Observations on tillering in cultivars of phalaris under rotational grazing in a year with a summer–autumn drought

Abstract

Changes in tiller numbers, timing of stem elongation, and tiller survival under summer moisture stress were measured in phalaris (Phalaris aquatica L.) pastures rotationally grazed at 15 wethers/ha during a study of the survival and productivity of a semi-winter-dormant cultivar (Australian) compared with 3 winter-active cultivars (Sirosa, Holdfast, Perla Retainer). The semi-winter-dormant cultivar maintained higher tiller numbers per plant and per area than the 3 winter-active cultivars, was later in its reproductive stem development, and was capable of more new tillering early in spring, but could display higher rates of tiller death late in spring. Although stem elongation in Australian started later in 1990, it was no less synchronous than in the winter-active cultivars. However, Sirosa had a higher proportion of elongating tillers than Australian under very infrequent grazing in a supplementary experiment during 1991. Cultivars did not differ in the proportion of tillers that were decapitated during spring 1990.

Perla Retainer displayed higher summer dormancy after rainfall in January 1991 and new tillers of Perla Retainer and Holdfast survived subsequent drought better than tillers of Australian. However, regeneration of the tiller population of Australian after drought ended was enhanced by a slightly higher propensity for tillering during July–September 1991.

The results suggested that maintaining grazing pressure and frequency in late winter and early spring should enhance tiller survival and improve the resilience of phalaris to episodes of heavy spring grazing. Later reproductive development probably benefits grazing tolerance in semi-winter-dormant cultivars, but the value of selecting for this in winter-active phalaris is uncertain. In areas with harsh summers, higher summer dormancy is required for survival combined with a capacity for tiller survival should growth occur. However, unnecessarily high summer dormancy will reduce the growth of green herbage and, consequently, animal production.