The expansion of oil palm (Elaeis guineensis Jacq.) cultivation in degraded areas has increased in the Brazilian Amazon. Cultivation of oil palm in diversified agroforestry systems may be a relatively sustainable alternative to monocultures for crop expansion. Here, we evaluated the effect of oil palm cultivation systems on soil C, an important indicator of the soil quality of production systems. We assessed:(1) whether these systems of oil palm cultivation alter the potassium permanganate oxidizable C content (POx-C) and the carbon management index (CMI); and (2) how the POx-C varied among management zones (harvest path, leaf pile, weeded circle, and diversified strip). The soil C indices of the oil palm cultivation systems were also compared with those of secondary forests. POx-C varied consistently based on the pattern agroforestry > secondary forest = monoculture, ranging from 0.95 ± 0.14 (agroforestry) to 0.66 ± 0.10 gÁkg À1 (monoculture). The POx-C pattern among management zones was pile > diversified strip = weeded circle > harvest path. The CMI was higher in agroforestry than in monoculture. We found that these indices are sensitive to land-use systems and management practices that affect organic matter input. Organic fertilization and species diversity likely drive the improvement of soil quality in agroforestry systems than in monocultures through C input to the soil directly and indirectly, by creating favorable conditions for the action of root and fauna that in turn positively affect soil C. Therefore, we postulate that soil quality improves through oil palm agroforestry than through oil palm monocultures.

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