Influence of grazing and herbicide before sowing on establishment and survival of surface sown pasture species on the Northern Tablelands of New South Wales

Abstract

The effect of surface sowing into different levels of native and naturalized vegetation, both herbicide treated and untreated, was evaluated in terms of seedling numbers and development at three sites on the Northern Tablelands of New South Wales during 1970-71. The herbicide mixture (2,2-DPA + Amitrole: 11.0 + 1.1 kg a.i./ha, respectively) was applied eight weeks before sowing with Trifolium subterraneum, Medicago sativa, Festuca arundinacea, Dactylis glomerata and Phalaris aquatics. Seedlings were counted 2, 6 and 11 months after sowing, and seedling development was assessed at the two initial samplings. Relative humidity and temperature 0.5 cm above ground level were measured with thermocouples for two months after sowing. Mean seedling numbers over all sites increased from 18.8 to 47.3; 5.2 to 30.2; and 5.5 to 12.1 /m2 for samplings 1,2 and 3, respectively, as level of vegetation increased. In particular, seedling numbers responded to height of vegetation rather than weight. Relative humidity increased and temperature decreased as vegetation height increased, but regressions of seedling numbers against relative humidity and temperature were not significant and indicated that vegetation height influenced seedling numbers by some means other than relative humidity and temperature. Application of herbicide to control the resident vegetation increased mean seedling numbers over sites for sampling times 1,2 and 3, from 30.8 to 36.4; 8.8 to 26.6; and 3.9 to 14.1 seedlings/m2, respectively, and also accelerated seedling development.