RESIDUE MANAGEMENT AND MINIMUM TILLAGE SYSTEMS FOR SOYBEAN FOLLOWING WHEAT

The acceptance of no-till systems for soybean [Glycine,nax (L.) Merr.] production following winter wheat (Triticum aestivum L.) on fine-text ured soils in Ontario has been hampered by soybean yield reductions du e to unfavorable seedbed conditions. This research was conducted to id entify alternative tillage and residue management systems that will en hance emergence, growth, and yield of soybean following winter wheat. Seven tillage and residue management systems, comprising fall moldboar d plow, fall chisel plow, fall disk only, Pall zone-till, no-till, no- till (with wheat straw baled), and no-till (with wheat straw and stubb le removed), were evaluated following winter wheat on fine-textured so ils from 1994 to 1996 at six different sites near Centralia and Wyomin g in southwestern Ontario. Spring soil moisture was lower in the fall tillage treatments than in no-till with wheat residue, but moisture di fferences did not vary among fall tillage treatments. No-till seedbeds had the highest soil moisture contents, the lowest proportion of fine soil aggregates (<5 mm in diameter), and the greatest penetrometer re sistance. No-till soybean growth was delayed and yields were reduced a s the level of wheat residue left after planting increased. Soybean se ed yield was negatively correlated with surface residue cover, but pos itively correlated with soil aggregates <5 mm in diameter at all sites . Fall zone-till and fall disk systems generally improved in-row seedb ed conditions (higher fine soil aggregates and lower soil resistance), and increased seed yields by 5 to 29% relative to no-till treatments. Fall zone-till and fall tandem disk systems were the best conservatio n tillage alternatives to fall moldboard plowing.