FOLIAR DIAGNOSIS: THE INFLUENCE OF THE SOIL ON THE ACTION OF FERTILIZERS

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Abstract
The foliar diagnoses (Plant Physiology 12: 571-600. 1937) of similarly fertilized duplicate pairs of plots from a long-continued field expt. with potatoes were compared. The differences in the relative yields of couplets as the result of soil variation ranged from 4.7% to 54.8% and reflected differences in the nutrition of couplets with respect to the intensity and also to the quality. These differences in the 4th leaf from the base sampled at 4 dates during the growth cycle are examined with the aid of graphs showing the changes in the intensities and in the N-P2O5-K2O equilibrium from one sampling to another. In 9 out of 13 pairs of treatments higher intensity of nutrition is accompanied by higher yields. In 7 of these 9 cases the higher intensity is the result of an increase in the K2O of the NPK-unit; in the other 2 cases the higher intensity is the result of an increase in the N of the NPK-unit. In 4 cases higher intensity of nutrition is accompanied by lower yields with, in one case, the lower yielding plot having abnormally low P2O5 in the NPK-unit. The foliar diagnosis of 2 of the couplets viz. [N] and [P] are anomalous in that both the intensity of nutrition and the composition of the NPK-unit of the higher yielding duplicate is furthest removed from the optimum intensity of the optimum NPK-unit.