Determining the optimum crop rotation program involves consideration of economics as well as the sustainability and environmental impact of the rotation. In an eight year study of potato rotations in Manitoba, Khakbuzan (et al. 2010) found that potatoes were far more profitable than any of the other crops used in the rotation (canola, cereals or forage crops) and therefore 2 year rotations (ex. potatoes/canola or potatoes/wheat) were more profitable than longer rotations. A 2 year canola/potato rotation proved to be the most profitable despite the fact that in most years the canola crop actually returned net negative revenues due to low yields. The reason this rotation was so highly profitable was that alternating potatoes with canola appeared to substantially increase potato yields. The study did not explore why the potato/canola rotation was so much more favourable to the productivity of the potato crop relative to the canola crop. While the shorter rotations did tend to maximize short-term economic gain the study noted that soil erosion and loss of soil organic matter was greater in the 2 year rotations than when potatoes were included less often in the rotation. Eventually this degradation of the field conditions would lead to a decline in productivity for all crops in the rotation.
Source : Khakbazan, Mohr, Volkmar, Tomasiewicz, Moulin, Derksen, Irvine, McLaren and Monreal (2010). Amer. J. Potato Res. 87:446-457.