), corresponding to the branches between the first and fourth, between the fifth and eighth and between the ninth and twelfth leaves, respectively, at flowering and seed productivity stages.These data were obtained from an experimental plot of NPK fertilization to define the position of the complete leaf to be sampled and to propose values of critical nutrient levels for physic nut.Critical levels of nutrients were proposed by means of reduced normal distribution criterion with field experiment data.The complete leaf (petiole and leaf limb) in the median position between the fifth and eighth leaves in the main and lateral branches in the full flowering of crop was indicated as sampling standard for the diagnosis of nutritional state of physic nut.In the present work, the critical levels of and macronutrients in leaf sampling were proposed as following (g kg -1 ): 27.8 for N, 1.4 for P, 11.8 for K, 12.8 for Ca, 6.7 for Mg and 1.3 for S and, micronutrients (mg kg -1 ): 78.8 for B, 14.2 for Cu, 139.7 for Fe, 129.3 for Mn and 20.4 for Zn.