Improvement of dry tropical rangelands in Hainan Island, China. 2. Evaluation of pasture grasses

During 1981-83, we studied 19 grasses for potential improvement of dry tropical (1,001 mm annual rainfall) rangelands in Hainan Island, China. The productivity and persistence of the grasses were tested on sandy (< 5 mg/kg available P) and loam sods (12-25 mg/kg) under cutting in a randomized block design with plots split for sequential sowings in 1981, 1982, and 1983. Grass response to legume-fixed and nitrogen fertilizer was also assessed. Thirteen of the 19 grasses tested under cutting established satisfactorily (density > 5 plants/m2), but only 6 cultivars produced yields > 1.5 metric tonne (t)/ha. Melinis minutiflora Beauv., Brachiaria decumbens Stapf. and Chloris gayana Kunth. yielded more than 1.5 t/ha in 3-year-old swards on both soils, whereas Panicum maximum Jacq. and Setaria sphacelata (Schum.) Stapf. ex Massey only performed well on fertile loam soil. Grass establishment was superior on sandy soil, but plant density did not correlate well with production which was higher on red loam soil due to better waterholding capacity and nutrient status. Compatibility of these successful grasses with companion legumes was low with legumes contributing < 0.4 t/ha to total yield of 3-year-old M. minutiflora, B. decumbens and P. maximum swards, and having minimal effect on soil nitrogen. Nitrogen fertilizer (50 kg N/ha/yr) more than doubled grass production, but was profitable only where grass response exceeded grass/legume swards > 4 t/ha. S. sphacelata was the only grass to form a stable mixture with companion legumes. [Macroptilium atropurpurem (D.C.) Urban and Stylosanthes guianensis (Aubl.) Sw.], which yielded more than 1.1 t/ha in 3-year-old swards on loam soil. This combination was recommended for improvement of loam soil rangelands. It is concluded from this study that range improvement with perennial grasses is confined to fertile soils, while direct broadcast of Stylosanthes legumes only into grazed native pastures is the practice recommended for improvement of infertile sandy soil until persistent low P tolerant grasses are found for the dry tropics.