Diversifying with grain legumes amplifies carbon in management-sensitive soil organic carbon pools on smallholder farms

Summary

This six-year on-farm trial in central Malawi evaluated the impact of grain legume diversification on soil organic carbon pools in smallholder farming systems. The doubled-up legume rotation (intercropped pigeonpea and groundnut rotated with maize) demonstrated higher values in management-sensitive SOC pools compared to continuous maize, whilst a pigeonpea-maize rotation showed increased mineralizable carbon. The findings suggest that legume diversification amplifies faster-cycling carbon pools that respond more readily to management practices, despite no measurable changes in bulk SOC.

UK applicability

The findings have limited direct applicability to UK conditions, as the study addresses marginal soils and smallholder systems typical of sub-Saharan Africa rather than temperate, mechanised agriculture. However, the methodology for measuring management-sensitive SOC pools and the principle that legume integration enhances carbon cycling may inform UK soil health assessment and regenerative farming practices.

Key measures

Water-extractable organic carbon (WEOC), particulate organic matter carbon (POM-C), potentially mineralizable carbon, macroaggregate carbon, microaggregate carbon, bulk soil organic carbon, total nitrogen

Outcomes reported

The study measured soil organic carbon (SOC) in bulk soils and aggregate fractions, alongside faster-cycling SOC pools including water-extractable organic carbon, particulate organic matter carbon, potentially mineralizable carbon, and macroaggregate carbon across different cropping systems. Treatment differences were found in management-sensitive SOC pools but not in bulk SOC or total nitrogen.

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