Organic Matter Quality and Microbial Activity in Soils Managed With Brachiaria Succession

ABSTRACT Background Although succession systems and brachiaria improve soil quality, gaps remain in microbial community dynamics, activity, and soil organic matter stocks. Methods The objective was to evaluate the carbon (C) and nitrogen (N) stocks of soil organic matter fractions and their distribution, molecular characterization, enzyme activity associated with the C, sulfur (S), and phosphorus (P) cycles, and microbial composition in succession crops of corn, soybeans, and cotton without prior use of brachiaria in succession (NB) and with brachiaria planted 24 months ago (B24), 6 months ago and desiccated (B6D), and 2 months ago and still alive (B2L), at different depths. Results Stocks decreased by 15% and 14% for B24, 32% and 27% for B6D, and 7% and 3% for B2L, respectively, for C and N at a depth of 1 m, when compared to NB. The B6D system had the highest N stocks in the particulate fraction of organic matter at depth, as well as the highest arylsulfatase activity (37.6 mg p ‐nitrophenol kg −1 soil h −1 ). β‐Glucosidase activity was driven by the supply of particulate material and readily available C to microorganisms, as observed by C stocks in the dissolved fraction. There was no difference between treatments for acid phosphatase activity. The stabilization of soil organic matter is directly associated with the presence of recalcitrant compounds, such as lipids, lignin, and alkanes (14–26). Conclusions Microbial attributes varied across land‐use systems and soil depths, with higher bacterial biomass observed in some brachiaria ‐based systems at greater depths. However, these responses were not accompanied by increases in total C and N stocks or in soil organic matter fractions, and their implications for C sequestration require further evaluation in long‐term studies.