ABSTRACT
Summary Four perennial ryegrass (Lolium perenne L,)-Poa annua L.-white clover (Trifolium repens L.) swards with herbage mass ranging from 500 to 1,700 kg organic matter (OM)/ha were established and maintained in as near a steady state as possible by continuous but variable stocking with sheep in order to study the influence of herbage mass on rates of herbage growth (G), senescence (S), and net production (NP), and on species balance. Estimates of G, S, and NP were derived from measurements on individual grass tillers and clover stolon growth sites. The mean contributions to total G were 54, 20, and 4 ( ± 1.6) kg dry matter (DM)/ha/day for ryegrass, Poa, and clover, respectively. The low clover growth rates were due to low population densities, and Poa had lower population densities and lower individual-tiller growth rates than ryegrass. The ratio of senescence to growth was 0.47:1, 0.32:1, and 0.11:1 for Poa, ryegrass, and clover, respectively. The combined species G increased with herbage mass in an asymptotic manner towards a maximum of 118 kg DM/ha/day, and S increased linearly from 17 kg/ha/day at 500 kg DM/ha to 41 kg at 1,700 kg OM/ha. NP increased rapidly to a predicted maximum of 70 kg DM/ha/day at 1,230 kg OM/ha and then declined slowly. The results of this experiment suggest that there is limited scope, within practicable limits, for improving rates of net herbage production in temperate swards by manipulation of the herbage mass maintained under continuous stocking management.
