Yield-Based Corn Planting Date Recommendation Windows for Iowa

Core Ideas Three distinct site‐groupings resulted, with different recommended planting windows. Two planting windows were developed for each site‐grouping: 98–100% grain yield or 95–100% grain yield. The north‐central and northeast grouping had the earliest recommended planting window to maximize grain yield. Farmers use a suite of management practices to optimize corn (Zea mays L.) grain yield, including planting at appropriate times for their location. Research on planting dates across the years has tended to use categorical analysis and determination of recommendations by identifying a particular calendar date as optimum and setting yield decline relative to that. This approach was suitable given the experimental designs and number of sites available for analyses. An 18 site‐year Iowa dataset, however, that was constructed with planting dates on a sliding scale allowed regression analysis to be used instead of categorical analysis. This approach resulted in the construction of planting‐date recommendations as a window of time. Three distinct site‐groupings resulted for Iowa, which is different than previous statewide research: north‐central (NC) and northeast (NE); northwest (NW) and central (C); and southwest (SW) and southeast (SE). Two planting windows were developed for each site‐group based on the maximum yield on the response curve and a subtraction of 2 or 5% relative yield to develop yield windows of 98–100% or 95–100%, respectively. The response curves for each site‐grouping identify locations that exhibit a stronger grain‐yield response to planting date, especially in the northern and southern locations. The NC–NE grouping had the earliest 98–100% planting window (12–30 April) whereas the NW–C grouping (15 April–9 May) and SW–SE grouping (17 April–8 May) were later.