The objective of this work was to evaluate the impacts of fallow to crop cycle on the light fractions of soil organic matter (SOM) in a slash‑and‑mulch agroforestry system with different fallow vegetation management, in the Eastern Amazon. Sampling was carried out in the pre‑fallow, post‑fallow, and post‑cultivation stages. Stocks of free light organic matter (F‑LOM) and occluded light organic matter (O‑LOM), total organic carbon (TOC), total nitrogen (TN), and C and N stocks on F‑LOM and O‑LOM were determined. There was no effect of fallow management in the studied variables, except for TN at 30-50 cm and O‑LOM at 10-20 cm soil depth. Light organic matter fractions were affected by the phases of the agroforestry slash‑and‑mulch system. The highest C and N stocks were observed in F‑LOM in the post‑fallow and post‑cultivation periods. Although there was no increase in total C and N stocks, the increase in F‑LOM and its stocks of C and N indicates the improvement and maintenance of soil quality in the slash-and-mulch system of biomass accumulated in 23 months of fallow, even after crop phase.
Amazon; organic matter cycling; fallow enrichment; organic matter fractionation; labile organic matter; soil quality
