Cereal rye seeding rate effects on residue quality and following soybean performance

Abstract

Cereal rye (CR; Secale cereale L.) is widely used as a winter cover crop in soybean ( Glycine max L.) production systems to reduce soil erosion and capture residual soil nitrogen (N). However, soybean responses to CR residue depend on biomass quantity and residue quality, both of which are strongly influenced by CR seeding rate. To evaluate the effects of CR seeding rate on biomass production, residue carbon (C) and N dynamics, and subsequent soybean performance, a two-year field experiment was conducted during the 2022–2023 and 2023–2024 growing seasons in southern Illinois. This study was arranged in a randomized complete block design with four replications and included a no-cover crop control and four CR seeding rates (14, 28, 42, and 56 kg ha ⁻¹ ). CR biomass increased linearly with increasing seeding rate across years, whereas C accumulation showed a significant year × seeding rate interaction, increasing linearly with seeding rate in 2024 but not in 2023, while tissue N concentration declined with increasing seeding rate across years and residue C:N ratio increased in both years, with a stronger response in 2024. Soybean biological yield was not affected by CR seeding rate; however, soybean grain yield remained stable at low to moderate seeding rates (14–42 kg ha ⁻¹ ) and declined at the highest rate (56 kg ha ⁻¹ ). Yield reductions at high seeding rates were driven primarily by decreases in seed number and harvest index. Principal component analysis showed that seeding rate was the dominant driver of CR biomass and residue quality, whereas environmental conditions explained most year-to-year variation. Economic analysis indicated that net returns were maximized at moderate seeding rates, particularly at the minimum financial incentive-eligible rate of 34 kg ha ⁻¹ . These results suggest that moderate CR seeding rates can optimize residue benefits while maintaining soybean yield and profitability.