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How to predict gully erosion rates was one of the most important issues at present. A model implemented in the Channel Hillslope Integrated Landscape Development (CHILD) model based on the shape factor (Sf) of the plunge pools, which successfully predicted the headcut retreat rates over a long timescale. But whether this model was also valid in the short-term scale? What factors affected the prediction effects of the model? These issues still need evaluation.
Material and methodFour gully head plots with consistent initial topography and soil types were constructed for conducting in-situ scouring experiments with different flow discharges. Eighteen tests were conducted in each plot to monitor the plunge pool growth and headcut retreat rates using an unmanned aerial vehicle (UAV) to create high-precision topographic data.
Results and discussionThe topographic parameters of the plunge pools generally increased with scouring duration and were strongly correlated with the total runoff energy consumption (0.55 < R2 < 0.92, P < 0.01). In contrast, headcut retreat was an intermittent process that suddenly migrated in a short time after relatively long stable periods lasting from 20 to 130 min. The relationships between the headcut retreat rates and total energy consumption were weaker than those with the plunge pools.
ConclusionAs the timescale shortened, the contribution of mass failure due to gravity to headcut migration significantly increased, leading to the pool effects of the model to influence the prediction of the gully headcut retreat rates, which assumed that flow hydraulics were the key dynamics.
相似文献Understanding the soil nitrogen (N) mineralization potential (N0) and crop N availability during the growing season is essential for improving nitrogen use efficiency (NUE) and preventing over-fertilization, which lead to negative environmental impacts.
MethodsFive black soils with different levels of fertility were selected in Northeast China. The N0 and kinetics of these soils were estimated through laboratory experiments at different incubation temperatures (15, 25, and 35 °C). N mineralization dynamics were simulated using field soil temperature according to the incubation results. Moreover, the N uptake dynamics of maize were simulated according to the literature.
ResultsCompared with the very low-fertility soils, the cumulative mineralized nitrogen increased under all incubation temperatures (15, 25, and 35 °C), by 48–136%, 8–61%, and 24–59%, respectively, in the medium- and high-fertility soils. The highest N0 values (96.90, 115.31, and 121.33 mg/kg at the three different temperatures) were recorded in the very high-fertility soils. The soil N mineralization dynamics and N uptake of maize in the growing season were highly consistent over time, although the soil N supply could not meet the maize growth requirements. The higher the soil fertility, the lower the N fertilizer requirement.
ConclusionsDifferent fertilizer strategies were developed based on the cumulative mineralized N, N uptake by maize, and NUE in soils with different fertility levels. We suggested a reduction of 50–65 kg N/ha in N fertilizer in the two highest fertility soils. This study provided basic data to reduce chemical N fertilizer to improve NUE and reduce negative environmental impacts.
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