Farmers need a well planned crop scheduling program to maintain a regular supply of broccoli (Brassica oleracea L. var. italica Plenck) to domestic and export markets which extend from May to September for crops in south-east Queensland. However, irregular production, due to variable temperatures, is a constraint in the production and distribution systems for broccoli. Variable temperatures influence the rate of crop development, time of harvest and crop quality, thereby impacting on marketing commitments which specify the amount, quality and date of supply. Thus, prediction of crop ontogeny is important for crop scheduling and maintaining continuity of supply of broccoli. Two methods are being used to develop a model of phenological development in broccoli. The first method uses a time of sowing experiment which records crop ontogeny for wide range of cultivars and climatic conditions. This method provides a high level of precision in determination of phenological events but has potential problem such as the difficulty of extrapolation from a small scale experiment to commercial crops. The second method uses historical records from a broccoli farm which reflect crop phenological development under commercial practice over a period of three years. This method has the advantage of using a number of crop performance records obtained from a range of prevailing climates but lacks the precision of the first method. Once both models exist, they can be separately validated against the data used to develop the other model. Furthermore, the ongoing year-by-year expansion in farm records represents new validation data for either model. Our three-step approach should lead to a more robust and credible model for predicting crop ontogeny in broccoli and it could also be applicable to other crops
