Optimum plant population densities for lupin (Lupinus angustifolius L.) in the wheatbelt of Western Australia
1994
French, R.J. (Western Australian Dept. of Agriculture, Merredin. Dryland Research Inst.) | McCarthy, K. (Western Australian Dept. of Agriculture, Geraldton) | Smart, W.L. (Western Australian Dept. of Agriculture, Lake Grace)
Lupin (Lupinus angustifolius L.) seed yields at various plant population densities were studied in 33 separate experiments throughout the wheatbelt of Western Australia between 1987 and 1990. Two types of equation were fitted to each data set by nonlinear regression: 1 described an asymptotic response, the other a response where yield reached a maximum but declined at higher densities. The second type of equation was used to describe a data set if the residual mean square was significantly lower than for the asymptotic equation. In all, 122 individual responses were fitted, of these only 13 were not adequately described by the asymptotic model. Optimum density was chosen according to an economic criterion (when marginal revenue from an increase in plant population density equalled marginal cost). Optimum density ranged from 14 to 138 plants per sq m and was linearly related to yield potential, which we defined as either the asymptotic yield value, or the maximum yield for responses that did not approach an asymptote. Yield potential ranged from 0.13 to 4.1 t per ha. The relationship between optimum density and yield potential was the same for cvv. Danja, Gungurra, and Yorrel; for a reduced branching breeding line (75A-329); and on soils classified as good or poor for lupins. The relationship between optimum density and yield potential should be useful for lupins throughout the wheatbelt of Western Australia.
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