The physiological assessment of the nutrient status of plants. IV. The effect of the interaction between nutrient elements of leaf area responses

Abstract

Experiments were carried out with subterranean clover in water cultures to study the effect of interactions between phosphorus, sulphur, and nitrogen. These elements were varied in pairs, and leaf area responses measured after transfer to complete solutions and to solutions without one of the two previously varied elements. Leaf area responses after transfer of plants deficient in phosphorus as well as in sulphur revealed both deficiencies when they had been of approximately equal intensity. When elements were deficient to differing degrees, leaf area responses depended on the relative intensities of the deficiencies. With deficiencies of sufficiently differing intensities, leaf area response patterns after transfer showed a deficiency of only one element because its supply had been low enough to mask the effect of the other deficiency. Transfer of plants deficient in only one element confirmed that there is no simple relation between the nitrogen status of the plant and the induced leaf area responses. The results also confirmed the feasibility of at least a qualitative assessment of the phosphorus or the sulphur status of plants.