In order to reveal the response of the soil erosion and organic carbon loss on purple slope farmland with contour ridges to slope gradient

characteristics of the runoff

sediment yield and organic carbon loss on different slopes were studied during maize seedling stage through surveying field runoff plots and simulating rainfall artificially. The results showed that during maize seedling stage

the surface runoffs on different slopes were stable in the initial stage of rainfall

and they gradually increased with the duration of rainfall. On 10° slope

the interflow did not change at the beginning of rainfall

and gradually increased with rainfall duration

while on 15° and 20° slopes

the interflow showed a gradually increasing trend with rainfall duration. The erosion intensities of different slopes listed in the order of 20°＞15°＞10°

and erosion intensity of 20° slope was significantly higher than those of 10° and 15°slopes. The concentrations of total organic carbon (TOC) and dissolved organic carbon (DOC) in surface runoff decreased with the increasing of rainfall time on different slopes

and the organic carbon mass concentration followed the order of 20°＞15°＞10°

while the TOC and DOC concentrations in interflow firstly increased and then decreased

and organic carbon mass concentration followed the order of 10°＞15°＞20°. And the concentrations of TOC and DOC in surface runoff were not very different with those in interflow; TOC and DOC migration fluxes in interflow were both greater than those in surface runoff on different slopes

organic carbon migration flux in surface runoff followed the order of 20°＞15°＞10°

while organic carbon migration flux in interflow showed contrary order

and DOC migration flux accounted for 90% of TOC migration flux in runoff. The organic carbon content in sediment decreased with the increasing of slope gradient

and on the same slope

the organic carbon content in sediment decreased with the duration of rainfall. The organic carbon was enriched obviously in sediment

and the enrichment ratio decreased with the increasing of slope gradient. Therefore

the organic carbon in runoff was mainly lost in the form of DOC on purple sloping farmland

and interflow was the main mode of the DOC migration.