Nitrogen mineralisation and N2O emissions in pure and mixed-species plantations of Eucalyptus urograndis and Acacia mangium

We hypothesised that N inputs to the soil from residues of adult trees of Acacia mangium Willd. increase soil nitrate availability and consequently induce higher nitrous oxide (N2O) fluxes, irrespective of being in pure or mixed stands with Eucalyptus. A randomised block-design experiment was set up on Haplic Planosol in Brazil to study the impact of monospecific stands of Eucalyptus urograndis (Eucalyptus urophylla S. T. Blake × Eucalyptus grandis W. Hill ex Maiden) fertilised with 120 kg N ha−1 (E100+N) and A. mangium (A100), along with the mixture of both species (E50A50) on soil N mineralisation and its relationship with soil N2O emissions. In situ monitoring of N mineralisation, N2O emissions and the soil N stocks was carried out between five- and six-year-old plantations. The total soil net mineralisation of N that was accumulated in plantations A100 and E50A50 was on average 3.5- and 2.5-times greater than in the E100+N plantation. The NO3− produced throughout the year by the plantations was proportional to the total net mineralisation, according to the following order of production scale: A100 > E50A50 > E100+N. Furthermore, N2O emissions in the plantations that included A. mangium (A100 and E50A50) were significantly higher in some periods of the year, as compared with in the E100+N plantation. This pattern caused a more pronounced curve of accumulated N2O emissions under A. mangium plantations (pure and mixed) as compared with the monospecific Eucalyptus plantation (E100+N). However, the magnitude of N accumulation emissions suggests that mixed plantations could increase the nutritional status of sandy soils.