Corn (Zea mays L.) grain yield is closely related to plant density and is typically maximized in the northern Corn Belt when planting occurs in late April. However, spring rainfall events oft en result in wet soil conditions that delay planting. From 2008 to 2010, experiments were conducted at two locations in southern Minnesota to determine whether the agronomic responses of corn to plant density diff er with planting date. Six plant densities ranging from 38,400 to 107,900 plants ha -1 were evaluated within three planting dates that occurred on 2-wk intervals beginning in late April to early May. Yield and net return to seed cost were not aff ected when planting was delayed 2 wk, but were 15 and 18 to 30% lower when planting was delayed 4 wk, respectively. Yield loss due to late planting was associated with a 7% decrease in kernel weight and no change in kernels per square meter. Responses to plant density for stalk diameter, intercepted photosynthetically active radiation (IPAR) and leaf area index (LAI) at silking, lodging, grain yield and components, and net return to seed cost for 25 economic scenarios did not diff er with planting date. Th ere was a quadratic-plateau response of grain yield to plant density with yield maximized at ≥81,700 plants ha -1 . Th ese results from a 102-d relative maturity hybrid over six site-years in southern Minnesota show that increased plant density may not be able to off set the yield and economic losses associated with late planting.

Increased corn (Zea mays L.) seed costs and hybrids with greater stress tolerance than in the past make it important to know if the optimum plant density for corn grain yield diff ers with hybrid relative maturity (RM) or row width. In 2009 and 2010 at two locations in southern Minnesota, agronomic responses of corn to plant densities ranging from 40,700 to 108,700 plants ha -1 were evaluated for 95-, 101-, and 105-d RM hybrids in 51-and 76-cm row widths. Stalk diameter, intercepted photosynthetically active radiation (IPAR) and leaf area index (LAI) at silking, root and stalk lodging, grain yield, and yield components did not diff er with row width, and the response of these variables to plant density was not aff ected by hybrid or row width. Yield of the 105-d RM hybrid was 13% higher than that of the 95-d RM hybrid due to greater kernel number despite lower kernel weight, but was similar to the 101-d RM hybrid. Th ere was a quadratic-plateau response of grain yield to plant density, with the plateau occurring at 84,500 plants ha -1 . Net return was not aff ected by row width, hybrid, or 23 of 25 scenarios for seed cost and grain price. Th e economically optimum plant density was 62,200 plants ha -1 for US$350 per 80,000 seeds and US$120 Mg -1 , and 87,000 plants ha -1 for US$150 per 80,000 seeds and US$280 Mg -1 . Th ese results demonstrate that grain yield can be maximized with mid-and late-RM hybrids and plant densities ≥84,500 plants ha -1 in either 51-or 76-cm rows.

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Soybean [Glycine max (L.) Merr.] physiological characterization in a maximum yield environment may identify yield‐optimization factors, lead to reassessment of fundamental crop model parameters, and provide guidance for management or breeding efforts. From 2011 to 2013, we characterized biomass and N accumulation rates, radiation use efficiency (RUE), and yield for four or five cultivars in a maximum‐yield contest field. Grain yield among cultivars ranged from 5290 to 7953 kg ha−1. The highest yields were observed in 2013, when biomass and N accumulation rates ranged from 45.6 to 64.3 g m−2 d−1 and 1.43 to 2.08 g N m−2 d−1, respectively, and when RUE values ranged from 1.46 to 1.89 g MJ−1. The observed crop growth characteristics in 2013 were near or above the maximum values previously reported in the literature. These empirical measurements provide collateral data documenting a soybean crop with grain yields approximately 6719 kg ha−1.

• An understanding of the main factors influencing grain yield in soybean can provide key insights for making management decisions to increase yield. • Seed number is determined by the amount of photosynthate produced between R1 and R5 that is allocated to the seeds, divided by the minimum amount of photosynthate needed to keep a single seed from aborting. • Stresses or improvements in crop growth prior to flowering should not have a significant impact on final yield, provided that >95% light interception is achieved by R1. • Seed weight is determined by the seed growth rate and the length of the seed fill period. • Simplified, soybean yield is mainly determined by photosynthate production from R1 to R5 and the length of the seed fill period. • Management practices should focus on maximizing photosynthate production during seed set to increase seed number and limiting stresses during seed fill to extend the seed fill duration and increase seed weight.