Determining of the diagnostic norms for corn on the calcareous soils of Iran

The Diagnosis and Recommendation Integrated System (DRIS) has been successfully applied to many different annual and perennial crops. This system represents an approach to the nutrient contents of crops and is in fact an integrated set of norms. The successful applicability of DRIS to crops as a foliar diagnostic tool has demonstrated a need for the development of DRIS norm for corn in calcareous soils of Iran. Preliminary DRIS norm for corn (Zea mays L.) was developed from more than 50 sets of data on both plant and soil composition of high‐yielding population farms for the years of 1988 and 1989. Soil and leaf samples of com plants were taken at the silking stage. Soil and plant samples were analyzed by conventional methods. Letzch and Sumner's (1983) norms was taken as independent indices for DRIS data. Based on the almost average amount of nutrients in the leaf samples of high‐yielding populations, preliminary DRIS norms have been suggested as follows: N = 2.50; P = 0.25; K = 2.20; Ca = 0.50, and Mg = 0.25 percent, and Fe = 300; Mn = 80; Zn = 20; Cu = 8; and B = 20 ppm. Indices from suggested norms as well as Letzsch and Sumner's norms showed that in spite of similarity among diagnosis and order of nutrient requirement, there was no significant differences between these norms except for nitrogen and zinc. Correlation coefficients between soil and plant analysis data were negligible. Due to the lower amount of organic matter and water shortage, it is difficult to increase the percentage of nitrogen in the leaf samples to above 3.00 percent. With the high P‐ and zero ‐Zn application (higher P/Zn) which is a common practice in calcareous soils, zinc deficiency symptoms will be observed and yield will he decreased accordingly.