The Effect of Nitrogenous Fertilizer on the Photosynthesis and Growth of White Clover/Perennial Ryegrass Swards

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Abstract
The application of nitrogenous fertilizer in March to a white clover (cv. Blanca) and perennial ryegrass (cv. S23) sward resulted in a rapid suppression of the clover, relative to clover in a treatment given no added nitrogen. Thereafter, the clover in both treatments grew more rapidly than the grass and its proportion of the total leaf area in the mixture increased, as the leaf area index rose to 8. After a second application of N in early July, clover was not suppressed to the same extent as in the first growth period. Overall, the photosynthetic capacities of newly expanded clover laminae were similar in the two treatments. Clover laminae had higher photosynthetic capacities than grass, even in the grass-dominant + N treatment. Lamina area, petiole length, and the number of live leaves per stolon were similar in the two treatments, indicating that the differences in total leaf area were due to the presence of fewer stolon growing points in the + N treatment.