| Soil detachment is the initial stage of soil erosion process, and also is theprincipal sediment source of subsequent transport and deposition. It is usually affectedby a specific hydraulic condition, soil properties, and the growth of root system.During the vegetation growing season, the growth of root system will cause thetemporal variation of soil properties. However, many of those soil properties fluctuategreatly over time, which can certainly lead to the temporal variation in soildetachment; previous limited studies have shown that the temporal variation in soildetachment capacity by overland flow was only influenced by some of soil propertiesin the loess belt of Europe. Nevertheless, previous researches were mainly focused onthe gentle slope, the temporal variation in soil detachment capacity by overland flowand its influencing factors under steep slope are not fully understood yet. In the LoessPlateau of China, soil erosion in the cultivated lands，which is considered as theprincipal sediment source delivered into the Yellow River, has long been a centralconcern. In the Loess Plateau, the growth of crop root system may cause the temporalvariation of soil properties. However, many of those soil properties fluctuate greatlyover time, which can certainly lead to the temporal variation in soil detachmentprocesses. At present, it is still unclear for the temporal variation in soil detachmentcapacity by overland flow and the potential influencing factors during one growingseason.This study was carried out to determine the effects of soil properties and croproots on soil detachment process in maize (Zea mays L.), millet (Setaria italica),soybean (Glycine max), and potato (Solanum tuberosum L.), investigate temporalvariation in soil detachment and its influencing factors, and establish soil detachment model based on a specific hydraulic condition, soil properties, and the growth of rootsystem. Soil detachment capacity was measured in a hydraulic flume with adjustablebed gradients. This study can provide useful information for revealing soil detachmentmechanism, evaluating the soil and water conservation function of crop root system,and arranging soil and water conservation practice properly. The mainly results of thisstudy are listed as below:(1) This study discussed the effects of erosion power, soil properties, and croproot on soil detachment capacity. The results indicated that soil detachment capacitylinearly increased with increasing shear stress. With increasing soil cohesion,water-stable aggregate and crop root density, soil detachment capacity reduced as anexponential function.The temporal variations of soil detachment capacity were affected by tillagepractices, soil consolidation, water-stable aggregates, and root growth. Soildetachment capacity for each crop fluctuated significantly over time with a similarpattern of the temporal variation following increased firstly, then decreased (p <0.05)during one growing season in the Loess Plateau. The measured mean Dcwas greatestfor potato (1.57±1.4kg m-2s-1), followed by maize (1.37±1.34kg m-2s-1), soybean(1.21±1.30kg m-2s-1), and millet (1.15±1.31kg m-2s-1).(2) This study revealed the temporal variation in soil rill erodibility and itsinfluencing factors. The decline of soil rill erodibility could be explained by theincreasing of crop root density, bulk density, and soil cohesion using an exponentialfunction. Soil rill erodibility for each crop fluctuated significantly over time with asimilar pattern of the temporal variation following increased firstly, then decreasedduring one growing season in the Loess Plateau (p <0.05). The measured mean Krwas greatest for potato (0.17±0.14s m-1), followed by maize (0.15±0.13s m-1),soybean (0.13±0.13s m-1), and millet (0.12±0.13s m-1).(3) This study revealed the temporal variation in soil critical shear stress and itsinfluencing factors. No significant temporal variation in soil critical shear stress foreach crop was found during one growing season（pï¼0.087，0.158，0.608，0.897）following the temporal variation of soil cohesion, bulk density, water-stableaggregates, and root growth. Further studies are needed to investigate the potentialeffects of soil properties and root growth on critical shear stress.(4)The prediction model of soil detachment capacity and soil rill erodibilitybased on shear stress, soil cohesion, and root density were established（NSE0.89， NSE≥0.82）. The prediction model of soil critical shear stress based on soil cohesionand root density was established（0.51≤NSE≤0.84）. |
