F.E. MASSA1 and L. 't MANNETJE2
1Agricultural University, Wageningen, The Netherlands.
2CSIRO, Division of Tropical Crops and Pastures, St. Lucia, Brisbane. Qld. 4067.
Although Townsville stylo is persistent and contributes to animal production in this sub-coastal, subtropical region, it shows considerable year to year variation in plant numbers and pasture yield. This variability was examined by monitoring a Townsville stylo population in a spear grass (Heteropogon contortus) pasture, which had been oversown with Townsville stylo fertilised with superphosphate and continuously grazed.
The main findings were that (i) the pasture remained spear grass dominant, (ii) within a growing season there were several waves of germination originating from soil seed reserves, which had a high proportion of hardseededness, (iii) a large proportion of seedlings died particularly during dry periods with high temperatures and (iv) seed production was high. These findings were in contrast to the behaviour of similar pastures in seasonally dry tropical regions in northern Australia. There, perennial grasses were replaced by annuals and the level of hardseededness at the start of the growing season was much lower, resulting in one major germination wave. Some reasons for this difference in behaviour may be related to effect of temperature on breakdown of hardseededness of the Townsville stylo, mineralisation of soil nitrogen and grazing pressure resulting from severity of the long dry season.