Establishment of introduced grasses at different stages of pasture development: effects of seedbed

Abstract

The seedbed preparation necessary for the successful establishment of five promising perennial grasses for the dry tropics was studied on two pastures - native grassland and a pasture dominated by Stylosanthes hamata cv. Verano - near Townsville, in northern Queensland. Seed of Cenchrus ciliaris cv. Biloela, Chloris gayana cv. Callide, Chrysopogon sp. CPI 5221 3, Digitaria milanjiana CPI 5981 4 and Urochloa mosambicensis CPI 46876 was sown into the two pastures, which had been left untreated, sprayed with herbicide, burnt, or burnt and cultivated. S. hamata cv. Verano was also sown on the native grassland plots. Sowings were made at the start of the growing season in successive years. Germination of all lines was adequate except where a thick layer of green and dead herbage physically separated the seed from the soil surface; this happened on the native pasture plots that were untreated or herbicide treated. However, there was high plant mortality in the first month after sowing except where plant competition had been reduced or removed by cultivation or spraying. After this period, most plants survived to the end of the wet season in both pasture types. This pattern of change in plant numbers resulted in good establishment on the cultivated seedbeds, some establishment on the herbicide-treated plots and little or no establishment on the control and burnt plots. Of the five grasses, U. mosambicensis had the best establishment and Chrysopogon sp. and D. milanjiana the worst. None seem likely to survive when sown into living grassland. We therefore conclude that the use of these introduced species will be largely restricted to completely cleared and cultivated land.