Nitrous oxide and methane fluxes in six different land use systems in the Peruvian Amazon

Abstract

[1] The contribution of different land-use systems in the humid tropics to increasing atmospheric trace gases has focused on forests, pastures, and crops with few measurements from managed, tree-based systems that dominate much of the landscape. This study from the Peruvian Amazon includes monthly nitrous oxide and methane fluxes from two cropping systems, three tree-based systems, and a 23-year secondary forest control. Average N 2 O fluxes from the cropping systems were two to three times higher than the secondary forest control (9.1 mg N m À2 h À1 ), while those of the tree-based systems were similar to the secondary forest. Increased fluxes in the cropping systems were attributed to N fertilization, while fluxes from the tree-based systems were related to litterfall N. Average CH 4 consumption was reduced by up to half that of the secondary forest (À30.0 mg C m À2 h À1 ) in the tree-based and low-input cropping systems. There was net CH 4 production in the high-input cropping system. This switch to net production was a result of increased bulk density and increased soil respiration resulting in anaerobic conditions. Reduced rates of N 2 O emissions, similar CH 4 consumption, and high C sequestration rates in these tree-based systems compared with mature forests, coupled with the large area of these systems in the humid tropics, may partially offset the past effects of deforestation on increased atmospheric trace gas concentrations. In contrast, cropping systems with higher N 2 O emissions, substantially reduced CH 4 consumption or even net CH 4 emissions, and little C sequestration exacerbate those effects.

Potential N2O emissions from leguminous tree plantation soils in the humid tropics

“…[20] Annual N 2 O emissions from secondary forest soils (0.33 kg N ha À1 ) are low relative to other tropical forests; e.g., tropical forest emissions are estimated at 0.01 -7.68 kg N ha À1 [Breuer et al, 2000] and Amazon secondary forests at 0.94 kg N ha À1 [Verchot et al, 1999] or 0.80 kg N ha À1 [Palm et al, 2002]. These low secondary forest emissions are comparable to those observed at primary forests in central Sumatra (0.13 kg N ha À1 and 0.39 kg N ha À1 [Ishizuka et al, 2002]), but relatively low compared to emissions from southern Sumatra forests (1.47 and 1.80 kg N ha À1 at sites showing high WFPS (90 -100% [Verchot et al, 2006]) and montane forests in central Sulawesi (0.29, 1.01, and 1.11 kg N ha À1 [Purbopuspito et al, 2006]).…”

Nitrous Oxide Emissions from Soils with Different Vertical Soil Moisture Distribution Patterns

“…Heavy-textured soils frequently produce higher N 2 O fluxes than light soils [38]. The N 2 O fluxes from fine-textured soils were significantly higher than those from coarse-textured soils [39][40][41][42]. In this research, N 2 O fluxes in all treatments from silty clay were significantly higher than those from sandy loam.…”

Tropical forests and adaptation to climate change: in search of synergies

“…For example, multi-story coffee with a leguminous tree shade canopy in Sumatra had N 2 O emissions five times higher than open-grown coffee and about half the CH 4 uptake (Verchot et al, unpublished data). In Peru, agroforestry systems (multi-strata coffee and a peach palm plantation) with leguminous cover crops had lower N 2 O emissions than both intensive and low-input agriculture, and similar emissions to a nearby secondary forest (Palm et al, 2002). Soil uptake of CH 4 was similar to other landuse systems, with the exception of the intensive agriculture site, which became a net source to the atmosphere.…”