Management Practices Affect Soil Carbon and Physical Quality in Oil Palm Agroforestry Systems in the Amazon

Agroforestry systems (AFSs) with oil palm are expected to have better soil quality than monocultures of this crop. The variation in soil physical quality between oil palm management zones is related to carbon input and is well known in monocultures, but poorly studied in oil palm AFSs. Here we determined whether management practices change the carbon content and physical quality of soil in oil palm AFSs. We collected undisturbed and disturbed soil samples at different management zones (weeded circle, harvest path, leaf pile, and diversified strip) from the 0-5-, 5-10-, 10-20-, and 20-30-cm soil layers in oil palm AFSs in Eastern Amazon, Brazil. We determined the soil water retention curve, density, aggregation, penetration resistance, and carbon content. We performed principal component analysis to evaluate the influence of management on carbon content and physical properties in different soil layers. Overall, the management zones where there was no machinery traffic (weeded circle, leaf pile, and diversified strip) exhibited a higher carbon content and better physical quality in the surface soil layers (0-5 and 5-10 cm). These zones differed from the harvest path, which showed worse soil physical quality, i.e., lower soil aggregation, porosity, water retention, and carbon content, and greater soil density, compaction, and penetration resistance. Management practices that increase carbon levels on the harvest path should be prioritized to reduce the degradation of soil physical quality. Therefore, our results can help guide a more sustainable management of the soil in oil palm cultivation areas in the Amazon.