Effects of grazing management on Sirosa phalaris herbage mass and persistence in a predominantly summer rainfall environment

Herbage mass, plant frequency and basal cover data collected from September 1993 to August 1996 were used to compare the effects of various seasonal c losures with continuous grazing on the persistence of Sirosa phalaris (Phal aris aquatica cv; Sirosa) at 3 sites on the North West Slopes of New South Wales. Sites were on-farm and consisted of up to 10 treatments with 2 repli cates and treatments were initially imposed in 2 different years. Pastures were either newly sown (3 years old) and grazed by either sheep or cattle, or degraded (14 years old) and grazed by sheep. Drought conditions prevailed in 1994-95, confounding the interpretation of the importance of treatments that involved long periods of closure, since s ignificant effects could be attributed to both grazing exclusion and the ti ming of the closure in relation to plant phenology. However, across all sit es and years, fitted values for phalaris herbage' mass were generally signi ficantly higher than the continuously grazed control in only 2 treatments: spring closure (at 1 site) and an extended spring closure combined with an autumn closure (at all sites). At the end of these studies phalaris herbage mass in spring-autumn closures was 4-32 times higher than the control plot s. These results were confirmed by analysis of initial and final plant freq uency data. At all sites, no recruitment of Sirosa seedlings occurred in an y treatment. These data support the hypothesis that for increased persistence in a summe r rainfall environment Sirosa phalaris requires some form of grazing manage ment that involves the exclusion of grazing in the critical periods of spri ng and autumn.