Tillage, Row Spacing, and Planting Date Effects on Soybean following Corn or Wheat

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Abstract
Tillage practices have changed rapidly in recent years to help reduce soil erosion associated with moldboard plowing. The effects of tillage practices on other management decisions in soybean [Glycine max (L.) Merr.] production is unclear. This study was designed to investigate the relationships between tillage, row spacing, and planting date on soybean performance in a corn (Zea mays L.)-soybean rotation at three locations and in a soybean-wheat (Triticum aestivum L.) rotation at one location. Tillage systems evaluated were fall moldboard plow, fall chisel plow, spring disk, ridge-till, till plant (no ridge), and no-till. Soybean was planted in 10- and 30-in. row spacings in early and late May from 1982 through 1985. Percent residue cover after planting ranged from 7 to 15% for moldboard plowing to 74 to 87% for the no-till system. With a few exceptions, little difference was observed in plant density among any of the tillage systems, although plants were slowest to emerge from the no-till system and fastest to emerge from the ridge-till system. Tillage did not consistently affect soybean yield and yield differences were small in most years. The early-planted soybean yield was equal to or higher than that planted later in all but one case. The yield advantage for 10-in. rows compared with 30-in. rows ranged from 8 to 14% when averaged over all tillage systems and both planting dates. Reduced tillage systems had less effect on soybean production than planting date or row spacing.