Use of weather uncertainty, compaction and timeliness in the selection of optimum machinery for autumn field work—A dynamic programme

Abstract

A dynamic programming model is described which determines the cost of autumn ploughing and drilling taking into account weather uncertainty, soil compaction and timeliness of sowing. Every day is potentially workable and sub-models calculate the probability of the soil state becoming drier or wetter for different weather regions and the cost of soil damage due to working on the soil. The farmer chooses to plough, drill or not work in order to minimize his expected overall cost, thus a damage cost which makes a day unworkable at the start of the season may not do so later. The model allows an economic comparison to be made of machinery with different compaction characteristics. For example, on a 200 ha winter wheat farm, two 90 kW tractors are optimum at three sites although the average workable days range from 33 to 56. A gantry system needs to work considerably faster than a 120 kW tractor to be profitable. A graph indicates for each soil state whether to plough, drill or not work each day.