Abstract
The Diagnostic Recommendation and Integrated System (DRIS) and a critical concentration approach were used to identify mineral nutrient deficiencies in papaya (Papaya carica L., cv. Solo) trees grown with defined nutrient solutions in sand culture in the glasshouse and under commercial field conditions. DRIS indices for sand-cultured trees that manifested no mineral nutrient deficiency symptoms, i.e. the 'complete' treatment, were all positive, indicating that indeed no nutrients were limiting plant growth and development. The most deficient elements in petioles of recently-matured leaves from field-grown trees with visually-discernible deficiencies, according to DRIS, were P, Fe and Zn. The concentration of P was below the critical level in all trees that manifested any visual symptoms of nutritional imbalance. This was confirmed by the negative DRIS indices for these trees. The DRIS indices for Fe and Zn were also negative, indicating that concentrations of these micronutrients may not have been sufficient. However, the actual tissue concentrations of Fe and Zn were well within, or even above, the range of adequacy. Toxicity could thus be a contributing factor in symptoms expression, particularly for Zn. Magnesium concentrations increased in unhealthy trees compared with the healthy ones but the DRIS indices failed to identify this as a contributory factor. DRIS, when used in conjunction with a critical concentration approach to interpreting tissue analysis data, appears to be a useful technique for identifying nutrient deficiencies in papaya.
