Effects of soil-surface mulching on organic carbon, inorganic carbon and light fraction organic carbon in dryland soil

To sustain the balance of soil carbon pool, decrease output of soil organic carbon and increase soil labile organic matters have been proved playing an important role in enhancing soil fertility. Long-term field experiments have been carried out with winter wheat and fallow rotation system since 2002, and soil samples were taken from 0-40 cm soil layers to study the effects of conventional tillage (CT), plastic-film mulching (PM) and wheat straw mulching (SM) on soil organic carbon (SOC), inorganic carbon and light fraction organic carbon (LFOC). The results showed that PM or SM increased significantly biomass and grain yield. Different soil surface mulching had no significant effects on soil inorganic carbon contents and its distribution in 0-40 cm soil layers. PM treatment significantly decreased SOC contents in 0-5 cm soil layer, but decreased LFOC by C 6.1~74.5 mg/kg compared to CT in 0-40 cm soil layers. In contrast, wheat straw mulching significantly increased LFOC in 0-5，5-10 and 10-20 cm soil layers by C 235.2，190.0 and 144.9 mg/kg, respectively. In the mean time, SM also tend to decrease the carbon content in light fraction organic matter (LFOM) in 0-10 cm soil layers and increase the proportions of LFOC to SOC in 0-20 cm soil layers compared to the CT as well as PM. This indicates that long-term soil surface mulching with plastic film was not profit for organic carbon accumulation in dryland soil. Mulching soil surface with crop straw not only enhances the soil light fraction organic carbon accumulation in surface soil, but also improves soil C and N composition.