Tropical Grasslands (2001) Volume 35, 34–42

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

F.D. HU and R.J. JONES

CSIRO Tropical Agriculture, Davies Laboratory, Townsville, Queensland, Australia


In a replacement series pot experiment on a yellow podzolic/yellow earth intergrade soil, 4 legume-grass mixtures were grown at 5 legume:grass proportions, and 2 soil fertiliser levels, 0 or 10 kg/ha P. Grasses were Urochloa mosambicensis cv. Nixon and Bothriochloa pertusa cv. Bowen grown in factorial combination with Stylosanthes scabra cv. Seca and S. hamata cv. Verano. Plants were harvested 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 was, however, far more competitive than Seca with both grasses, and equally as 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 fertiliser treatment, grass species and legume species.
Yields of Verano were higher than those of Seca with both grasses, and Verano 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 root yield.
Yields of all legume mixtures with Nixon were higher than the pure stand yields and gave relative yield totals (RYTs) >1 as anticipated for legume-grass mixtures. However, mixtures with Verano-Bowen gave RYTs ≈ 1. In mixtures with Seca, Bowen gave RYTs > 1 at the 50 and 75% legume mixtures, especially on the fertilised soil.

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