Tillage and crop sequence effects on Heterodera glycines and soybean yields

Conservation tillage has been increasingly used in the midwestern USA. Long-term effects of tillage practices on the soybean [Glycine max (L.) Merr.] cyst nematode (SCN), Heterodera glycines, and soybean yields in corn-soybean rotation were studied in two fields in Minnesota (USA). The experiments were arranged in a split-plot design with tillage treatments as main plots and crop sequences as subplots. Tillage treatments were no-tillage (NT) and conventional tillage (CT). The crop sequences were six (Waseca) or nine (New Richland) combinations of SCN-susceptible 'Sturdy', SCN-resistant 'Freeborn' ('PI 88788' resistance source) and 'Pioneer brand 9234' ('Peking' resistance source) soybean rotated annually with corn. Tillage did not affect SCN population density at New Richland and had only minimal and inconsistent effects on SCN at Waseca. However, CT resulted in up to 370 kg ha^-1 greater soybean yield than NT at Waseca. Growing SCN-resistant cultivars was effective in the corn-soybean rotation for managing SCN and minimizing yield loss to SCN. Resistant soybean not only reduced SCN population density and increased soybean yield in the year when it was grown, but also resulted in a smaller inoculum population density and increased yield of susceptible and resistant soybean in the following soybean years. Pioneer brand 9234 was more effective than Freeborn in reducing SCN population density and increasing soybean yield in the following years. This study confirmed that use of resistant cultivars is an effective tactic for SCN management, but tillage is not an option solely for managing SCN population in the northern climate and soil conditions.