Interpretation of Foliar Analyses for Diagnostic Purposes 1

The precision and flexibility of various foliar techniques in making valid diagnoses of mineral imbalances in plants have seldom been critically evaluated. This paper compares the classical critical value approach with the newer Diagnosis and Recommendation Integrated System (DRIS) in evaluating diagnoses from the same sets of data. The critical value and sufficiency range norms for various crops are presented and from these, DRIS indices are calculated for comparative purposes. Although the norms for both approaches depart from essentially similar reference points, the DRIS approach is able to make diagnoses meaningfully over a range of plant ages and can classify the order in which nutrients limit yield. Comparisons of diagnostic precision between the two systems are made using data from various field experiments with corn, ( Zea mays L.), soybeans ( Glycine max L.), sugarcane ( Saccharum officinarum L.), and potatoes ( Solanum tuberosum L.). These comparisons are achieved by comparing yields on treatments with and without a particular nutrient which has been diagnosed as being limiting. A yield increase when the particular nutrient is applied indicates that the diagnosis was correct and vice versa, Overall, DRIS is superior to the critical value approach in that it is able to make valid diagnoses more frequently because variations due to tissue age are taken into account.