ORIGINAL PAPER The effect of moisture on nitrous oxide emissions from soil and the N 2 O/(N 2 O+N 2 ) ratio under laboratory conditions E. Ciarlo & M. Conti & N. Bartoloni & G. Rubio Received: 25 May 2005 / Revised: 17 July 2006 / Accepted: 24 August 2006 / Published online: 7 November 2006 # Springer-Verlag 2006 Abstract Nitrous oxide (N 2 O) contributes to greenhouse effect; however, little information on the consequences of different moisture levels on N 2 O/(N 2 O+N 2 ) ratio is available. The aim of this work was to analyze the influence of different soil moisture values and thus of redox conditions on absolute and relative emissions of N 2 O and N 2 at intact soil cores from a Vertic Argiudoll. For this reason, the effect of water-filled porosity space (WFPS) values of soil cores of 40, 80,100, and 120% (the last one with a 2-cm surface water layer) was investigated. The greatest N 2 O emission occurred at 80% WFPS treatment where conditions were not reductive enough to allow the complete reduction to N 2 . The N 2 O/(N 2 O+N 2 ) ratio was lowest (0–0.051) under 120% WFPS and increased with decreasing soil moisture content. N 2 O/ (N 2 O+N 2 ) ratio values significantly correlated with soil Eh; redox conditions seemed to control the proportion of N gases emitted as N 2 O. N 2 O emissions did not correlate satisfactorily with N 2 O/(N 2 O+N 2 ) ratio values, whereas they were significantly explained by the amount of total N 2 O+N 2 emissions. Keywords Nitrogen emissions . Environmental impact . Dinitrogen . Redox potential Introduction Dinitrogen (N 2 ) gas is the end product of denitrification, and nitrous oxide (N 2 O) is the by-product with important harmful environmental consequences because of its contri- bution to greenhouse effect. In addition, N 2 O is the main source of stratospheric nitric oxide, which damages the ozone layer (Crutzen 1979). N 2 O is also produced by nitrification, but N 2 O emissions are considered to be more driven by reduction than by oxidation processes in soil (Bergsma et al. 2002). Tiedje (1988) suggested that in aerobic systems, oxygen availability is the main limiting factor of denitrification, whereas in anaerobic systems, NO 3 - availability may be limiting. Both soil redox status and oxygen diffusion are affected by soil moisture, but there are contradictory results in the literature. Dobbie and Smith (2003) found the greatest N 2 O fluxes from pasture soils at water-filled porosity space (WFPS) values higher than 60% when NO 3 - concentration was nonlimiting. However, Bøckman and Olfs (1998) proposed that N 2 O formation is greater when soil WFPS ranges between 40 and 80%. Marinho et al. (2004) found that the maximum N 2 O fluxes occurred several days after strong rain events, with significant correlation coefficients (r =0.84–0.94) between N 2 O emis- sions and precipitations during 1 week before measure- ments. Data of rice-based agricultural systems showed that N 2 O emissions were greatest at not continuously flooded fields (Xing and Zhu 1997). McSwiney et al. (2002) concluded that N 2 O production is greatest under conditions that are suboptimal for nitrifiers and denitrifiers. Biol Fertil Soils (2007) 43:675–681 DOI 10.1007/s00374-006-0147-9 E. Ciarlo (*) : M. Conti Cátedra de Edafología, Facultad de Agronomía de la Universidad de Buenos Aires (FAUBA), Av. San Martín 4453, Capital Federal, Argentina e-mail: ciarlo@agro.uba.ar N. Bartoloni Cátedra de Métodos Cuantitativos Aplicados, FAUBA, Capital Federal, Argentina G. Rubio Cátedra de Fertilidad y Uso de Fertilizantes, FAUBA, Capital Federal, Argentina