Establishment and Survival of Pasture Grasses Surface-Sown Into Wheat Stubble in North-Western New South Wales.

Abstract

In four experiments near Walgett, New South Wales, between 1987 and 1990, the establishment and survival of Astrebla lappacea, Setaria incrassata, Panicurn coloraturn var. rnakarikariense and Cenchrus ciliaris were determined when surface-sown into low, reduced or heavy stubble just before or after harvesting wheat (November or December). Despite external deleterious factors affecting three experiments, grasses established in the first six months after sowing in all experiments unde; above average rainfall. Best establishment (8 to 31 plants/m2 in the 1990 experiment) occurred in response to 166 mm in 12 rain days over a 29 day period in December-January 1990-91, followed by 10 dry days and then a further 60 mm of rain in February; plants flowered by May and thus survived winter well. Under non-flood conditions (1987, 1988 and 1990 experiments) the order of magnitude of establishment was: C. ciliaris, A. lappacea > S. incrassata > P. coloraturn. Under flood conditions (1989 experiment) establishment of S. incrassata was highest and that of A. lappacca was lowest. In the 1987 and 1988 experiments full stubble (1.5 and 3.4 t/ha) did not improve the establishment of surface-sown grasses over that on low stubble (0.1 and 1.4 tlha). In the 1989 and 1990 experiments establishment was lower on full stubble (5 and 7 tlha) than on low stubble (0.1 and 0.1 tlha) owing to, respectively, flooding and competition from volunteer wheat. After the six months establishment period grass density declined over the two to five year survival period with plants self- thinning due to interspecific competition. Allowing mature plants to seed increased plant density due to seedling recruitment under favourable climatic conditions.