Summary
This two-site field study in tropical Brazil (Goiás and Mato Grosso) evaluated how cover crop mixtures and monoculture second-season systems affect soil carbon dynamics over 5–9 years of management following annual soybean. Cover crop mixtures, combining millet, showy rattlebox, ruzigrass and (at one site) pigeon pea, generated 6+ Mg C ha⁻¹ year⁻¹ of aboveground biomass, elevated soil biological activity by 40–50%, increased POM by 53%, and supported greater chemical diversity in soil organic matter than single-species or fallow systems. Structural equation modelling confirmed positive associations between aboveground biomass quantity, soil biological activity, and SOC stocks, suggesting that diversity and residue quality drive carbon accumulation in tropical soils.
Regional applicability
Whilst this research was conducted in tropical Brazil under distinct climate and soil conditions (rapid OM turnover, seasonal water limitation), the mechanistic findings on cover crop mixtures, biological activity and POM accumulation are potentially relevant to United Kingdom mixed and arable systems seeking to enhance soil carbon under cooler, higher-rainfall conditions. Transferability would depend on species suitability (many tropical species are unsuitable for UK climates) and validation in temperate field conditions, but the principle that diverse, high-biomass cover crop systems enhance both biological activity and carbon fractionation aligns with regenerative agriculture goals in the UK.
Key measures
SOC stocks (Mg C ha⁻¹ year⁻¹), POM and MAOM fractions, soil biological activity (enzyme activity or microbial respiration), aboveground biomass (Mg ha⁻¹ year⁻¹), organic functional groups via spectroscopy
Outcomes reported
The study measured soil organic carbon (SOC) stocks, particulate organic matter (POM), mineral-associated organic matter (MAOM), soil biological activity, and aboveground biomass across different second-season cropping systems in tropical agroecosystems. Cover crop mixtures increased POM by 53%, enhanced biological activity by 40–50%, and demonstrated greater linkage between aboveground biomass quantity and SOC accumulation.
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