The Journal of Agricultural Science


Adjusting for fertility and competition in variety trials

M. DURBAN a1, I. D. CURRIE a2c1 and R. A. KEMPTON a1
a1 Biomathematics and Statistics Scotland, The King's Buildings, Edinburgh, EH9 3JZ, UK
a2 Department of Actuarial Mathematics and Statistics, Heriot-Watt University, Edinburgh, EH14 4AS, UK


A joint model for plot yield in response to fertility trends and interplot competition is described. The model combines the mixed model representation of a cubic smoothing spline to model fertility and a regression model with auto-regressive terms to model competition. Estimation is based on a generalization of residual maximum likelihood. The methods were applied to a series of 70 sugar beet trials conducted by the Plant Breeding Institute, Cambridge, UK, and the results summarized.

(Received July 28 2000)

c1 To whom all correspondence should be addressed. Email:

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