Published online by Cambridge University Press: 27 March 2009
All combinations of four levels of potassium and two of nitrogen were applied in each of 2 years to a hill sward on a brown podzolic soil with an 8 cm peaty surface horizon anda very low level of extractable K. The sward had been surface-sown 11 years before with white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.). During the course of the experiment, harvesting was by cutting, with an average interval between cuts of 5 weeks. The previous management had been sheep grazing.
The proportion of clover in harvested herbage was increased by applied K and reduced by applied N. The clover grew strongly in the 1st year of cutting management where K, but no N, was applied, but there was much less clover in the 2nd year on all plots. The concentration of K in both clover and grass was greatly increased by applied K, but only the clover responded strongly in terms of extra herbage produced. This suggests that grass growth was N-limited, whereas the clover had sufficient N from symbiotic fixation.
Applied K increased the size and weight of clover leaves, the rate of extension of the stolon main axis, and the number and length of stolon branches, but did not affect the rate of emergence of leaves on the stolon main axis. Applied N had a generally negative effect on the aspects of clover growth and morphology which were measured. The length and weight per ryegrass leaf blade were generally slightly increased by both applied K and applied N.