Poster Session: Cropping Systems-Sustainability

475-P

Long-term crop rotations suppress soybean sudden death syndrome in Iowa.
N. ABDELSAMAD (1), G. C. Mbofung (1), A. E. Robertson (1), M. Liebman (1), L. F. Leandro (1)
(1) Iowa State University, Ames, IA, U.S.A.

Sudden death syndrome (SDS) of soybean caused by Fusarium virguliforme is one of the most damaging diseases of soybean in the US. Management of SDS relies on selection of resistant varieties, cultural practices to improve soil drainage, and avoiding planting in cool, wet soils. The effectiveness of crop rotation for SDS management is not well understood. In this study, the effect of long-term crop rotations in reducing SDS was studied in 2010 and 2011, in a field trial established in Iowa since 2002. The trial included three rotation treatments: corn-soybean, corn-soybean-oat/red-clover, and corn-soybean-oat/alfalfa-alfalfa. SDS incidence and severity, root rot and root growth, yield, and F. virguliforme and soybean cyst nematode (SCN) populations in soil were assessed. In both years, the 2-year rotation showed greater (P<0.001) SDS incidence and severity, and lower yield, compared to the 3- and 4-year rotations. Roots from the 2-year rotation showed more severe rot and reduced growth (P<0.05) compared to the longer rotations. SCN populations did not differ among rotations. Quantification of F. virguliforme in soil using real-time PCR suggested a greater pathogen population in the 2-year rotation compared to the 3-year rotation, but the mechanisms behind the reduction in SDS need further clarification. These findings suggest that long-term crop rotations may offer an alternative management practice for reducing risk of SDS.