Soil organic carbon fractions in agroforestry system in Brazil: seasonality and short-term dynamic assessment

Abstract

ABSTRACT Adopting land-uses that contribute with a considerable litter input can affect the accumulation, protection, and bioavailability of organic carbon in the edaphic environment, compromising the different compartments of soil organic matter (SOM) and the associated benefits. Moreover, changes in seasons can influence the dynamic of SOM. Notably, the mechanisms involved in SOM stabilization and storage, particularly in agroforestry production areas, are still poorly explored. This study aimed to verify if the contents of soil organic carbon (SOC) and the physical fractions of the SOM are modified as a function of agroforestry systems implemented in the short term, and verify if seasonality can affect the compartmentalization of SOM in agrifood systems. Also, we tested if the carbon management index (CMI) is sensitive to detecting management practices quality across the unmanaged pasture, different agroforestry systems, and a reference area (forest). We measured soil physical properties, SOC content in bulk soil, particular organic carbon (POC), and mineral-associated organic carbon (MAOC) fractions at three different depths (0.00-0.05, 0.05-0.10, and 0.10-0.20 m) in response to the adoption of agroforestry systems. Our results show that after a short period of implementation of agroforestry systems, significant changes were observed in SOC contents and the physical fractions of SOM in the most superficial layers (0.00-0.05 and 0.05-0.10 m), with emphasis on the particulate fraction of SOM. We verified that the seasonality affected the SOC, POC, and MAOC contents. We also found that the CMI index was more sensitive and efficient in detecting changes arising from seasonality and the management practices involved. According to this index, it was possible to verify that the agroforestry system with the highest density of species for biomass production (AS3) has been accumulating more carbon in the soil. Therefore, this study provides relevant information regarding soil carbon management in agroforestry systems.

Keywords

• soil carbon sequestration
• regenerative agriculture
• sustainability