CARBON DIOXIDE AND GASEOUS NITROGEN EMISSIONS FROM BIOCHAR-AMENDED SOILS UNDER WASTEWATER IRRIGATED URBAN VEGETABLE PRODUCTION OF BURKINA FASO AND GHANA

Abstract

To quantify carbon (C) and nitrogen (N) losses in soils of West African urban and peri-urban agri culture (UPA) we measured fluxes of CO2-C, N2O-N, and NH3-N from irrigated fields in Ouaga dougou, Burkina Faso, and Tamale, Ghana, under different fertilization and (waste-)water re gimes. Compared with the unamended control, application of fertilizers increased average cumu lative CO2-C emissions during eight cropping cycles in Ouagadougou by 103% and during seven cropping cycles in Tamale by 42%. Calculated total emissions measured across all cropping cycles reached 14 t C ha–1 in Ouagadougou, accounting for 73% of the C applied as organic fertilizer over a period of two years at this site, and 9 t C ha–1 in Tamale. Compared with un amended control plots, fertilizer application increased N2O-N emissions in Ouagadougou during different cropping cycles, ranging from 37 to 360%, while average NH3-N losses increased by 670%. Fertilizer application had no significant effects on N2O-N losses in Tamale. While waste water irrigation did not significantly enhance CO2-C emissions in Ouagadougou, average CO2-C emissions in Tamale were 71% (1.6 t C ha–1) higher on wastewater plots compared with those of the control (0.9 t C ha–1). However, no significant effects of wastewater on N2O-N and NH3-N emissions were observed at either location. Although biochar did not affect N2O-N and NH3-N losses, the addition of biochar could contribute to reducing CO2-C emissions from urban garden soils. When related to crop production, CO2-C emissions were higher on control than on fertilized plots, but this was not the case for absolute CO2-C emissions.