The response of Whitegrass [Cortaderia pilosa (D'Urv.) Hack.] to nitrogen nutrition

To investigate the potential for increasing Falkland Island Whitegrass [Cor taderia pilosa (D'Urv.) Hack.] pasture production through application of ni trogen (N) fertilizer, two hydroponic experiments were conducted. First, 5 mg l(-1) N was supplied to plants as nitrate (NO3-), urea [CO(NH2)(2)], amm onium (NH4+), or a nine parts NH4+ one part NO3- mixture. At harvest, plant s grown in a NO3- medium had about half the biomass of plants grown in a NH 4+ medium. In the second experiment plants were supplied with 1, 3, 10, 30 or 100 mg l(-1) NH4+-N Plants at 1 and 3 mg l(-1) N had the largest biomass of young root and the lowest shoot-root ratios. Leaf extension rate was lo w in the 1 mg l(-1) N treatment. Plants given 10 mg l(-1) N had the greates t proportion of green shoot material but little root growth; while those at 100 mg l(-1) N produced ver little shoot and root biomass. Preferential as similation of NH4+-N and a low N requirement make Whitegrass well adapted t o dominating vegetation on much of the Falkland Islands.