Impact of agricultural practices, elevated temperature and atmospheric carbon dioxide concentration on nitrogen and pH dynamics in soil and floodwater during the seasonal rice growth in Portugal

•In paddy rice, soluble N and pH in floodwater were not affected by climate change.•Temperature + [CO2] elevation had no effect on available soil N but increased the pH.•Immediately after the basal dressing with NH4 fertilizer, NH4 was “fixed” in clay at a rate of 25%.•Climate change (elevation of temperature + [CO2] and of temperature alone) reduced NH4+ “fixation” by 10–11%.

Data on the movements of available N and non-exchangeable NH4+ in the soil are of crucial importance in designing an efficient plant N nutrition management scheme in paddy rice fields. To investigate the processes affecting the dynamics of N and pH under Mediterranean conditions, rice (Oryza sativa L. cv. Ariete) was cultivated in 2011 and 2012 in Salvaterra de Magos (central Portugal) under the following climate scenarios: (i) ambient temperature and ambient [CO2] in the open-field, (ii) elevated temperature (+3 °C) and ambient [CO2] in open-top chambers, and (iii) elevated temperature (+3 °C) and elevated [CO2] (+175 μmol mol−1) in open-top chambers. Plants were grown under an intermittent flooding regime. Soil and water samples were taken at eight different stages of plant growth, including before and after N basal and topdressing. Our study indicated that the processes underlying N changes in response to the timing of N fertilization were different depending on the N form. After basal dressing under aerobic conditions, both available and non-exchangeable NH4+ contents were increased. Following the topdressing under flooded conditions, the available content of soil N increased, whereas the non-exchangeable NH4+ content decreased. A negative relationship was found between soil pH and NH4+ “fixation” when roots were active, and vice-versa. Elevated temperature alone or in combination with elevated [CO2] had no effect on the total available N content in the soil and floodwater. Under elevated temperature, however, the non-exchangeable NH4+ content was significantly reduced (11%), with the same magnitude of change (10%) observed under co-elevation of temperature and [CO2]. These results suggested that non-exchangeable NH4+ in paddy fields might be insensitive to [CO2] elevation under Mediterranean conditions, while reductions observed under co-elevation of [CO2] and temperature might be associated with temperature alone. This information could be used to alter rice management practices and to adjust N application under climate change.