IMPROVEMENT OF DRY TROPICAL RANGELANDS IN HAINAN ISLAND, CHINA .1. EVALUATION OF PASTURE LEGUMES

During 1981-83, we studied some legumes for potential improvement of dry tropical (1,001 mm annual rainfall) rangelands in Hainan Island, China. The productivity and persistence of 16 pasture legumes were tested on sandy (<5 mg/kg available P) and loam (12-25 mg/kg) soils under cutting in a randomized block design with plots split for sequential sowings in 1981, 1982, and 1983. Dry matter yield, sward composition, and legume density were measured at the end of the wet and dry seasons each year. Thirteen legumes established with density averaged over 3 sequential sowings >1 plant/m2 on 1 or both soils, but only 5 perennial stylos (Stylosanthes), siratro [Macroptilium atropurpureum (D.C.) Urban], and centro (Centrosema pubescens Benth) (loam soil only) persisted through 2 dry seasons and yielded more than 0.5 metric tonne(t)/ha in 3-year-old swards.S. guianensis (Aubl.) Sw. cv Cook yielded best on both soils, but proved less tolerant to fire than cv Graham, which is the common stylo recommended by this study as a companion for Siratro for improvement of loam soil rangeland. Siratro was the only non-stylo to produce >2 t/ha and show relative stability with sward age, but careful grazing management and regular fertilization are needed to maintain siratro content above 40% in commercial sowings. Tolerance to fire, low P requirement, and high yield in 2- and 3-year-old stands makes S. scabra Vog. cv Seca the most suitable legume for sandy soil, but since it is slow to establish, a mixture of S. scabra and S. hamata (L.) Taub. cv Verano which is noted for its quick establishment and prolific seed production is recommended for range improvement of low P soils.