The effect of plant density on calabrese head growth and its use in a predictive model

Abstract

Three experiments studied the effect of plant densities between 5 and 40 plants m-2 on the head development of cvs Skiff and Cruiser. The time of head initiation and the final number of leaves produced were not affected by plant density. In every experiment head diameter and head weight decreased and were more variable at higher densities. Quadratic relationships of the type y =ax2 + bx + c between In head diameter (y) and accumulated effective day-degrees (EDD) (x) accounted for up to 98.8% of the variance in In head diameter with independent a, b and c parameters. When c was constrained to the head diameter at initiation, the fit was not improved by varying a with density whereas there was an improvement in fit by changing b according to density. A linear relationship between b and plant density was used to adjust the value of b in previously determined models of head growth. These adjusted models were then applied to independent crops. The accuracy of predictions of the time when these crops produced heads of specified diameter was tested using the head diameters of early crop samples as a starting point. Predictions were very accurate when using actual head diameters and observed weather but were less accurate when using target diameters and average weather.