Conversion of degraded forests to oil palm plantations in the Peruvian Amazonia: Shifts in soil and ecosystem-level greenhouse gas fluxes

Oil palm (OP) expansion and associated forest clearance can significantly impact greenhouse gas (GHG) fluxes. We investigated carbon stocks and soil GHG (N 2 O, CO 2 , CH 4 ) fluxes in a degraded forest and an adjacent 17-year-old OP plantation in Peruvian Amazonia. The plantation comprised three nitrogen (N) fertilizer treatments: 0 (OPN0), 84 (OPN1), 168 (OPN2) kg N ha −1 y −1 . Carbon stocks were inventoried across all pools. GHG and environmental parameters were monitored monthly for 11 months and (bi)daily when fertilizing the OP, with measurements taken both near and far from trees/palms. Ecosystem-scale CO 2 equivalent losses from the conversion were computed by balancing carbon stock losses against N 2 O emission changes. N 2 O emissions (kg N ha −1 y −1 ) in the forest (6.7 ± 1.2) where litterfall N inputs were large (213 kg N ha −1 y −1 ) were 11, 5, and 3 times the emissions in OPN0 (0.6 ± 0.2), OPN1 (1.4 ± 0.2), and OPN2 (2.3 ± 0.3). In the plantation, 1 % of the N fertilizer applied was released as N 2 O. Across ecosystems, N inputs primarily controlled N 2 O emissions. Soil respiration (Mg C ha −1 y −1 ) was 1.4 times higher in the forest (9.1 ± 0.6) than in the plantation (7.3 ± 1, 5.5 ± 0.5, 6.5 ± 0.3 in OPN0, OPN1, OPN2). The forest was a soil CH 4 (kg C ha −1 y −1 ) sink (-1.5 ± 0.3) while all OP treatments were sources (0.2 ± 0.3, 0.7 ± 0.5, 0.2 ± 0.4 in OPN0, OPN1, OPN2). Ecosystem carbon stock losses from forest-to-OP conversion were substantial (196.8 ± 44.0 Mg CO 2 ha −1 15 y −1 ) and partially offset (14–20 %) by decreased N 2 O emissions. Complementary studies for this transition are needed to improve global GHG assessments. • Soil N 2 O emissions were higher in the degraded forest than the oil palm plantation. • Soil respiration was higher in the degraded forest than the oil palm plantation. • The soil was a CH 4 sink in the degraded forest, a CH 4 source in the oil palm plantation. • Degraded forest conversion to oil palm plantation substantially reduced ecosystem C stocks. • C stock losses from the conversion were 14–20 % offset by decreased N 2 O emissions.