Effect of ultra-early, early, and normal soybean planting dates and rye cover crop on soybean grain yield

With changes to climate and crop insurance, earlier soybean [Glycine max (L.) Merr.] planting dates need to be investigated. Additionally, the use of a cover crop prior to soybean is promoted as a sustainable practice though little is known about cover crop and ultra-early soybean planting (prior to April 15). The objective was to evaluate soybean planting date and cereal rye (Secale cereale L.) cover crop termination timing on cover crop biomass, soybean plant population, and yield. The study was conducted in Northeast and West Central Ohio in 2021 and 2022. Treatments included three soybean planting dates (early April, late April, and late May) and three cover crop treatments (termination 1-2 weeks prior to planting or "early," termination at or after planting or "late," and no cover crop). Cover crop biomass increased as termination was delayed. Soybean planted in early April resulted in a yield reduction of 1.8 Mg ha(-1) when planted into a cover crop compared to the no cover crop control. However, when soybean was planted in late April, grain yield was not different among cover crop treatments. Yield reduction associated with early April planting with a cover crop was likely due to low soybean plant population, especially in Northeast Ohio, where plant population was <55,000 plants ha(-1) with a cover crop and >120,000 plants ha(-1) without a cover crop. To maximize yield, soybean should be planted by the end of April in Northeast Ohio. In West Central Ohio, soybean can be planted in early April without a cover crop.