Persistence of Phalaris aquatica in grazed pastures. 2. Regenerative bud and tiller development

Abstract

The summer survival, regeneration and tillering characteristics of phalaris (Phalaris aquatica cv. Australian) were examined in pastures using 4 grazing management systems in a grazing trial in south-western Victoria over 2 consecutive seasons. The grazing treatments tested covered a range of management intensities from a set-stocked with low phosphate input system to an intensive rotation with high phosphate. The soil fertility and grazing methods tested had no effect on the plant developmental characteristics measured in the field. The phalaris tiller population regenerated exclusively from dormant buds, as no vegetative tillers formed in the late spring/early summer survived through to the autumn break. On average, 3.7 regenerative buds were formed on each reproductive tiller. Half of these regenerative buds grew out in the field during the following growing season forming a new tiller. Of the new tillers formed, 71% produced at least 1 secondary tiller, with the average total number of secondary and higher tillers produced per new tiller being 4.5. Across both seasons, an average of 6.7% of the maximum vegetative tiller density became reproductive, and these reproductive tillers each contributed 3.7 buds to the population’s regenerative capacity in the following season. A simple model of bud development and tiller turnover showed that each regenerative bud at the start of the growing season was replaced by 0.54 buds at the start of the following season, indicating a substantial population decline. Reproductive tiller density was identified as a key limitation to phalaris persistence in this experiment. It is proposed that lowering grazing intensity during spring will increase the proportion of tillers that become reproductive and enhance phalaris persistence.