The Influence of Foliar Applications of Urea on the Nodulation Pattern of Certain Leguminous Species

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Abstract
In greenhouse experiments with seven species of legumes, the spraying of urea on to the leaves was shown to affect nodulation adversely, without impairing the growth of the plants. In Phaseolus vulgaris, Vicia sativa, and Pisum sativum three-times-weekly sprays of 1 per cent. aqueous urea either prevented or markedly reduced nodule development during the 8-week experimental period. In Medicago sativa and Trifolium pratense the urea treatment resulted in a delay in nodulation so that numbers of nodules at the first sampling (4 weeks) were reduced, while numbers at later samplings were higher since nodulation had been delayed until the root system was larger and provided a greater number of potential nodule sites. In Trifolium hybridum and T. repens the urea-treated plants showed reduced nodulation throughout the 6-week experimental period. In these experiments the advance effects on nodulation cannot be due to high concentration of combined nitrogen in the rooting medium, but it is suggested they derive from a high level of nitrogen within the plant.

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