Grazing studies on the Guadalcanal Plains, Solomon Islands 3. Comparison of existing mixtures with koronivia (Brachiaria humidicola) and with natural pastures

Pastures of a mixture of Brachiaria mutica (para) and B. decumbens (signal) grown with Centrosema pubescens (centro) and Macroptilium atropurpureum cv. Siratro and grazed at three stocking rates 1.8, 2.7 and 3.6 animals/ha for 5 and 6 years of grazing were compared with B. humidicola cv. Tully (Koronivia) oversown with centro and siratro and grazed at 3.0, 3.6 and 4•5 animals/ha and native pastures of Themedaaustralis and Pennisetum polystachyon oversown with Stylosanthes guianensis cv. Schofield after burning, and grazed at 1.3, 2–0 and 2.7 animals/ha. All pastures were given 20 kg/ha of sulphur. The para and centro pasture gave the highest live-weight gain with 731 kg/ha/year when stocked at 3.6 animals/ha in 1979–80. and 592 kg/ha/year in 1980–1. Signal grass gave 621 and 493 kg/ha/year in 1979–80 and 1980–1 at 3.6 animals/ha. Koronivia grass gave similar production as signal: 639, 466 and 406 kg/ha/year at 3.6 animals/ha stocking rate from 1979 to 1982. On the natural pastures 1st year gains were high, 412 kg/ha/year at 2.7 animals/ha, but declined to 224 kg/ha/year at 2.0 animals/ha in year 2. In the para pastures, centro increased up to 50 %, while with signal it increased to 25 % of the botanical composition, owing to a decline in grass dry matter. In koronivia pastures, centro and siratro declined, inversely with stocking rate, and M. pudica increased in the high stocking rate. In the natural pastures T. triandra declined with increasing stocking, to 1 % at 2.7 animals/ha. P. polystachyon remained approximately stable. M. pudica became important as grazing increased, and weeds also increased. Para grass was high in N, P, S and Na. N was low in signal, koronivia and T. triandra while the concentration of Na (0.41%) was high in koronivia, but it was extremely low in signal and T. triandra (0.02%). The trials suggest that landholders could commence grazing of existing natural pastures for up to 2 years at about 2.0 animals/ha in the 1st year and 1.3 animals/ha in subsequent years to obtain 350 kg LWG/ha in year 1 and the 200 kg LWG/ha thereafter. With cultivated pastures much higher yield can be obtained using para plus centro on the low-lying areas, and signal plus centro plus siratro on non-flooded areas. Koronivia can be used in occasionally intensively stocked areas. All pastures require S fertilizer every 2 years