Cover crops and deep‐soil C accumulation: What does research show after 10 years?

Summary

After 10 years of observation, winter rye cover crops increased soil organic carbon, oxidisable carbon, and particulate organic matter only in the upper 5 cm of irrigated no-till continuous corn systems in the U.S. Corn Belt. Late-terminated rye accumulated SOC at approximately 0.207 Mg C ha⁻¹ year⁻¹ and increased biomass to 2.247 Mg ha⁻¹ in irrigated conditions, compared with minimal gains in rainfed systems. The authors conclude that at least 2 Mg ha⁻¹ of cover crop biomass is required to increase SOC, and that winter rye cover crops produce minimal alterations to soil carbon in no-till continuous corn systems in high-carbon soils (>22 g C kg⁻¹), though potential exists in lower-fertility, eroded, or low-carbon soils.

UK applicability

The findings from the U.S. Corn Belt may have limited direct applicability to UK systems, as UK temperate soils often have different baseline carbon levels and climatic conditions; however, the threshold of 2 Mg ha⁻¹ cover crop biomass for meaningful SOC accumulation provides a quantitative benchmark relevant to UK winter cover cropping practice. The biomass constraints identified (particularly in rainfed conditions) align with observed challenges in UK-grown rye and other winter covers under variable rainfall.

Key measures

Soil organic carbon concentration (g kg⁻¹) and stock (Mg C ha⁻¹ year⁻¹), POX-C concentration, POM concentration, cover crop biomass (Mg ha⁻¹), soil depth profile (0–60 cm)

Outcomes reported

The study measured soil organic carbon (SOC), permanganate oxidisable carbon (POX-C), and particulate organic matter (POM) concentrations down to 60 cm depth under winter rye cover crops in rainfed and irrigated no-till continuous corn systems after 10 years. Cover crop effects on carbon accumulation were quantified by termination timing (early versus late/at planting).

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