Characteristics And Mechanism Of Sediment Yield And Organic Carbon Loss In Sloping Cropland And Watershed Of Red Soil

Red soil hilly region in the south is a major land resource and it plays an important role in China's agricultural production.At the same time,the red soil hilly region is the second largest soil erosion area in China,and the hydraulic erosion is highly serious.Soil erosion can damage the production and living facilities,cause the deterioration of the ecological environment,meanwhile destroy the soil structure,resulting in soil fertility and quality degradation.As an important factor to characterize soil fertility,soil organic carbon were used to explore the situation of organic carbon loss caused by soil erosion in red soil region,analyze the influence factors and mechanism of soil organic carbon loss.It have a great significance to strengthen ecological security construction and maintain the sustainable development of social economy in the red soil region.Soil and water loss mainly occurs in sloping cropland in the red soil region.As the main regional unit in the red soil region,the agricultural watershed is interlaced with croplands and paddy fields and is the main agricultural activity area.The study,with the sloping cropland and agricultural watershed of red soil as an object of research,in order to investigate the impact of different fertilizations on soil erosion and to clarify the dynamic of organic carbon loss carried by soil sediment in a sloping cropland of red soil during 2015-2017 period.Five fertilization treatments were composed of no fertilizer?CK?,inorganic NPK fertilizer?NPK?,NPK fertilizer plus rice straw mulch?NPK+Str?,NPK fertilizer plus rice straw-derived biochar?NPK+BC?,and NPK fertilizer plus swine manure?NPK+OM?;in the watershed,the soil organic carbon and its spatial variability at different depths in 2012 were analyzed by grid sampling.Meanwhile,by monitoring the change of water turbidity in 2017,the characteristics of erosion and sediment yield and organic carbon loss carried by soil sediment were analyzed.The main conclusions of this article as follows:1.There are differences in runoff and sediment loss under five fertilization treatments.Results show that in terms of volume of runoff,the five treatments displayed an order ofNPK+BC>CK>NPK>NPK+OM>NPK+Str?P<0.05?,and in terms of sediment loss was in the order of CK?NPK+BC?NPK>NPK+OM>NPK+Str?P<0.05?.About 69⁸3%of the surface runoff and 70%⁸9%of the soil erosion occurred during the peanut growingseason?April-August?.2.Compared with Treatment NPK treatments,Treatment NPK+Str,NOK+BC andNPK+OM significantly increased the concentration of organic carbon in the sediment?P<0.05?.However,Treatment NPK+BC was the highest in total organic carbon loss via soil sediment(C 52.1 t·km^-2·a^-1),while Treatments NPK+OM and NPK+Str the lowest.Nosignificant seasonal changes were observed in organic carbon content in sediment.About 78%of the loss of organic carbon with sediment occurred during the peanut growing season?April-August?in each year.3.By establishing a semivariogram and performing Kriging spatial interpolation,there are differences in soil organic carbon content at different depths in the agricultural watershed,and organic carbon appears in the surface layer?0¹5 cm?.Soil organic carbon content has strong spatial autocorrelation.Soil organic carbon in surface layer?0¹5 cm?is greatly affected by random factors such as fertilization and tillage.Soil organic carbon is affected by soil structure in deeper layer?15³0 cm?.The spatial distribution of soil organic carbon content at different depths showed an increasing trend from north to south.4.The OBS-3A and HOBO pressure water level gauges were used to continuously monitor the dynamic changes of turbidity and runoff in the watershed.The dynamic change of water volume in the main outlet of the basin is closely related to precipitation.The annual amount of sediment loss in the basin is 738.77 t·km^-2.The organic carbon shows obvious enrichment in the sediment,and the organic carbon loss carried by soil sediment is 19.08 t·km^-2.The amount of organic carbon loss carried by soil sediment in April-September account for 88%of the total amount of organic carbon loss in the year.