Subtropical maize production and soil microbial communities show minimal response to earthworm bio-tillage

Conservation tillage has become an increasingly important practice for addressing soil degradation in agricultural systems, but its effectiveness on crop production remains uncertain, especially under humid conditions. Besides, earthworm bioturbation, a natural form of bio-tillage, can impact soil quality and crop production, but previous studies have failed to isolate and quantify the specific contribution of earthworm bioturbation in conservation tillage systems. The aim of this study was to investigate the effects of conservation tillage on subtropical farmland, with the goal of evaluating its suitability and recommending appropriate practices for humid conditions. A two-year field experiment was conducted on subtropical Ultisols and tested three tillage types (no-tillage, earthworm bio-tillage, and traditional rotary tillage) along with three organic matter inputs (none, straw return, and composted cow manure addition). Maize (Zea mays L.) yield and soil samples (0-10 cm) were collected after four growing seasons to determine the maize production, soil properties and microbial communities. Results showed that tillage type and organic matter input generally did not impact yield or aboveground biomass, except for a 14.4% and 33.5% reduction, respectively, under earthworm bio-tillage compared to traditional tillage under the straw input condition (p < 0.05). Tillage mainly affected soil phosphorus dynamic, while organic matter influenced pH and nitrogen dynamics. Both no-tillage and earthworm bio-tillage increased soil pH, organic carbon, nitrogen and phosphorus contents, especially with cow manure additions, and increased the general bacteria and gram-positive bacteria under none input. No-tillage significantly increased microbial biomass carbon, especially with none and straw inputs (over 6.3 times, p < 0.05). This study addresses a critical gap by evaluating the effects of no-tillage and earthworm bio-tillage with organic matter inputs. Here we show that conservation tillage practices, such as no-tillage and earthworm bio-tillage combined with appropriate organic matter inputs, are effective strategies for enhancing soil quality without adversely affecting crop production in subtropical sustainable agriculture.