Oil palm agroforestry systems store more carbon and nitrogen in soil aggregates than monoculture in the Amazon

Agroforestry systems (AFSs) are known to store more carbon and nitrogen in the soil when compared with monocultures. However, studies involving carbon and nitrogen in soil aggregates in oil palm plantations, an important global commodity, in AFSs and monocultures are still scarce. Therefore, the objective of this study was to examine whether oil palm AFSs are able to store more carbon and nitrogen in soil aggregates than when planted in monoculture. We collected soil samples in the 0–10, 10–20, and 20–30 cm layers in an oil palm AFS (10 years old) and in an oil palm monoculture (9 years old) in Tomé-Açu, Eastern Amazon, Brazil. We determined soil aggregate stability, carbon and nitrogen contents in macro and microaggregates, and root biomass. Overall, more carbon was stored in the macroaggregates than in the microaggregates in the oil palm plantations. The carbon storage was higher in macro and microaggregates in the AFSs (macro: 12.97 ± 0.35 and micro: 0.53 ± 0.01) than in the monoculture (macro: 11.60 ± 0.19 e micro: 0.29 ± 0.01) in the 0–10 cm layer of the soil. The total soil carbon stock in the 0–30 cm layer was higher in the AFSs (38.08 ± 0.13 Mg ha⁻¹) than in the monoculture (31.79 ± 1.23 Mg ha⁻¹). The AFSs showed a trend towards greater aggregate stability (range throughout the soil profile 4.70 ± 0.07 to 3.31 ± 0.16 mm) compared to the monoculture (4.71 ± 0.02 to 2.71 ± 0.23 mm). Therefore, oil palm AFSs have a greater potential to store carbon in soil aggregates and, consequently, contribute more to climate change mitigation than oil palm monocultures. As such, our results have important implications for the sustainable cultivation and exploitation of the oil palm in the Amazon and in other regions of the world.