A Dynamic programming Model is used to select the most profitable crop rotation from seven crop alternatives including pasture. Crop yields within a rotation are estimated by specifying growing season rainfall, water use efficiency and weed and disease penalties caused by the three previous years crop history. A provision exists to include the effect on yield of other natural resource limitations. Regional variations can be accounted for by varying rainfall, management practices, yield penalties and input costs. A nitrogen-phosphorous calculator ensures sufficient fertiliser is applied for the crop to achieve its expected yield. This approach can be used to measure the productivity implications of advances in technology as well as the impact of rainfall, yield and price variations on optimal rotations.