“…While earlier PD have been known to yield more, there is the expectation that too early of a PD increases risk due to killing frost or poor soil conditions (Anderson & Vasilas, ; De Bruin & Pedersen, ; De Bruin & Pedersen, ; Robinson, Conley, Volenec, & Santini, ). Our study was focused on a range from average to late planting dates, with the increasing climatic variability, frequent delays in planting are observed across Iowa and the US Midwest (Hamlet, Byun, Robeson, Widhalm, & Baldwin, ; Hatfield et al., ; Kistner et al., ). In four of the seven sites we found an optimum, and in these cases, the optimum was from 1 May to 20 May (DOY 120 to 140).…”