Soil type and cropping system as drivers of soil quality indicators response to no-till: A 7-year field study

Conventional agricultural practices (CAP) highly impacted soil functions involved in the provision of multiple ecosystem services. No-till (NT) has been repeatedly indicated as a key way to enhance soil fertility and biodiversity, while having a positive effect on the environment and climate change. However, experimental evidence to date shows contrasting effects of NT on physical parameters of soil fertility, as well as on soil organic carbon (SOC) storage and soil biodiversity especially if different soil types and cropping systems are considered. The objectives of the present 7-year field study were: (i) to unravel the effect of NT on SOC, soil bulk density, and water stability index (WSI) of soil aggregates across five different soil types (Silty Clay, Silty Clay Loam, Clay Loam, Silt Loam, and Sandy Loam) and cropping systems (silage vs grain production), (ii) to examine how soil fauna (i.e. microarthropods and earthworms) is affected by NT practices under those soil-crop conditions, and (iii) to assess relationships among responses of soil physical indicators (i.e. soil bulk density and WSI), SOC, and soil fauna. Our results showed that soil bulk density was generally not affected by 7-year NT across all soil types. At the same time, NT increased WSI. It follows that NT may increase stable rather than artificial tillage-derived porosity due to reduced soil disturbance, and increased SOC and biological activity. However, reduced importance for boosting aggregates stability should be attributed to NT where initial SOC is high, clay and silt are predominant soil fractions, and the rate of crop residue is low. Our findings suggest that NT may enhance SOC stock (on average 0.66 Mg C ha−1 year−1) in the 0–30 cm soil layer. However, we found (i) a tendency of NT to decrease SOC concentration in the 15–30 cm soil layer (on average −1.18 g C kg−1), and (ii) no SOC increase induced by NT if crop residues were not left onto the soil surface. Nevertheless, NT practices promoted (i) the microarthropods adaptation measured with the QBS-ar index (105.5 vs 64.7), and (ii) the increase of earthworm abundance (412 vs 123 individuals m−2), which are fundamental for enhancing nutrient cycling and soil porosity. Correlations among soil fauna (i.e. QBS-ar and earthworm density), soil physical parameters (i.e. soil bulk density and WSI), and SOC (i.e. concentration and stock) corroborates the hypothesis that soil fauna adaptation and proliferation are main detectors of soil quality and sensitive indicators of changes in soil tillage.