Crop rotation model for contract farming with constraints on similar profits

In China, investors have contracts with smallholder farmers to plant organic vegetable crops. The objective of the smallholder farmers is to maximize profits per unit of farm area, and minimize the differences in profits between farmers. Farmers' profits are a function of the crop rotation scheduling and the achieved prices. Here we propose an operational model that considers a crop rotation scheduling for an investor that offers contracts to many smallholder farmers. A heuristic algorithm was designed to identify the optimal rotation scheduling that would achieve both objectives of maximizing prices and minimizing the profit differences between smallholder farmers. Real data from a Chinese company was used to parameterize the model. Model results indicate that significant improvements in profits and farmers equality could be obtained if an optimal crop rotation scheduling would be used.