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

Abstract

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.