The impact of periodic waterlogging on biochemical characteristics and mineralization of soil organic carbon in straw-return farmland

Periodic waterlogging is more common due to more frequent extreme precipitation but its impact on soil organic carbon (SOC) loss is obscure in straw-return farmland. We compared soil properties and biochemical characteristics of SOC (compositions of non-cellulosic and amino polysaccharides) in adjacent periodic waterlogged farmland (PWF) and non-waterlogged farmland (NWF) in a semi-humid warm temperate region. SOC mineralization was also measured at 60% (aerobic) or 100% (anaerobic) of field capacity at 25 °C for 82 days. The negative effect of periodic waterlogging on SOC contents and soil aggregate stability were observed in the 20–80 cm depth but were offset in topsoil (0–20 cm) due to straw-return. Periodic waterlogging increased the non-cellulosic sugar content and amino sugar content in SOC and the mass ratio of (galactose plus mannose) to (arabinose plus xylose) at 40–80 cm depth except at 0–40 cm depth. By the end of 82 days’ incubation, when aeration status changed from anaerobic to aerobic conditions, total C loss as CO₂ increased similarly (123.9%) in PWF and NWF soils in the top 40 cm, but more C loss occurred under PWF than under NWF (78.9% vs. 46.9%) in the 40–80 cm depth, which was probably ascribed to its higher non-cellulosic sugar and amino sugar content. Our result emphasized the importance of straw-return for maintaining soil quality under periodic waterlogged farmland.