Effects of defoliation and nutrients on growthPoa trivialisL. with perennial ryegrass

Abstract

For swards of Poa trivialis L. and Lolium perenne L. ‘Grasslands Ruanui’, in which P. trivialis contributed about 20% to harvested herbage yield in autumn, neither variation in frequency (17.8 cm or 7.6 cm height of herbage at cutting) or in intensity (5.t cm or 2.5 cm stubble after cutting) of defoliation prevented dominance of P. trivialis in winter. Although variation in intensity of defoliation affected subsequent rate of regrowth of the species contributing most to herbage yield in autumn and winter, ryegrass and P. trivialis respectively, rate of regrowth of the other species was not affected. P. trivialis dominance of ryegrass continued into spring until affected by dry weather. Nitrogen fertiliser applied at regular intervals from autumn to spring interacted with phosphorus fertiliser applied in autumn, so that at the higher rates of nitrogen, dry herbage yield from P. trivialis in winter increased more than that from ryegrass.