A Model for Optimal Selection of Machinery Sizes within the Farm Machinery System

A systems model has been developed to support the process of choosing the optimal level of farm mechanisation in terms of technical capability. The optimisation model is a non-linear programming model implemented by using the programming software suite General Algebraic Modelling System (GAMS). It is based upon a least-cost concept involving all expected fixed and variable costs (including timeliness costs) for a particular farm size and crop plan. The output from the model is the sizing of each machine, and also the tractor power and number of tractors required. The effective work rates of the machinery sets and the duration in nominal time for performing each operation are also shown. The selection is based upon a farm-oriented matrix involving various types of constraints, such as available man-hours, available machine- and tractor-hours, timeliness and workability of operations, agronomic window of operations, and sequence of operations. The model was tested and verified for its operational behaviour using real farm data. Comparisons of the optimised machinery requirements with the actual machinery present on a case-study farm showed generally good agreement, although there were some significant differences, suggesting that some of the actual machines were not sized optimally.