Both competitive and non-competitive processes may strongly influence the growth of plants in a multispecific community, though the latter, particularly in experimental studies, are often overlooked. A method of analysis, based on the principles of the de Wit model, is suggested which may enable . the factors involved in both competitive and non-competitive aspects of interference between species to be identified.

The experimental design and mathematical procedures of de Wit were applied to a study of the influence of potassium level on the growth in monocultures and mixtures of the tropical pasture species Setaria anceps cv. Nandi and Desmodium infortum cv. Greenleaf. When de Wit's approach was extended to include an analysis of nutrient uptake data in conjunction with the dry matter yield responses of the two species, the causal factors in both competitive and non-competitive interference were able to be identified. By this technique it was confirmed that, at a low level of potassium, the Setaria severely restricted the growth of the legume Desmodium by competing for potassium. The Setaria itself grew considerably better in mixtures than in monoculture, and at a high level of potassium did so without detriment to the associated legume. This latter was shown to be a non-competitive effect reflecting the partial independence of the two species with respect to their sources of nitrogen. ___________________ *Part I, Aust. J. Agric. Res., 25: 739 (1974).

Luurs, G. P., Hopsrne, G. nNo He.ll, R. 1976. Roadside For personal use only.

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