Global: Two-Year Potato Rotations Lost About One-Third of Yield in a 12-Year Canadian Trial
In a Manitoba rotation trial, potato-canola yielded 95 cwt/acre less than three- and four-year rotations, and vascular wilt hit most plants. Other studies show the break crop also changes yield.
How often can potatoes return to the same field? A long-term rotation study near Carberry, Manitoba, in Canada gives one of the clearest answers. Scientists from Agriculture and Agri-Food Canada and the University of Manitoba started it in 1998 at the Canada-Manitoba Crop Diversification Centre, under irrigation, and ran it to 2009.
Two years versus three or four
The trial compared six rotations: potato-canola, potato-wheat, potato-canola-wheat, potato-oat-wheat, potato-wheat-canola-wheat and potato-canola followed by two years of alfalfa. According to the study team’s paper, in 2007 the marketable yield in the potato-canola rotation averaged 263 cwt per acre. This was 95 cwt per acre less than the average of the three- and four-year rotations. In metric terms, that is about 29.5 t/ha against 40.1 t/ha (our calculation).
Disease explained much of the gap. In 2007, more than 75% of plants in the potato-canola rotation had vascular wilt, against 18% in potato-wheat. Top Crop Manager reported that by 2009 the two-year rotations gave only about two-thirds of the yield of the longer rotations for tubers of at least 5 cm. In that year, 99% of plants surveyed in the potato-canola rotation showed vascular wilt. The researchers concluded that two-year rotations are probably not sustainable in Manitoba in the long term.
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The crop before potatoes also counts
Length is not the only factor. In Atlantic Canada, a study in the American Journal of Potato Research (2022) compared two three-year rotations. Potato-soybean-barley gave an average of 46.2 t/ha, against 38.6 t/ha for potato-barley-red clover, a gain of 19.5%. The response differed by variety: 36% for Gold Rush, 17% for Russet Burbank, 14% for Prospect and 3% for Shepody.
In Maine, USDA researchers Robert Larkin and John Halloran tested disease-suppressive rotation crops. According to the USDA ARS summary, a mustard blend used as green manure raised yield by 25% compared with a soybean control and cut black scurf by up to 54%. Net income rose by 600 to 780 US dollars per hectare.
Why it matters
Short rotations save land in the short term but let soil diseases build up. In the Manitoba trial, the cost was about one-third of the yield. A rotation of at least three years, with a well-chosen break crop, protects both yield and quality. Farms that rent land for potatoes should check the field history before signing.
Photo: A flowering potato plant in a field (illustrative). Ezhuttukari / Wikimedia Commons, CC BY-SA 3.0
