Cropping systems have a larger impact on N2O emissions than rainfall extremes in Zimbabwe

Nitrous oxide (N₂O) emissions under maize-based cropping systems remain insufficiently quantified, especially in sub-Saharan Africa. Moreover, the impact of climate change on N₂O emissions is largely underexplored. Here, we monitored N₂O emissions during two years (2023-24, 2024-25) at an on-station rainfall manipulation field experiment in Zimbabwe. Three rainfall regimes are applied, reduced rainfall (-30%), ambient rainfall, and heavy rainfall (addition of 100 mm/day two times per year) and 7 cropping systems including maize, cowpea sole and maize-cowpea intercropping systems.

The experiment was established as a split-plot trial with three replicates on a Rhodic Ferralsol. N₂O fluxes were measured repeatedly using static chambers alongside soil water-filled pore space, temperature, and mineral nitrogen. Cumulative and yield-scaled N₂O emissions were calculated.

Heavy rainfall significantly increased cumulative emissions (2.80 kg N₂O–N ha⁻¹ yr⁻¹), while reduced and ambient rainfall resulted in lower emissions (1.98 and 1.97 kg N₂O–N ha⁻¹ yr⁻¹, respectively). Sole cowpea had the highest cumulative emissions (3.29 kg N₂O–N ha⁻¹ yr⁻¹). Intercropping systems at full density with full N fertilization and half density with half N fertilization (2.96 and 2.48 kg N₂O–N ha⁻¹ yr⁻¹, respectively) were similar to fully fertilized sole maize (2.72 kg N₂O–N ha⁻¹ yr⁻¹), but emitted more than non-fertilized sole maize (1.03 kg N₂O–N ha⁻¹ yr⁻¹) and mulched sole maize with or without fertilization (2.06 and 1.21 kg N₂O–N ha⁻¹ yr⁻¹). These results highlight that rainfall extremes influence N₂O emissions, yet crop and nutrient management remain critical for mitigating emissions under increasing climate variability.