DRIS norms for identifying yield limiting micronutrients in cocoa under coconut intercropping systems

Abstract

Cocoa production in the state of Tamil Nadu is severely constrained by the deficiencies of micronutrients viz., iron (Fe), manganese (Mn), zinc (Zn), copper (Cu) and boron (B) resulting in yield loss to the tune of 40 − 50%. A preliminary survey was conducted in forty cocoa growing locations across seven districts of the state to develop diagnostic norms and indices for the yield limiting micronutrients in cocoa population aging more than five years. The whole population was divided into high and low yielding sub populations based on the yield (20 kg pods per plant per year as the critical yield). Index leaf samples and soil samples each numbering 160 were collected and the micronutrients were determined. Nutrient indices were worked out for both the populations adopting Diagnosis and Recommendation Integrated System (DRIS) of Beaufils. The order of limitation of nutrients for higher yield in the plant system was Mn > Cu > Zn > Fe > B. The extent of micronutrient deficiency in the soil system was Zn > Fe > Cu > B > Mn. Micronutrient requirement for cocoa plants is in the order Fe > Mn > B >Zn > Cu. The optimal foliar concentrations of the micronutrients in cocoa under coconut intercropping systems is Fe − 531 mg kg−1, Mn − 90 mg kg−1, Zn − 31 mg kg−1, Cu − 11 mg kg−1 and B − 80 mg kg−1. In low yielding cocoa sub population, DRIS index was positive only for B.