Nitrogen, Phosphorus, and Potassium Content of the Corn Leaf and Grain as Related to Nitrogen Fertilization and Yield

On a series of eight nitrogen side-dressing experiments in 1950, a study was conducted to determine the effectiveness of side-dressed nitrogen on corn as shown by yield response and by the chemical composition of the corn leaf and grain. A wide range in response to nitrogen occurred. The application of nitrogen significantly increased the percent of nitrogen in the leaf on all experiments, whereas, the nitrogen content of the grain was significantly increased on only five of the eight experiments. Phosphorus percentage in the leaf was significantly increased due to nitrogen application on certain experiments; and these increases were associated with yield responses which proved to be independent of the nitrogen effect. That a definite relationship between yield and the nitrogen and phosphorus content of the leaf existed in these experiments was shown by determining the regression of yield on the content of these nutrients. Both of the regression coefficients were significant and the multiple correlation coefficient was highly significant. When the nitrogen percentage in the leaf reached the level of approximately 2.8 or above, further increases did not appear to affect corn yields. A very striking linear relationship was found to exist between increases in yield resulting from nitrogen fertilization and associated increases in the nitrogen content of the leaf, the correlation coefficient being 0.96. The results of plant analysis suggest that phosphorus deficiency was a factor limiting yields on four of the experiments. Chemical soil tests for available phosphorus did not distinguish between five of the experiments which, however, appeared to differ in phosphorus status on the basis of phosphorus content of the leaf. In these experiments, leaf analysis provided a clearer indication of the nutrient status of the plants than did grain analysis for all three nutrients.