Which soil microbial indicators should be included in routine laboratory tests to support the transition to sustainable management of arable farming systems? A meta-analysis

• Clay, OM, pH, trial duration and sampling depth modulate indicator responses. • Integrating microbiological indicators to routine soil analysis improves diagnostics. • Microbial indicators are relevant for assessing crop diversification effect on soil. • Microbial indicators inform on nutrient cycling, OM transformation and soil structure. • SOC and STN inform on soil organic status under C input and reduced tillage practices. Our research aims to address the gap in understanding the sensitivity of multipurpose active pools of soil organic matter (SOM) and microbiological indicators, in addition to the usual physico-chemical measurements, to assess the effects of the shift from conventional to sustainable management practices under various pedoclimatic conditions. We conducted a meta -analysis (166 articles) on the sensitivity of these indicators on six practices: exogenous organic matter input (EOM), crop residue retention (RR), cover crop introduction (CC), crop rotation /diversification (CR), tillage reduction (TR), and conversion from conventional to innovative or organic systems (IOS). Random effects models considering the natural log of the response ratio were applied. Our study showed that climatic factors did not significantly influence indicator responses, while clay content, organic matter, pH, trial durations, and sampling depth significantly modulate the response of soil indicators. In detail, our results emphasized that both physico-chemical (soil organic carbon (SOC) and total nitrogen (STN) contents) and microbiological indicators (e.g., microbial biomass carbon (MBC), total phospholipids fatty acids (PLFA), and B-glucosidase (B-GLU)) were sensitive to EOM, RR, CC, and TR. For instance, CC significantly increased SOC (+7%) and STN (+8%), as well as MBC (+14 %), total PLFA (+19 %), and B-GLU (+11 %). On the other hand, CR and IOS practices did not impact SOC and STN, contrary to some microbiological indicators. For these two practices, MBC increased between 7 and 34 % and PLFA between 8 and 24 %. Moreover, B-GLU raised by + 58 % with IOS practice. This suggests that the microbiological indicators may be more responsive to specific agricultural practices, such as CR and IOS, even if the changes they induce are not immediately related to carbon inputs. SOC and STN provide information on the changes in the organic status of soil under carbon input practices and TR, though they are less sensitive to crop diversification and innovative farming in short-term studies, highlighting the time needed for sustainable management practices to modify soil health. Microbiological indicators (MBC and PLFA) and enzyme activities (FDA, B-GLU, and URE) showed greater sensitivity to a large range of agricultural practices, regardless of the age of agricultural practice, suggesting their potential use as more responsive, early, and versatile indicators in evaluating soil health.