Comparison of winter-active phalaris with the Australian cultivar under rotational grazing .1. Basal area and plant density

Basal area and plant density in fixed quadrats are presented from a grazing trial comparing the persistence of 2 'winter-active' cultivars (Sirosa, Holdfast) and a breeding population (Perla Retainer) of phalaris (Phalaris aquatica L.) possessing high seedling and winter growth rates with the original cultivar Australian. Four replicate pastures, 2 at each of 2 sites near Canberra, were grazed year-round at 15 wethers/ha for 3 years using a rotational system of management (2 weeks on, 4 weeks off). The first site, The Elms, was located on a slope with shallow, coarse-textured soil; the second, Boundary Creek, was level with deep soil which was very acid in the upper 20 cm. Both sites were fertilised with superphosphate and, except for small areas, were limed before sowing. Significant mortality was observed only at The Elms during the summer-autumn drought after grazing commenced, when plant death was highest for Australian and lowest for Perla Retainer, an erect, summer-dormant population. Basal area of Australian and Sirosa, but not Holdfast and Perla Retainer, subsequently recovered. Australian established and maintained a 50-70% higher basal area due to a 30-40% higher area per plant and 15-25% more plants. The cultivars did not differ markedly in persistence measured as stability of basal area. However, Perla Retainer showed less vegetative expansion at the first site after grazing commenced and was considered less persistent than the cultivars there. Persistence was correlated with the productivity of individual plots, all cultivars being affected similarly. Regressions which varied with cultivar were derived in which basal area at establishment, but not subsequent changes in basal area under grazing, was positively related to soil fertility factors, mainly phosphorus, potassium and manganese. An association between the initial basal area of Sirosa and soil magnesium levels was also detected at 1 site. It was concluded from this study, which was conducted in the absence of major drought, that the winter-active cultivars of phalaris can be as persistent as Australian under rotational grazing and with adequate soil fertility, but that interactions with site will occur.