Mitigating Source Reduction: Soil Amendments Buffering Maize Yield Against Canopy Defoliation in a Rainfed Savannah Agroecology.

Abstract

Maize production in Sub-Saharan Africa is increasingly constrained by erratic rainfall and acute canopy defoliation driven by biotic threats such as the fall armyworm and other leaf mining pests. While optimising soil health through Integrated Soil Fertility Management (ISFM) is known to improve baseline yields, its capacity to buffer crops against compounded above-ground source reductions and climatic stress remains underexplored. This study evaluated the morphophysiological and yield responses of early-maturing maize to variable intensities of lower-canopy defoliation (0%, 50%, and 75% leaf stripping) under five soil nutrient management strategies (poultry manure, compost, NPK, liquid fertiliser, and unamended control) in the Guinea Savannah agroecology of Ghana. The 2024 field trial was subjected to severe terminal drought and elevated thermal stress immediately following the reproductive transition. Contrary to classical source-sink paradigms, targeted 50% defoliation triggered a physiological overcompensation rather than a yield penalty. When buffered by compost or NPK, the 50% stripping regime maximised grain yield (up to 2.5 t/ha) and achieved a Yield Stability Index (YSI) exceeding 1.20. This resilience was mechanistically driven by the elimination of parasitic carbon sinks and a critical reduction in transpirational water loss during the terminal drought. Furthermore, even under severe 75% defoliation, compost and NPK amendments maintained high Leaf Area Efficiency (LAE) and yielded significantly higher (1.8 t/ha) than fully intact, unamended control plants (0.7 t/ha), which suffered comprehensive physiological collapse. These findings validate that robust baseline soil fertility fundamentally uncouples maize from the devastating impacts of concurrent abiotic and defoliation-induced source reduction.