Denitrification losses from an intensively managed sub-tropical pasture - Impact of soil moisture on the partitioning of N-2 and N2O emissions

作者：Friedl Johannes; Scheer Clemens^*; Rowlings David W; McIntosh Heather V; Strazzabosco Alice; Warner Daniel I; Grace Peter R

来源：Soil Biology and Biochemistry, 2016, 92: 58-66.

DOI：10.1016/j.soilbio.2015.09.016

• N-2-emissions
• N2O emissions
• N-2/(N-2 + N2O) ratio
• N-15 gas flux method
• Denitrification
• Pastures

Intensively managed pastures in subtropical Australia under dairy production are nitrogen (N) loaded agro-ecosystems, with an increased pool of N available for denitrification. The magnitude of denitriflcation losses and N-2:N2O partitioning in these agro-ecosystems is largely unknown, representing a major uncertainty when estimating total N loss and replacement. This study investigated the influence of different soil moisture contents on N-2 and N2O emissions from a subtropical dairy pasture in Queensland, Australia. Intact soil cores were incubated over 15 days at 80% and 100% water-filled pore space (WFPS), after the application of N-15 labelled nitrate, equivalent to 50 kg N ha(-1). This setup enabled the direct quantification of N-2 and N2O emissions following fertilisation using the N-15 gas flux method. The main product of denitrification in both treatments was N-2. N-2 emissions exceeded N2O emissions by a factor of 8 +/- 1 at 80% WFPS and a factor of 17 +/- 2 at 100% WFPS. The total amount of N-N-2 lost over the incubation period was 21.27 kg +/- 2.10 N-2-N ha(-1) at 80% WFPS and 25.26 kg +/- 2.79 kg ha(-1) at 100% WFPS respectively. N-2 emissions remained high at 100% WFPS, while related N2O emissions decreased. At 80% WFPS, N-2 emissions increased constantly over time while N2O fluxes declined. Consequently, N-2/(N-2 + N2O) product ratios increased over the incubation period in both treatments. N-2/(N-2+ N2O) product ratios responded significantly to soil moisture, confirming WFPS as a key driver of denitriflcation. The substantial amount of fertiliser lost as N-2 reveals the agronomic significance of denitrification as a major pathway of N loss for sub-tropical pastures at high WFPS and may explain the low fertiliser N use efficiency observed for these agro-ecosystems.

• 出版日期2016-1