Grain yield and nitrogen cycling under conservation agriculture and biochar amendment in agroecosystems of sub-Saharan Africa. A meta-analysis

Summary

This meta-analysis synthesised 87 peer-reviewed studies (1643 paired observations) from 15 sub-Saharan African countries to evaluate how climate-smart agricultural practices—specifically conservation agriculture and biochar application—influence nitrogen cycling and grain productivity. Conservation agriculture and biochar significantly improved grain yield and nitrogen use efficiency compared to conventional practices, though residue retention increased both soil nitrate and nitrous oxide emissions. The effectiveness of these practices was modulated by soil organic carbon and total nitrogen content, with optimal grain yield observed in soils containing 0.5–1% total organic carbon, and biochar application particularly enhancing biological nitrogen fixation in nitrogen-rich soils.

UK applicability

The findings have limited direct applicability to UK conditions, as the meta-analysis focused specifically on sub-Saharan African agroecosystems with distinct soil, climate and agronomic contexts. However, the mechanistic insights on nitrogen cycling trade-offs under conservation agriculture and the role of soil carbon content may inform UK soil health policy and regenerative farming guidance, particularly regarding the management of crop residues to balance yield gains against greenhouse gas emissions.

Key measures

Grain yield; nitrogen use efficiency (NUE); soil nitrate-N (NO₃-N); nitrous oxide (N₂O) emissions; biological N₂-fixation; percent nitrogen derived from atmosphere (%Ndfa); total organic carbon (TOC) classes; total nitrogen (TN); response ratios

Outcomes reported

The study synthesised evidence on how conservation agriculture and biochar application affect soil nitrogen dynamics, nitrous oxide emissions, biological nitrogen fixation, grain yield and nitrogen use efficiency across sub-Saharan African agroecosystems. It examined how soil properties and regional factors modulate these responses and investigated interactions with inorganic nitrogen fertiliser use.

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