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.