By Yannick Mijnheer (the Netherlands)
Route optimization is an effective way to decrease soil compaction in agricultural fields. Important factors contributing to soil compaction are number of wheel passes, total weight of the working unit, and soil moisture content. This research aimed to determine an optimal route for capacitated agricultural operations over predefined field tracks given local differences in susceptibility to compaction (e.g. wet spots). In capacitated operations, the total weight of a working unit is variable, leading to a variable induced soil compaction. Together with known wet areas in a field, this creates room for route optimization. Route optimization is approached as a capacitated vehicle routing problem. Methods for generating weighted graphs representing an agricultural field and for calculating a (near-)optimal route through this graph were developed. The total cost of a route was calculated by a weighted sum objective function that expresses soil exposure to compaction in the unit weightmeters [m*kg]. The optimal route is the one with the lowest value of weightmeters. A Tabu search algorithm was implemented to heuristically search possible routes. The defined route optimization method found routes that were more optimal than the routes chosen by farmers, with far lower costs. Furthermore, in a small test field the Tabu search algorithm consistently found optimal solutions in 15.2% of the time of an exhaustive search method. In a follow-up study the suggested methods should be tested in practice, by planning near-optimal routes ahead of capacitated field operations. In the future, the proposed methods could be applied to farming machinery that work with GPS and predefined field tracks, to plan routes and thereby decrease induced soil compaction.
Keywords: Capacitated vehicle routing problem; graph theory; precision agriculture; soil compaction; Tabu search algorithm.