Methods of analysing yield from trials in which the produce is graded according to diameter

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Abstract
SUMMARY: A study was made of the relationship between yields in particular size grades of carrots and onions and the number of plants per unit area with a view to providing adjustments to yields for differences in plant densities. It is concluded that the relationship for individual small grades cannot be fitted consistently by a single mathematical equation but that estimates of yields in small grades are best obtained by fitting a common equation to the accumulated yield at the limits of the grade and obtaining the yield by difference. Eleven previously published equations which have been shown to fit the relationship between total yield and plant density for a number of crops are compared with one newly developed for graded produce. It was found that the latter,where y = yield/ha, ρ = number of plants/m2 and A, B and C are constants, generally leads to the best fits when a large range of densities is present, but it is argued that, for adjustment of yields for small differences in densities such as are obtained in variety trials, a simpler equation such as a second degree polynomial is equally effective.