Responses of soil organic carbon, microbial biomass carbon, and microbial quotient to ground cover management practices in Chinese orchards: a data synthesis

Soil microbial quotient (SMQ), the ratio of soil microbial biomass carbon (SMBC) to organic carbon (SOC), is considered a key predictor of soil quality. However, the variations in SMBC and SMQ under ground cover management (GCM) in orchard systems remain poorly understood.

This study established a national database of SOC, SMBC, and SMQ, as well as associated climatic and edaphic factors, and agronomic practices from 288 field experiments across China. We leveraged the data to assess the responses and controlling factors of SOC, SMBC, and SMQ to GCM practices using a meta-analysis.

Our findings demonstrate that GCM significantly increases SOC (20%), SMBC (35%), and SMQ (19%) compared to conventional clean (bare ground) tillage. The categorical meta-analyses reveal that the response varies with management and environmental factors. The effect of GCM on SOC, SMBC, and SMQ is prominent in tropical rainy areas with low SOC content (< 10 g kg⁻¹), neutral soils (pH = 6–8), full cover with live grass, and shallow soils. Furthermore, the random forest modeling further demonstrates that soil depth is the dominant driver for responses of SOC, SMBC, and SMQ to GCM. The GCM-induced changes in SOC, SMBC and SMQ decline significantly as soil depth increased. The significant increase in SMQ was mainly observed in the upper 40 cm soil layer, which indicates that the ability of microorganisms to assimilate carbon decreases with soil depth.

Overall, we conclude that GCM practices could improve carbon sink and boost biological soil health in Chinese orchards. The response, however, varied depending on local environmental factors. We also highlight that a careful assessment of the site-specific conditions is needed to determine the appropriate GCM practices for potential benefits.

1. microbes assimilate SOC; 2. SOC decomposition releases CO₂; 3. microbial growth produces CO₂; and 4. the microbial necromass and byproducts are returned to soil. Numbers in parentheses represent the sample size. SOC, soil organic carbon; SMBC: soil microbial biomass carbon; SMQ: the ratio of SMBC to SOC; MAT, mean annual temperature; MAP, mean annual precipitation; TN, total nitrogen.