Competition in pots between two tropical legumes (Stylosanthes hamata and S-scabra) and two tropical grasses (Urochloa mosambicensis and Bothriochloapertusa) at two phosphorus fertiliser levels

In a replacement series pot experiment on a yellow podzolic/yellow earth in tergrade soil, 4 legume-grass mixtures were grown at 5 legume:grass proport ions, and 2 soil fertiliser levels, 0 or 10 kg/ha P. Grasses were Urochloa mosambicensis Nixon and Bothriochloa. Bowen grown in factorial Combination with Stylosanthes scabra cv. Seca and S. hamata cv. Verano. Plants were har vested after 10 weeks of growth. From the measures of competition calculated (relative crowding coefficient and relative replacement rate), there was no suggestion that Bowen was more competitive toward legumes than was Nixon at either P treatment. Verano wa s. however, far more competitive than Seca with both grasses, and equally a s competitive as the grasses on this soil. Yield of tops in all pots with added P was increased by about 50%. However, the botanical composition of the mixtures was similar at the 2 fertiliser rates. Grass yields in mixtures were higher with Nixon than with Bowen. and higher with the less competitive Seca than with Verano. The grass yield was also affected by interactions (P <0.05) of legume:grass proportion with fertilis er treatment, grass species and legume species. Yields of Verano were higher than those of Seca with both grasses. and Vera no was more responsive to P. Root yields tended to follow top yields: Verano-Nixon = Seca-Nixon > Verano -Bowen > Seca-Bowen. In pure stands. both grasses had higher (34-40%) root yields with P fertiliser. However, there was no response to P in legume roo t yield. Yields of all legume mixtures with Nixon were higher than the pure stand yi elds and gave relative yield totals (RYTs) >1 as anticipated for legume-gra ss mixtures. However, mixtures with Verano-Bowen gave RYTs approximate to 1 . In mixtures with Seca, Bowen gave RYTs > 1 at the 50 and 75% legume mixtu res, especially on the fertilised soil.