Impact of manure and mineral fertilizer management on rice growth and methane emissions in nutrient-deficient lowlands of Madagascar's highlands

In Madagascar, rice serves as a primary dietary staple, making the nation the second largest producer of rice on the African continent. However, rice production remains limited in fulfilling the needs of the entire population due to low soil nutrient availability. Conventional organic amendments and mineral fertilizers can enhance soil nutrients and rice growth but can also affect methane (CH₄) emissions from paddy rice soils. Potential CH₄ emissions from fertilizer management in tropical contexts are not well known. This study conducted two experiments to assess the impact of fertilizer management on CH₄ emissions and rice production: a pot experiment involving farmyard manure (FYM; 10 t ha⁻¹), NPK fertilizer (60 kg N: 60 kg P₂O₅: 60 kg K₂O kg ha⁻¹), and a control (no fertilizer); and a field experiment involving FYM (10 t ha⁻¹) and NPK fertilizer (60 kg N, 66 kg P₂O₅, and 48 kg K₂O ha⁻¹). In the pot experiment, the application of both FYM and NPK fertilizers resulted in significant increases in grain yield of 105.1 % and 187.1 %, alongside increases CH₄ emissions of 84.8 % and 71.0 %, respectively, compared to those in the control. The field experiment results partially aligned with those of the pot experiment, showing similar CH₄ emissions from NPK and FYM fertilizers. However, the yield increase for NPK fertilizer was lower in the field (5.7 %) than that for FYM fertilizer. These findings underscore the need for balanced nutrient management strategies to enhance rice productivity while mitigating greenhouse gas emissions, which are crucial for sustainable rice cultivation in Madagascar.