Effects of earthworms and straw additions on soil nitrogen under different tillage practices

No tillage greatly increases earthworm abundance due to low disturbance and residue returning, while earthworms strongly influence soil structure and soil organic matter dynamics as well.How will earthworms combined with residue returning affect distribution and decomposition of soil N? Aiming at understanding the effects of earthworms and straw adding on total N and active nitrogen fractions, by using undisturbed soils, we conducted a 30-day incubation experiment with earthworms and maize residue additions under no tillage(NT) and conventional tillage(CT) systems.The results showed that the contents of soil total nitrogen and soil active nitrogen in NT were higher than those in CT or equal to CT.The effects of earthworm and straw on soil nitrogen dynamics were different under CT and NT.The addition of straw decreased soil active nitrogen content in CT and the total nitrogen and active nitrogen contents in NT, respectively.In contrast, the earthworm decreased soil active nitrogen content in CT, while increased the total nitrogen and active nitrogen content in NT.The effect of earthworm and straw coexisting in conventional tillage would be less than the effect of a single role but still played a role in reducing nitrogen content; parts of the effect from earthworm and straw coexisting in NT was offset compared with the influence of single factor(earthworm or residue returning), which resulted in the N content ranging between the values under single earthworm and single straw treatments.This result would help us to select the appropriate farming measures and find out the optimal amount of straws returned to the field for maintaining soil fertility and reducing soil fertilizer.