Emission of CO₂ and N₂O from soil cultivated with common bean (Phaseolus vulgaris L.) fertilized with different N sources

Addition of different forms of nitrogen fertilizer to cultivated soil is known to affect carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions. In this study, the effect of urea, wastewater sludge and vermicompost on emissions of CO₂ and N₂O in soil cultivated with bean was investigated. Beans were cultivated in the greenhouse in three consecutive experiments, fertilized with or without wastewater sludge at two application rates (33 and 55 Mg fresh wastewater sludge ha^{- 1}, i.e. 48 and 80 kg N ha^{- 1} considering a N mineralization rate of 40%), vermicompost derived from the wastewater sludge (212 Mg ha^{- 1}, i.e. 80 kg N ha^{- 1}) or urea (170 kg ha^{- 1}, i.e. 80 kg N ha^{- 1}), while pH, electrolytic conductivity (EC), inorganic nitrogen and CO₂ and N₂O emissions were monitored. Vermicompost added to soil increased EC at onset of the experiment, but thereafter values were similar to the other treatments. Most of the NO₃^- was taken up by the plants, although some was leached from the upper to the lower soil layer. CO₂ emission was 375 C kg ha^{- 1} y^{- 1} in the unamended soil, 340 kg C ha^{- 1} y^{- 1} in the urea-amended soil and 839 kg ha^{- 1} y^{- 1} in the vermicompost-amended soil. N₂O emission was 2.92 kg N ha^{- 1} y^{- 1} in soil amended with 55 Mg wastewater sludge ha^{- 1}, but only 0.03 kg N ha^{- 1} y^{- 1} in the unamended soil. The emission of CO₂ was affected by the phenological stage of the plant while organic fertilizer increased the CO₂ and N₂O emission, and the yield per plant. Environmental and economic implications must to be considered to decide how many, how often and what kind of organic fertilizer could be used to increase yields, while limiting soil deterioration and greenhouse gas emissions.