Corn leaf samples were taken at different positions of the stalk in order to find out the best correlation between N content in the leaf and grain yield. The experiment was carried out on a Ortho-Red-Yellow soil at Mococa Experimental Station. The experiment was a randomized block design with five replications. The treatments consisted of application as side dressing of 0, 30 and 60 kg N/ha as ammonium sulphate. At planting time the quantity of fertilizer applied was 300 kg/ha of the formula 4-14-8. At flowering, leaf +4, ear leaf and the leaf below and opposite to the first corn ear were sampled. The leaves from the three sampling methods and the grain yield at harvesting time were analysed for total N, P, K, Ca, Mg and S. The application of S fertilizer showed pronounced effect on the content of N in the leaves +4. There were no significant differences among correlation coefficients obtained between N content of the different leaves and grain yield. Further, the N fertilizer had a positive effect on the P Ca and S content of the leaves +4, on the P and S content of ear leaves and on the K content of the leaves below and opposite to the first corn ear. Nitrogen application did not have a pronounced effect on the content of nutrientes in the grain yield. The leaf +4 showed the least coefficient of variation for nitrogen nutrition diagnosis.