No‐Tillage Effects on Population Dynamics of Soybean Cyst Nematode1

Abstract The soybean [Glycine max (L.) Merr.] cyst nematode (Heterodera glycines Ichinohe) can cause significant reductions in soybean yield in Tennessee. ‘Forrest’ soybean was grown for 4 yr on a Lexington silt loam (Typic Paleudalf) in an experiment comparing soybean production, using six primary tillage methods: five conventional tillage methods (between‐row subsoiling, under‐row subsoiling, chisel plowing, moldboard plowing, and disking) and no‐tillage in chemically killed wheat (Triticum aestivum L.). In the fourth season, cyst numbers were lower in no‐tillage compared to conventional tillage. Race 3 and 4 were present in the experimental area. In the fifth season (1983), two cultivars, Forrest (Race 3 resistant) and ‘Bedford’ (Race 3 and Race 4 resistant), were used. Cyst numbers continued to be higher under conventional tillage with both cultivars. Tillage significantly affected soybean cyst nematode which affected the yield of Forrest but not Bedford. In 1983, yields of Bedford were significantly higher than those of Forrest under conventional tillage but not where the treatment had been no‐tillage for 5 yr. In the sixth season, yields were not significantly affected by tillage. Bedford yielded higher than Forrest across all treatments in the sixth year except in the continuous no‐tillage. In contrast to the fifth season, cyst numbers were lower at the end of the season where Bedford was grown. The two short‐term no‐tillage treatments [one in the previous soybean crop residue (2 yr) and one in wheat (1 yr)] were similar to conventional treatments in yield and cyst counts. Cyst numbers in the continuous 6‐yr no‐tillage were lower than the conventional or short‐term no‐tillage treatments.