Planting and In-Season Management for Maximum Soybean Yield.

Relative gains in seed yield of U.S. grown soybean has not kept pace with that of corn over the past two decades.  Our objectives were to identify management practices producers can readily implement for improved soybean yield.  In 2011 experiments were conducted at three Illinois locations; Mascoutah, Champaign, and Princeton.  Six factors with two levels each were arranged in a complete factorial (2⁶) and replicated four times in a split, split-plot design.  Main plots were planting date, sub-plots variety, and sub sub-plots combinations of; seed treatment, seeding rate, foliar pesticide, and nitrogen fertilizer.  Planting dates were either normal (early to mid May) or late (late May to early June) and varieties either short or full season. Seed treatment consisted of either untreated; or seed treated with fungicides (metalaxyl and trifloxystrobin), an insecticide (imidacloprid), and Rhizobium japonicum; and seeding rates of either 140 or 200 thousand seeds per acre.  Foliar pesticide consisted of either untreated or pyraclostrobin and esfenvalerate applied at R3; while nitrogen fertilizer was applied at R2 at 80lb N/acre, or no nitrogen was applied.  At two of the three locations (Champaign and Mascoutah) full-season varieties increased yield with normal compared to late planting, while short-season varieties did not.  At Princeton however; seed yield of both varieties increased with the normal planting date.  Yield increase to foliar pesticides interacted (p= 0.13) with planting date and varietal maturity at Champaign; with the numerically largest response occurring with the full-season variety and normal planting date.  While at Princeton yield increased with foliar pesticides at the normal planting date, but not at the later date (p= 0.003).  Similar observations were made for yield response to nitrogen fertilizer; either earlier planting (Princeton, p= 0.12), or the full-season variety planted at the earlier date (Champaign, p=0.05) resulted in a yield increase.