Emissions of carbon dioxide, methane and nitrous oxide from soil receiving urban wastewater for maize (Zea mays L.) cultivation

We investigated how amending maize with wastewater at 120 kg N ha−1 affected crop growth, soil characteristics and emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) compared to plants fertilized with urea. Maize growth response was similar when fertilized with urea or wastewater despite a delayed release of nutrients upon mineralization of the organic material in the wastewater. Applying wastewater to soil significantly increased the mean CO2 emission rate 2.4 times to 1.74 µg C kg−1 soil h−1 compared to the unamended soil (0.74 µg C kg−1 soil h−1), and cultivating maize further increased it 3.2 times (5.61 µg C kg−1 soil h−1). Irrigating soil with wastewater, cultivating it with maize or applying urea had no significant effect on the emission of N2O compared to the unamended soil (1.49 × 10−3 µg N kg−1 soil h−1). Adding urea to soil did no affect the CH4 oxidation rate (0.1 × 10−3 µg C kg−1 soil h−1), nor did cultivating maize in the urea-amended soil, but adding wastewater to soil resulted in a significant production of CH4 (128.4 × 10−3 µg C kg−1 soil h−1). Irrigating soil with wastewater increased the global warming potential (GWP) 2.5 fold compared to the urea amended soil, while in soil cultivated with maize GWP increased 1.4 times. It was found that irrigating crops with wastewater might limit the use of N fertilizer and water from aquifers, but the amount applied should be limited because nitrate (NO3−) leaching and emissions of CO2, N2O and CH4 will be substantial and the increased soil salt content will limit crop growth.