A climate change scenario and soil ammonium 'fixation' during the seasonal rice (Oryza sativa) growth in Portugal under intermittent flooding

Resumen

The newly fixed NH₄⁺ in clay minerals should be considered for an efficient management of plant nutrition. In a clay-loam soil cultivated in 2012 with rice under intermittent flooding and conventional agronomic practices, the dynamics of pH, N-inorganic and non-exchangeable NH₄⁺ was evaluated i) under field conditions, air temperature and atmospheric [CO₂] (375 µmol mol^-1 air) in Salvaterra de Magos (Portugal), and ii) under elevated temperature and temperature+[CO₂] in controlled microclimate. For that, open-top chambers were used to simulate the conditions of an increased mean air temperature (2-3 °C), alone or combined with increased [CO₂] (550 µmol mol^-1 air). Non-exchangeable NH₄⁺ was significantly higher under open-field conditions compared with the temperature elevation, with or without elevated atmospheric [CO₂]. Temperature elevation reduced the fixation rate of the cation, while the CO₂ concentration rise did not affect particularly the non-exchangeable form. Further studies are required for consolidation of these findings together with microbial communities and dynamics of C and N in soil.