Combined effect of nitrogen fertiliser and leaf litter carbon drive nitrous oxide emissions in tropical soils

• Published in: Nutrient cycling in agroecosystems Vol. 118; no. 2; pp. 207 - 222
• Main Authors: Pandeya, Hemant Raj, Friedl, Johannes, De Rosa, Daniele, Asis, Constancio Tony, Tilbrook, Joanne, Scheer, Clemens, Bristow, Mila, Grace, Peter R., Rowlings, David W.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01-11-2020; Springer Nature B.V
• Subjects: Agricultural management; Agriculture; Biomedical and Life Sciences; Carbon; Dry matter; Emissions; Fertilizers; Groundwater; Intergovernmental Panel on Climate Change; Leaf litter; Leaves; Life Sciences; Nitrogen; Nitrous oxide; Orchards; Original Article; Soil investigations; Substrates; Tropical environments; Tropical soils; Urea; Leaf litter/residues; Tropical savannah; Fruit tree crops/orchard; Mango; Emission factor; Nitrous oxide (N; O
• ISSN: 1385-1314; 1573-0867
• DOI: 10.1007/s10705-020-10094-6

Intensification of agriculture in the tropics is likely to increase reactive nitrogen (N) losses in the form of nitrous oxide (N
2
O), however, drivers of emissions from tropical soils remain poorly understood. This study investigated the effect of leaf litter and urea fertiliser on N
2
O emissions from two Australian tropical mango orchards. Treatments included urea (25 g N m
−2
), leaf litter (1500 g m
−2
dry matter), their combined application, and untreated control. Up to 80.5 ± 8.4 mg N
2
O-N m
−2 
were lost within two weeks of treatment application, accounting for more than 60% of annual N
2
O emissions. Indirect emissions > 30 mg m
−2
d
−1
were recorded at one site, potentially resulting from groundwater transported N. Highest annual N
2
O emissions were observed from Litter + Urea with 130.4 mg N
2
O-N m
−2 
y
−1
, exceeding those from Urea-Only by a factor of two and those from Litter-Only by a factor of four. This resulted in residue and fertiliser emission factors (EF) of < 0.01–0.37%, well below the IPCC and Tier 2 defaults, with whole orchard losses equivalent to 0.19–0.66 kg N
2
O-N ha
−1
. The findings suggest N
2
O is N limited when no N fertiliser is applied, even when applying large amounts of litter-N, and by carbon (C) in the absence of litter. The combined effect of Litter + Urea on N
2
O emissions surpassed the effect of the sole application of litter and urea, demonstrating a critical interaction between both substrates. This interaction effect needs to be considered when developing management strategies aimed at increasing soil C in tropical soils.