IMPROVEMENT OF DRY TROPICAL RANGELANDS ON HAINAN ISLAND, CHINA - 4 - EFFECT OF SEEDBED ON PASTURE ESTABLISHMENT

Seedbed requirements for the establishment of grasses and legumes were studied in 3 experiments conducted over 3 years (1981-83) on the sand y (< 5 mg kg(-1) Bray P) and loam (> 20 mg kg(-1) Bray P) ultisol soil s found in the dry tropical rangelands of western Hainan Island, China Density at the end of the wet season and production accumulated over the growing season (May-October) were the discriminative parameters us ed. Experiment 1 measured the effect of seedbed preparation (cultivate d and uncultivated but heavily grass pasture) on the establishment of 2 grasses, buffel (Cenchrus ciliaris L. cv. Bilo-ela) and sabi (Urochl oa mosambicensis (Hack.) Dandy cv. Nixon), sewn alone or mixed with 3 styles (Stylosanthes guianensis (Aubl.) Sw. var. guianensis cv, Graham , S. hamata (L.) Taub. cv. Verano and S. scabra Vog. cv. Seca) on the 2 soil types. Bilo-ela buffel established better and produced more in subsequent years than Nixon sabi grass when sown on a cultivated seedb ed, but neither grass established when sown into undisturbed grassland . Companion styles established on both seedbeds, but initial density a nd yield was lower on the uncultivated seedbed. However, in 3-year-old swards, style yield on uncultivated seedbeds equalled or exceeded yie ld on cultivated seedbeds. Seca was the most productive style, but Gra ham yielded more consistently between years. Soil type had no effect o n sown grass production, but legumes grew better on the sandy soil. Ex periment 2 measured the effect of 4 seedbeds (heavily grazed, 1 diskin g, sprayed with herbicide, and cultivated to fine tilth) on establishm ent on Verano and Seca styles on sandy soil Density of both styles was highest where grass competition was minimized with herbicide and lowe st where heavy grazing was imposed prior to seeding. Compared to herbi cide, disking resulted in lower density and yield in the establishment yea, but the difference disappeared with time. Burial of seed too dee ply and subsequent competition from native species account for the poo r performance of both styles when drilled into a cultivated seedbed wh ich was still evident in 3-year-old swards. Experiment 3 examined the interaction between seedbed type (heavily grazed, burnt, 1 dishing, sp rayed with herbicide) and superphosphate application. Superior establi shment was measured on herbicide and disked treatments and production was still higher in 3-year-old swards than heavy grazing. Burning was more effective than heavy grazing. Increasing fertilizer input improve d legume production on all seedbeds, but did not affect density, Reduc tion in legume yield between 2- and 3-year-old swards in the burnt and disked treatment due to grass competition highlights the need for app ropriate grazing to maintain legume content of augmented grasslands, O verall we recommend rough dishing as the most practical and cost-effec tive means to augment native grasslands with styles. A fine seedbed is recommended to provide the disturbance required to establish grasses. There is no advantage gained by including grasses with legumes overse wn into living grassland.