Simulation of the landform change process on a purple soil slope due to tillage erosion and water erosion using UAV technology

Both tillage erosion and water erosion are severe erosional forms that occur widely on sloping agricultural land.However,previous studies have rarely considered the process of landform change due to continuous simulation experiments of alternating tillage erosion and water erosion.To identify such changes,we applied a scouring experiment(at a 60 L min-1 water discharge rate based on precipitation data from the local meteorological station and the catchment area in the Yuanmou County,Yunnan Province,China)and a series of simulated tillage experiments where plots were consecutively tilled 5,10,and 15 times in rotation(representing 5 yr,10 yr,and 15 yr of tillage)at slope gradients of 5°,10°,and 20°.Close-range photogrammetry(CRP)employing an unmanned aerial vehicle(UAV)and a real-time kinematic global positioning system(RTK-GPS)was used to measure landform changes,and highresolution digital elevation models(DEMs)were generated to calculate net soil loss volumes.Additionally,the CRP was determined to be accurate and applicable through the use of erosion pins.The average tillage erosion rates were 69.85,131.45,and 155.34 t·hm-2·tillage pass-1,and the average water erosion rates were 1892.52,2961.76,and 4405.93 t·hm-2·h-1 for the 5°,10°,and 20°sloping farmland plots,respectively.The water erosion rates increased as tillage intensity increased,indicating that tillage erosion accelerates water erosion.Following these intensive tillage treatments,slope gradients gradually decreased,while the trend in slope gradients increased in runoff plots at the conclusion of the scouring experiment.Compared to the original plots(prior to our experiments),interactions between tillage and water erosion caused no obvious change in the landform structure of the runoff plots,while the height of all the runoff plots decreased.Our findings showed that both tillage erosion and water erosion caused a pseudo-steady-state landform evolutionary mechanism and resulted in thin soil layers on cultivated land composed of purple soil in China.

The regional difference in engineering-control and tillage factors of Chinese Soil Loss Equation

Accurate assessment of soil erosion is an important prerequisite for controlling soil erosion.The engineering-control(E)and tillage(T)factors are the keys for Chinese Soil Loss Equation(CSLE)to accurately evaluate water erosion in China.Besides,the E and T factors can reflect the water and soil conservation effects of engineering-control and tillage practices.But in the current full coverage of soil erosion surveys in China(such as soil erosion dynamic monitoring),for the same practice,the E or T factors are assigned the same value across the country.We selected 469 E and T factors data based on runoff plots from 73 publications,and they came from six soil and water conservation regions.Correlation analysis,regression analysis,and nonparametric tests were used to determine the comparability of the data,and it was proved that the runoff plots dimensions are consistent with the local topography.The results of one-way ANOVA and nonparametric tests for E and T factors in different regions showed that the engineering-control practices have good soil and water conservation effects and weaken the regional differences of other environmental factors,so there were no significant differences in E factors between different regions.However,there were significant differences in T factors between different regions,and the geodetector was applied to explore the intrinsic driving force of the spatial distribution of T factors.The results of the geodetector showed that the dominant driving forces of the spatial distribution of different types of tillage practices were not completely the same.When using CSLE to calculate water erosion,the E factor of the same practice can be used uniformly throughout the country,and the T factor needs to be considered and selected according to regional differences.At the same time,when choosing tillage practices in each water and soil conservation region,practices with better sediment reduction benefits should also be selected according to the regional environmental conditions.

STUDIES ON FOREST WATER CYCLING

Principal ideas, research approaches and installations in both Liangshui and Maoershan Ecological Stations were diseussed. Significance of comparability and synchronous detennination in research methods were stressed. Comparison analysis was done on the results gained from diferent methods. Adaptive mechanisms of Mongolian oak (Quercus mongolica) to drought and unproductive sites wer expounded through hydrological cycling studies. Surface runoff and flood peak were decreased and the developing processes of flood peak were postponed or delayed because of the presence of huge forest canopy and forest floor. However, the conclusions of forest influences on total runoff,especially in spring and in the dry season t are significant to agricultul practices in notheast China and turned out contrary for satershed sizes or different approaches, which should be studied further.

Effect of Eucalyptus expansion on surface runoff in the central highlands of Ethiopia

Introduction:Land use/land cover change can affect the ecological processes of an area such as hydrological cycle.The change in the condition of water resources of an area could be a good indicator of changes in ecosystem function as a result of altered land use/land cover.Eucalyptus expansion in central Ethiopia is one of the recent land use/land cover changes causing controversy on its potential ecological effect.This study was designed to evaluate effects of three adjacent land uses/land covers,i.e.cultivated land,grassland and Eucalyptus woodlot on surface runoff in Meja River watershed,central Ethiopia.Methods:The rainfall amount at each study catchment was collected using the rain gauge installed to record daily rainfall amount.The three land use/land cover types in each study catchment were selected for comparison as treatments.Four replications of each land use/land cover were used forming a total of 12 runoff plots.The rainfall and runoff data were collected twice a day for 91 days.Results:The study found that land use/land cover significantly affects surface runoff generated from the plots.Higher runoff was recorded from cultivated land.There was no significant difference on runoff volume between grassland and Eucalyptus woodlot.Conclusions:This shows that expansion of Eucalyptus on grassland could not have significant impact on surface runoff generation but if planted on previously farmland could reduce surface runoff.

Measurement errors on sediment concentration from traditional runoff collection tanks and its correction possibility

Runoff plots are widely used worldwide to monitor water and soil losses.Sediment concentration in runoff collection tank is measured by stirring-sampling procedure,but this method may produce high measurement error due to the uneven mixing of collected sediments with water and soil particle deposition.This study aimed to identify the relationship between actual and measured sediment concentrations,so as to estimate the systematic error of sediment concentration measurement from runoff collection tank by traditional stirring-sampling procedure and the possibility to eliminate it.Four major soils including black soil,silt loess,clay loess,and purple soil in China were used to determine the correlation between the measured and designed sediment concentrations in laboratory.Tested sediment concentration was 1,2,5,8,10,20,50,80,100,200,500,800,and 1000 kg/m^(3),and total sediment-laden water volume was 50 L and 100 L.Five samples were collected successively from collection tank for each treatment and their sediment concentrations were measured by conventional oven-drying method.The results showed that all the measured sediment concentration values were smaller than the designed ones,but both the measured and designed values were linearly correlated significantly with determination coefficients greater than 0.8,generally.In the whole tested concentration range,the systematical error was-0.19 to-319.95 kg/m^(3) and relative error was 0.30%-84.5% for the 4 tested soils and 2 total sediment-laden water volumes.These results indicated a necessity and possibility to correct conventional sediment concentration measurement value.The result is usable to assess and correct the measurement error of sediment concentrations from traditional runoff plot.