Neither chemical nor mechanical termination methods impact decomposition of late‐killed mature cereal rye

Abstract Agroecosystem benefits provided by a winter cover crop are proportional to residue quantity and decomposition rate. For growers who plant cover crops to suppress weeds and conserve soil moisture during the cash crop growing season, it is important to understand how management decisions such as termination method impact cover crop residue quantity and quality over time. A decomposition study was conducted in Maryland at two field sites with differing soil textures in 2022 and 2023 to test the impact of two broad‐spectrum herbicides frequently used for cover crop termination before cash crop planting. At anthesis, cereal rye ( Secale cereale L.) plots were either mechanically terminated with a roller‐crimper or left standing. One week later, chemical termination treatments (glyphosate and paraquat) were applied to half of both the rolled and standing plots. After plant death, samples of the terminated cereal rye biomass were placed in mesh litterbags, which were affixed to the soil surface between corn rows. The litterbags were then retrieved at 2, 4, 6, 8, and 12 weeks after chemical termination treatments were sprayed and at corn harvest. No differences in decomposition rates were observed when biomass loss was calculated by calendar date or by heat units. In some site‐years, roller‐crimped cereal rye had higher concentrations of lignin and holocellulose. No differences in residue chemistry between the chemical termination herbicides were detected. Residue of mature cereal rye terminated late in the spring will decompose slowly regardless of termination method, maintaining a persistent mulch during the cash crop season.