The immediate effects of downslope cornstalk mulch (DCM) on sediment yield, runoff and runoff-associated dissolved carbon loss in a representative hillslope, Southwestern China

Abstract

Dissolved carbon plays a pivotal role in carbon cycles and potentially affects ecological processes of water body. While stalk mulch can regulate soil and water losses, its effects on the export of dissolved carbon from soils are poorly understood. The main objective of this study was to determine the effects of rainfall intensity and downslope cornstalk mulch (the lengths of cornstalks along the slope, DCM) on runoff, sediment yield and dissolved carbon losses, including dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and dissolved total carbon (DTC). A series of field rainfall simulations were conducted on the steep fallow land (20 °) locating in a representative hillslope of southwestern China that experiences severe soil erosion, and data for runoff, sediment and dissolved carbon loss rates were obtained from triplet parallel plots (1.5 m long and 1 m wide for each one) using 60 min rainfall simulations at 30 and 90 mm h−1 intensities on bare soils and 90 mm h−1 intensity on soils with DCM (air-dried whole plants, 60% coverage and weight 1.65 kg), respectively. Rainfall intensity showed positive effects on runoff generation, sediment yield and loss rates of DIC, DOC and DTC. The plots with immediate DCM had no difference in runoff generation, but were 71.1% lower in sediment yield and 53.9% higher in DOC loss rate relative to the bare plots. The contribution of DIC to DTC increased from 35.9% to 59.6% with the increasing rainfall intensity. Cornstalk mulching appeared efficient in reducing sediment yield, but its adoption is likely to dramatically enhance DOC exports from soils with concerns for the quality of inland waters. Further research studies are required to discriminate between soil and cornstalk mulch contribution to DOC exports by overland flow.