We investigated the presence of correlations between changes in parameters of delayed fluorescence of leaf chlorophyll (DFCh) and content in the leaves of protein nitrogen, phosphorus, potassium, and soluble sugars during the period from the start of the fruit formation phase to harvesting of the yield in tomato plants grown at different doses of nitrogen fertilizer. The value of parameters of leaf DFCh can be an indicator of changes in the physiological state of the plant. Amplitude of leaf DFCh is mainly determined by protein content in the leaves, whereas its half-life characterizes changes in the degree of coupling between light and dark reactions of photosynthesis in the plants. It is hypothesized that increase of the yield under the influence of nitrogen fertilizer is mainly dictated by increase in vegetative mass of the plants and for all practical purposes is not determined by maximum fluorescence intensity or protein content in the leaves.
