Long-term tillage systems impacts on soil C dynamics, soil resilience and agronomic productivity of a Brazilian Oxisol

• No soil disturbance and high biomass-C input contribute to C sequestration in long-term no-till.
• Continuous C flow from crop residues increases labile C and addresses C migration to mineral associate-C.
• Preserving surface-soil C fractions and labile C increases SOC stock, and restores soil resilience.
• SOC stock and labile C increases enhance the relationship with agronomic productivity in long-term no-till.

No-till (NT) cropping systems have been widely promoted in many regions as an important tool to enhance soil quality and improve agronomic productivity. However, knowledge of their long-term effects on soil organic carbon (SOC) stocks and functional SOC fractions linking soil resilience capacity and crop yield is still limited. The aims of this study were to: (i) assess the long-term (16 years) effects of tillage systems (i.e., conventional – CT, minimum – MT, no-till with chisel – NTch, and continuous no-till cropping systems – CNT) on SOC in bulk soil and functional C fractions isolated by chemical (hot water extractable organic C – HWEOC, permanganate oxidizable C – POXC) and physical methods (light organic C – LOC, particulate organic C – POC, mineral-associated organic C – MAOC) of a subtropical Oxisol to 40 cm depth; (ii) evaluate the soil resilience restoration effectiveness of tillage systems, and (iii) assess the relationship between the SOC stock enhancement and crop yield. The crop rotation comprised a 3-year cropping sequence involving two crops per year with soybean (Glycine max, L. Merril) and maize (Zea mays L.) in the summer alternating with winter crops. In 2005, the soil under CNT contained 25.8, 20.9, and 5.3 Mg ha−1 more SOC (P < 0.006) than those under CT, MT, and NTch in 0–40 cm layer, representing recovery rates of 1.61, 1.31, and 0.33 Mg C ha−1 yr−1, respectively. The relative C conversion ratio of 0.398 at CNT was more efficient in converting biomass-C input into sequestered soil C than NTch (0.349), MT (0.136), and CT (0.069). The soil under CNT in 0–10 cm depth contained ∼1.9 times more HWEOC and POXC than those under CT (P < 0.05), and concentrations of LOC and POC physical fractions of SOC were significantly higher throughout the year under CNT. Considering CT as the disturbance baseline, the resilience index (RI) increased in the order of MT (0.10) < NTch (0.43) < CNT (0.54). Grain yield was positively affected by increase in SOC stock, and an increase of 1 Mg C ha−1 in 0–20 cm depth resulted in an increase in yield equal to ∼11 and 26 kg grain ha−1 of soybean (R2 = 0.97, P = 0.03) and wheat (R2 = 0.96, P = 0.03), respectively. The data presented emphasizes the role of labile fractions in the overall SOC accumulation processes in soils managed under CNT and their positive impacts on the soil resilience restoration and on agronomic productivity.