Planting System and Weed Control Effects on Soybean Grown on Clay Soil

Dryland soybean [ Glycine max (L.) Merr.] production on clay soils in the Mississippi River alluvial flood plain (Delta) is economically marginal, and production inputs must be minimized to achieve economic feasibility. One scheme for reduction of inputs is stale seedbed planting. Three chemical weed control options (none, preemergence only, and post‐emergence only) were compared in both stale and tilled seedbeds on a Sharkey clay (very‐fine, montmorillonitic, thermic Vertic Haplaquept) in 1981 and 1982. Four soybean cultivars representing Maturity Groups V, VI, and VII were used. Yields from the two seedbed treatments with preemergence weed control were equal, but seed yield from the tilled seedbed treatment with no herbicide averaged 225 kg ha −1 greater than the stale seedbed treatment with comparable weed control. Percent weed cover was lowest both years in the tilled seedbed with postemergence weed control. Weed species present in the greatest abundance were prickly sida ( Sida spinosa L.), pitted morningglory ( Ipomoea lacunosa L.), and slender aster ( Aster exilis Ell.). An unfilled seedbed is a viable choice with effective weed management to enable producers to minimize tillage inputs and still maintain yield on clay soils.