objective was to examine if these treatments could affect soil and floodwater chemical characteristics (NH4+, NO3–and pH), with a particular emphasis on the mechanism of “fixation”/diffusion of soil NH4+. In a Portuguese clay soil cultivated with rice (Oryza sativa L. cv. Ariete) in 2011 and 2012, under the intermittent flooding regime and conventional agronomic practices, the dynamics of available N, non-exchangeable NH4+ and pH should be evaluated in the soil and floodwater, under (i) the ambient temperature and ambient [CO2] in open-field, and under (ii) the elevated temperature (+3 °C) and ambient [CO2]- and (iii) elevated temperature (+3 °C) and elevated [CO2] (+175 μmol mol−1 air) in controlled open-top chambers (OTCs) placed in the field.