Effect of N fertiliser amount and water management on CO2 exchange and net ecosystem C balance of rice cultivation in southern Benin
Coffi Leonce Geoffroy Sossa1, Jesse B. Naab2, Juergen Augustin3, Souleymane Sanogo4, O. Luc Sintondji5, Mathias Hoffmann3
1West African Science Service Center on Climate Change and Adapted Land Use (WASCAL), Climate change and Agriculture, Benin
Application of mineral nitrogen (N) fertiliser and water management are two very essential farming practices, used to optimise potential yields in sub-Sahara African rice cultivation. Differences in both practices, however, might affect the patterns of climate relevant gaseous carbon (C) emissions (CO2 and CH4) and soil C losses, thus contributing to global climate change. To date, knowledge about the combined effects of different N fertiliser rates together with different water management practices on the gaseous C emissions and soil C losses are very limited. Our study aims to identify the best combination of water management and N fertiliser amount to reduce gaseous C emissions and limit soil C losses for an irrigated rice production in Benin. We hypothesise that especially a combination of alternate wetting and drying (AWD) as water management and an optimum amount of N fertiliser reduce gaseous C emissions and might help to enhance C sequestration by reducing soil C losses from irrigated rice production in Benin. To test this hypothesis, a field experiment was established at Koussin lélé, Cove district, southern Benin using a full factorial, split-plot experimental design. Within the experiment the combination of three levels of water management and two levels of N fertiliser amount are tested. The water management technologies include continuous flooding (CF) and two alternate wetting and drying (AWD) methods (AWD15 and AWD25) of irrigation. Nitrogen fertiliser levels is 90 kg/ha (farmer’s practice) and 120 kg/ha. To measure gaseous C emissions (CO2 and CH4) and estimate dynamics in soil C losses, an innovative, customized low cost dynamic NFT-NSS closed chamber system is used. The system consists of CO2/CH4 NDIR sensors connected to a microcontroller for data storage and transparent (NEE measurements) polycarbonate chambers (40 cm × 40 cm × 100 cm). To measure Reco, transparent chambers were covered with an opaque hood. Chamber measurements for diurnal variability in CH4 and CO2 fluxes are performed biweekly at all plots. In addition, agronomy and crop growth indices such as the Normalized difference vegetation index (NDVI) are measured weekly. Here we present CO2 and NECB balances for the first crop growth period.
Keywords: CO2 emission, N fertiliser, net ecosystem carbon balance (NECB), rice, water management
Contact Address: Coffi Leonce Geoffroy Sossa, West African Science Service Center on Climate Change and Adapted Land Use (WASCAL), Climate change and Agriculture, Carre121lotb/gbodje, 00229 Abomey-calavi, Benin, e-mail: sogeof1992gmail.com