Effect of Different Irrigation Methods on Dissolved Organic Carbon and Microbial Biomass Carbon in the Greenhouse Soil

The objective of this study was to investigate the contents and distribution of dissolved organic carbon (DOC) and microbial biomass carbon (MBC) at 0-100 cm soil depth under three irrigation treatments, viz., subsurface, drip and furrow irrigation in the greenhouse soil. The soil samples were collected at different depths (0-100 cm), and the contents of soil total organic carbon (TOC), DOC and MBC were analysed. The experiment was conducted for 10 yr, during which period the application of fertilizers and crop management practices were kept identical. The results showed that the contents of TOC, DOC and MBC were significantly affected by different irrigation regimes, decreased with the increase of soil depth. TOC at 0-10 and 80-100 cm soil depths followed the order of furrow irrigation > subsurface irrigation > drip irrigation, whereas at the depth of 10-80 cm followed the order of subsurface irrigation> furrow irrigation > drip irrigation. DOC and MBC contents at 0-100 cm soil depths followed the order of furrow irrigation > drip irrigation > subsurface irrigation, and drip irrigation> furrow irrigation> subsurface irrigation, respectively. The ratios of DOC and MBC to TOC accounted for 4.98-12.87% and 1.48-2.82%, respectively, which were the highest in the drip irrigation treatment, followed were in the furrow irrigation treatment, and the lowest in subsurface irrigation treatment. There were significant positive correlations among the contents of DOC, MBC and TOC in all irrigation treatments. The furrow irrigation facilitated the accumulation of TOC and DOC, while drip irrigation increased the M BC. The content of TOC and the ratios of DOC to TOC were the lowest in subsurface irrigation treatment.