DRIS Approach for Nitrogen, Phosphorus and Potassium Foliar Diagnostic Norms for Lychee (Litchi chinensis)

The Diagnosis and Recommendation Integrated System (DRIS) was applied for developing N, P and K foliar diagnostic norms for Iychee (Litchi chinensis Sonn.). DRIS assessed the nutrient balance in plant tissues and identified not only the most limiting element, but also the order in which the other elements would become limiting. DRIS norms were computed from elemental (NPK) leaf composition and corresponding yields. The population of observation was divided into two sub-population on the basis of yields. Forms of N, P and K expressions, which significantly discriminated between the two sub-population, were used to calculate the diagnostic norms. The degree of nutrient imbalance in the lychee tree was expressed in terms of DRIS index, which measures the extent to which a particular nutrient deviate from the established norm. The results show that DRIS system can be used irrespective of variety, position of leaf sampled and the time of sampling. The advantage of DRIS system in predicting nutrient imbalances even when the nutrient concentrations in the tree is in or above critical or sufficiency level range, is illustrated.