Operational planning in horticulture: Optimal space allocation in pot-plant nurseries using heuristic techniques

Abstract

At IMAG, in Wageningen, a Decision Support System (DSS) for glasshouse nurseries has been developed, called the IMAG Production Planning system (IPP). This system focuses first on a tactical planning level and enables the grower to design a production plan, which optimizes space and labour utilization in his greenhouse. This tactical production plan, however, still has to be translated to an operational level. One of the problems involved here is determining the exact location of the planned crops in the greenhouse in each period of the plan. A space allocation plan gives these exact locations. The choice of the locations can influence the amount of internal transport and labour (for example during the spacing operation) that will be required for realizing the production plan. Other space allocation criteria are the specifications prescribed by the production process of the crop. An automated, highly interactive system for space allocation planning on the operational level is being developed for use on a personal computer. This enables the grower to design and easily change a graphical allocation plan that consists of a space-time diagram and, for each period, a layout of the compartment with the allocated crops. Construction of a space allocation plan is a complex mathematical problem because of the large number of crops with variable space requirements during their production and because of the many factors that influence the quality of the space allocation plan. A number of traditional operational research techniques, such as linear programming and dynamic programming, were found to be inadequate to solve the problem, mainly because of the enormous calculation time required. Research has therefore concentrated on finding new heuristic techniques, that will deliver a good (but not necessarily optimal) space allocation plan. One of the heuristic techniques that seems promising is the Genetic Algorithm.