Lessons from the Carberry Potato Rotation Study

Rapid expansion of the processing potato industry has contributed to a significant increase in irrigated potato production in Manitoba. However, information is lacking regarding optimum rotations for local conditions. In 1998, a crop rotation study was initiated on a Wellwood silt loam near Carberry to identify crop rotations that optimized crop yield and quality while maintaining soil quality. In this ongoing study, treatments consist of two 2-year, two 3-year, and two 4-year rotations of potato-canola (PC), potato-wheat (PW), potato-canola-wheat (PCW), potato-oat-wheat (POW), potato-wheat-canola-wheat (PWCW), and potato-canola(underseeded to alfalfa)-alfalfa-alfalfa (PCAA). Crop yield and quality, diseases, weeds, soil parameters, economics and wireworms are assessed on an ongoing basis. This paper will focus on potato yield, select tuber quality factors, and select potato diseases. Differences among rotations have begun to emerge as the study has matured. While no single rotation consistently out-performed the other rotations in terms of potato yield, a descriptive grouping methodology developed by Francis and Kannenberg (1978) placed PC, PCAA and PCW in the higher-yielding group in terms of marketable (>2”) yield based on average yield for the period 1998 through 2006. Rotations predominated by cereals fell into the lower-yielding group for this period. While data collected during the initial nine years of the rotation study suggested greater potential for blackleg, rhizoctonia and vascular disease in potato in the 2year rotations, consistent effects on yield were not evident. In 2007, however, the PC rotation had a significantly lower total tuber yield (339 cwt/ac) than the other rotations (average of 424 cwt/ac). The yield of tubers >2” was also lower in the PC rotation than in the 3and 4-year rotations, but similar to the PW rotation. Disease assessments revealed that more than 75% of potato plants in the PC rotation were affected by vascular wilt and that the most severe symptoms were almost exclusively associated with that rotation, suggesting that disease may have contributed to reduced yields in 2007. The PW rotation showed the next highest level of vascular wilt at 18% of surveyed plants. These preliminary findings from 2007 suggest that 2-year rotations may not be sustainable in the longer-term due to increasing disease pressure. Monitoring of this study will continue for 12 cycles of the rotation, until 2009, to determine whether observed trends will continue in the longer term.