Nitrous oxide (N2​O) is a potent greenhouse gas, and its emissions from agricultural practices are a significant concern globally. In sub-Saharan Africa (SSA), smallholder farming systems often face nutrient limitations due to minimal fertilizer use. Conservation Agriculture (CA), which includes crop rotation with legumes and the incorporation of biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More, is promoted to boost soil fertility and nitrogen (N) availability. However, the impact of these practices on N2​O emissions in unfertilized agroecosystems needs further investigation. A recent preprint by Talent Namatsheve, Vegard Martinsen, Jan Mulder, Alfred Obia, and Peter Dörsch, discusses a study conducted in a Ferralsol in northern Uganda to evaluate crop yield, soil N, and N2​O emissions in a pigeon pea-maize rotation system.

The study, spanning two consecutive cropping seasons (April-October 2023 and October 2023-January 2024), compared conventionally tilled systems (crop rotation vs. continuous maize monocropping) and different tillage systems (conventional, CA, and CA+biochar) under pigeon pea-maize rotation. CA was defined as reduced tillage with planting basins and crop residue retention, while conventional tillage involved overall ploughing.

The findings revealed that grain yield was not significantly affected by either crop rotation or tillage system across all treatments. N2​O fluxes were generally small, ranging from 1.02−51.19 μg N m−2h−1 over the entire study period. Short-lived N2​O emission peaks were observed following pigeon pea harvest in the crop rotation treatments, which were absent in maize monocropping. Overall, cumulative growing-season N2​O emissions over 279 days ranged from 0.44−1.11 kg N ha−1.

A significant finding was the impact of CA and biochar on yield-scaled emissions. In the first season, yield-scaled N2​O emissions were significantly smaller in CA systems with biochar compared to conventional tillage. Specifically, yield-scaled N2​O emissions ranged from 0.16−0.32 g N2​O−N kg−1 grain in the first season, and CA and CA+BC treatments showed a remarkable 50% reduction in yield-scaled N2​O emissions compared to conventional practices. This suggests that combining CA and biochar effectively minimizes emissions without negatively impacting pigeon pea productivity. The study concluded that N2​O emissions were not affected by conservation agriculture and biochar in these low-input systems, likely because microbial immobilization overrides the influence of biochar on mineral N availability. While the N2​O emission peaks were short-lived, this research indicates that residue management might have temporary effects on N2​O emissions in unfertilized systems.

Source: Namatsheve, T., Martinsen, V., Mulder, J., Obia, A., & Dörsch, P. (2025). Nitrous oxide emission from pigeon pea maize rotation in response to conservation agriculture and biochar amendments in a Ferralsol, northern Uganda. EGUsphere Preprint Repository