The Use of a Mathematical Model for the Analysis of Manurial and Weather Effects on the Growth of Carrots

A model for the study of yearly and other variation in cropyields, based on a generalized form of the logistic equationof growth, was applied to three years' growth analysis dataon carrot crops from 16 plots of a long-term manurial experiment.In the ideal case, it is postulated that the growth in differentyears of carrot leaves or taproots on soil receiving a givenmanurial treatment could be described by a single curve if timein days was replaced by a scale based on one or more meteorologicalelements which affect relative growth-rates. The equation fitted the data on the growth of the leaves butnot that on the taproots. For leaf growth, the use of the sumsof solar radiation, day degrees or evaporation from an openwater surface did not give curves that fitted the growth databetter than those obtained with time in days. Yearly differencesin leaf (but not taproot) growth appeared to be related to correspondingdifferences in rainfall amounts, and it is suggested that ascale taking account of soil moisture tension might have givena better fit to the model. It appeared that whereas the relative leaf growth-rate was afunction of leaf but not taproot weight, relative taproot growth-ratewas a function of taproot weight and leaf weight. A furthermodel for the growth of carrots, based on this hypothesis isdescribed.