Driving crop yield, soil organic C pools, and soil biodiversity with selected winter cover crops under no-till

No-till (NT) and cover crops (CCs) have been repeatedly recommended for building-up resilience of agro-ecosystems, enhancing soil biodiversity, and steering efficient nutrients cycling and yield. Yet, the overall impact of CCs on soil properties and dynamics during transition may highly change depending on CC species and interactions with field condition. In the present 3-yr field study, we (i) examined how selected CCs (i.e. rye [Secale cereale L.]; phacelia [Phacelia tanacetifolia Benth.] + white mustard [Sinapis alba L.]; Italian ryegrass [Lolium multiflorum Lam.] + crimson clover [Trifolium incarnatum L.] + Persian clover [Trifolium resupinatum L.]; hairy vetch [Vida villosa Roth] + crimson clover) affect yield performance in a crop sequence of maize (Zea mays L.), soybean (Glycine max L. Merr.), and maize under NT, and (ii) assessed the effects of CCs on inputs to the soil (i.e. biomass, carbon [C], and nitrogen [N]), soil organic C (SOC) and pools, as well as microarthropods and earthworms abundance and diversity. Grain yield during the initial 2-yr period was on average reduced with CCs by 1-23% in maize, and 1-33% in soybean. This effect was less evident with CC residues having low C:N ratio (< 20; i.e. hairy vetch + crimson clover) and erect habitus after termination (i.e. rye). Thereafter, CCs had no effect on maize yield the third year. Soil organic C and pools indicated that (i) the effect of our CC treatments over a 3-yr application is limited to the topmost 5 cm of soil, and (ii) the biomass input with CC residue and its C:N ratio are crucial for boosting soil C cycling. This was also the case for earthworm-related indicators, while arthropods mainly responded to different CCs in terms of evenness. Yet, our results on soil fauna showed that different groups or species need different time for showing effects, thus suggesting that responses may be fully effective in a >3-yr term. We concluded that CC mixtures that allow the best compromise between the high amount of residue and the low residue C:N ratio should be preferred for: (i) reducing possible detrimental effects on grain yield of maize and soybean, and (ii) enhancing soil C cycling and biodiversity. Therefore, selecting appropriate CC species in mixtures represents the main challenge at the field level for pursuing both objectives in the shortest timeframe. Within all options in summer crop sequences, here we reported that mixtures including leguminous cover crops might be primarily considered.