Robel Pole Method Can Estimate Cereal Rye Biomass to Optimize Termination Timing

Abstract

Fully realizing the benefits of cover crops and minimizing the yield penalty requires knowing when to terminate them. Cereal rye ( Secale cereale L.) is the dominant cover crop used in the Midwest US, and previous work has shown that corn ( Zea mays L.) yield penalties began to occur more frequently when cereal rye is at ∼1000 lb dry biomass ac ⁻¹ . However, farmers do not have an easy, reliable way of estimating when this biomass occurs without time‐consuming or destructive sampling. This study evaluates the effectiveness of the Robel pole method as a rapid, practical tool for estimating aboveground cereal rye biomass accumulation in Iowa, aiming to help farmers optimize cover crop termination timing. Over two growing seasons (2022–2023) and multiple field sites, we established strong correlations (< 0.0001) between biomass accumulation, crop obstruction height, and accumulated growing degree days (GDD). Cereal rye biomass accumulation was proportional to crop obstruction height, validating the Robel pole's utility as a non‐destructive, instantaneous assessment tool. Cereal rye biomass increased linearly with GDD after a threshold of 3222 GDD, reaching up to 2617 lb ac ^{− 1} near termination. The Robel pole method provided an easy‐to‐use proxy for biomass estimation, requiring neither temperature data nor planting dates, enabling quick decision‐making to balance environmental benefits while minimizing potential negative impacts on subsequent crops.