Shifting focus from external to in situ organic resources – The redesign of four tropical long-term experiments

Summary

This paper describes the redesign of four long-term field experiments in Kenya that had to be fundamentally restructured after approximately 20 years when previous treatments combining external organic inputs with mineral nitrogen failed to maintain soil organic carbon levels. The experiments now focus on regenerative cropping strategies that shift emphasis from external to in situ organic resources by increasing root biomass through maize-legume rotations, intercropping, and relay systems, evaluated across four distinct pedoclimatic conditions. This redesign reflects how scientific knowledge advancement and evolving agricultural challenges necessitate periodic revision of long-term experimental objectives to maintain research relevance and rigour.

Regional applicability

The pedoclimatic conditions and cropping systems studied (maize-based production in tropical Kenya) differ substantially from UK temperate arable systems. However, the methodological approach to redesigning long-term experiments and the principle of shifting from external to in situ organic resource management may inform UK regenerative farming research priorities and experimental design.

Key measures

Soil organic carbon (SOC) levels, maize crop yields, effectiveness of different cropping system treatments (maize-legume rotation, maize-legume intercropping, relay intercropping) in rebuilding SOC across different soil degradation levels

Outcomes reported

The study reports on the redesign process and new experimental treatments of four long-term field experiments across different pedoclimatic zones in Kenya. The experiments now evaluate the effectiveness of maize-legume rotation, maize-legume intercropping, and relay intercropping with forage grass in rebuilding soil organic carbon and increasing crop yields from degraded soil baselines.

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