Nitrogen and phosphorus concentrations of white clover genotypes differing in response to added phosphorus

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Abstract
The phosphorus (P) response of 110 white clover (Trifolium repens L.) genotypes was determined in a glasshouse pot experiment. The nitrogen (N) and P contents of leaf, stolon, and flower components were determined for the seven most responsive and seven least responsive genotypes. The most P-responsive genotypes had lower % N and % P levels, lower N/P ratios, but higher total N and P contents compared with the least P-responsive genotypes. While the present study showed that selection for variation in P response may result in associated differences in % P content, the converse was not true. Leaf %N and N/P ratio, which provide an indication of the plant's ability to utilise P for N fixation and N assimilation into dry matter, provided a better explanation of differences in P response than leaf %P alone. Broad-sense heri-tabilities for %P, %N, and N/P ratio in leaf tissue were 0.52, 0.65, and 0.66, respectively, determined over all 110 genotypes at a P level giving 80–90% maximum yield.