Modelling the effects of sowing date and plant density on the yield and timing of development of Brussels sprouts (Brassica oleracea)

Abstract

SUMMARYThe effect of sowing date and plant density are modelled in relation to three variables: Ym, the maximum yield the crop can produce; τ, the interval from sowing to Yb/Ym = 0·5 where Yb is the yield of Brussels sprout buttons and Nb, the number of buttons on a plant stem. Ym is well related to the quantity of solar energy which the crop intercepts during the main period of growth. The fraction of radiation intercepted by the crop canopy is related to leaf area index (L) and sub-models relate L to sowing date and plant density. An empirically derived parameter relates the value of τ to thermal time and photoperiod time. The time course of Nb is modelled relative to the number of buttons at the end of the growing season. To overcome influence of site, variety and season, a generalized equation relates Nb, to plant density and a ‘known’ number of buttons at a specified planting density. The yield of buttons in specific size ranges (required for marketing) is described by a normal distribution with the standard deviation (σ) representing the spread of button diameter. There were no obvious effects of sowing date and plant density on σ. The model enables the effects of sowing date and plant density to be simulated using only simple and easily understood parameters. A sample simulation is presented.