Ein Vergleich deutscher und schweizerischer Regensimulatoren nach Regenstruktur und kinetischer Energie

Comparison of German and Swiss Rainfall Simulators - Rain Structure and Kinetic Energy The drop size distributions of the investigated rain are significantly different. The rainfall simulators Swanson, Bonn, Basel and Trier culminate in the 2 - 3 mm drop diameter class (～40%) and thus simulate best the drop size distribution of natural heavy rainfall. The structure and the kinetic energy of the rains of eight rainfall simulators have been investigated. The data are compared to those registered during a thunder-shower at the research station of Mertesdorf near Trier/FRG. The results are summarized as follows:

• The impact velocity of artificial raindrops depends on the water pressure within the rainfall simulator, the initial velocity of the raindrops and the fall height. A correction factor to match the kinetic energy of natural rainfall, which is based on the percentage of deviation from the terminal velocity, can be applied only to some extend.
• With respect to various fall velocities of the artificial raindrops all tested rainfall simulators except one yield a rainfall energy between 19 and 27 J/m² per mm of rainfall.
• The actual amount of precipitation measured at the end of the rainfall experiments sometimes differs significantly from the aimed value of 60 mm/h. Due to this variation, the total rainfall energy during the experiments accumulated to 9 - 15 MJ/ha.
• This high variability depends on the used rainfall simulator. But it also demonstrates the importance of precipitation measurements on the plot during simulations in order to exactly calculate the rainfall energy.

     

Comparison of German and Swiss Rainfall Simulators - Influence of Plot Dimensions

The construction and operation of a rainfall simulator becomes easier with decreasing plot size. We studied the effect of plot size on the erosion dynamics and whether it is preferable to decrease plot width or plot length. 22 simulated rainfalls were carried out with Veejet 80 100 simulators and on plots of considerably differing dimensions. The plot width has to cover a representative width of the field. With the common 3 m wide farm machinery, a plot width of at least 1.5 m containing one wheel track is necessary. Narrower plots are not suited for erosion experiments on agricultural land. The influence of plot length can be described with the LS factor of the USLE down to a plot length of 4.5 m and with the RUSLE for interrill plots (0.75 m). With decreasing plot size, the runoff started later (up to 20 min) and the afterflow ended earlier. This is not only a result of the plot length (r = 0.78), but mainly of the plot size (r = 0.92). The large time lag on small plots complicates the interpretation of the results. We recommend to disregard the rain erosivity during the time lag for the determination of USLE parameters. This is in accordance with the procedure of Wischmeier & Mannering (1969). Plot sizes have to be selected particularly carefully if the fate of soluble substances is to be studied.     

Comparison of German and Swiss rainfall simulators - Relative drop energies and their distribution in time and space for simulated rains

Using a drop impact transducer, the relative energy and distribution of rains simulated by five different field simulators at almost the same rainfall intensity were monitored along runoff plots. Evaluation of the impact pulses registered with a highly-resolving X-t-recorder indicated that the rainfall energies of all simulators varied with time and position. Despite this variability, in many cases differences between the different rainfall simulators were significant. It was also found that the energy of one simulator was not typical for natural rainstorms and that that of another one was sensitive to wind conditions. Rainfall simulators with moving nozzles as dropformers showed characteristic periodicities in their energy distribution.     

降雨因子对沂蒙山区不同土地利用方式径流小区产流产沙的影响

[目的]研究降雨量、降雨强度、降雨历时等降雨因子对沂蒙山区小流域不同土地利用方式径流小区产流产沙的影响,为该区水土流失防治、水土保持规划、生态建设等提供参考。[方法]对沂蒙山区不同土地利用方式径流小区(自然荒坡和荞麦、野生牧草和花生)两两对照并且进行连续3a的定位观测,对观测数据进行统计分析和显著性检验。[结果](1)降雨量与各径流小区产流量的相关性显著(p0.01),与荞麦小区和花生小区产沙量的相关性显著(p0.01),与自然荒坡小区和野生牧草小区的产沙量相关性较差。(2)平均降雨强度(I)与各径流小区的产流量和产沙量的相关性均不显著。10 min最大降雨强度(I10)和30min最大降雨强度(I30)与各径流小区产流量以及荞麦小区、花生小区的产沙量均具有较好的相关性,其中30min最大降雨强度(I30)的相关性最好。(3)降雨历时与荞麦径流小区的产流量和产沙量相关性显著(p0.01),与其他径流小区的产流量和产沙量虽皆呈正相关但相关性均不显著。[结论]降雨量(P),10min最大降雨强度(I10),尤其是30min最大降雨强度(I30),降雨历时等降雨因子在沂蒙山区坡面产流产沙过程中都起到了不同程度的作用,不同的土地利用方式也是影响坡面产流产沙的重要因子。     

Using meshes to change the characteristics of simulated rainfall produced by spray nozzles

Rainfall simulators have been used for many years contributing to the understanding of soil and water conservation processes. Nevertheless, rainfall simulators’ design and operation might be rather demanding for achieving specific rainfall intensity distributions and drop characteristics and are still open for improvement. This study explores the potential of combining spray nozzle simulators with meshes to change rainfall characteristics, namely drop properties (drop diameters and fall speeds). A rainfall simulator laboratory set-up was prepared that enabled the incorporation of different wire meshes beneath the spray nozzles. The tests conducted in this exploratory work included different types of spray nozzles, mesh materials (plastic and steel), square apertures and wire thicknesses, and positions of the meshes in relation to the nozzles. Rainfall intensity and drop size distribution and fall speed were analysed. Results showed that the meshes combined with nozzles increased the mean rainfall intensity on the 1 m² control plot below the nozzle and altered the rain drops’ properties, by increasing the mass-weighted mean drop diameter, for example.     

坡度与种植方式对紫色土侵蚀与养分流失的影响研究

在涪陵区水土保持监测分站内建立6个径流小区,对紫色土坡耕地水土流失进行试验监测,结果表明:各小区径流量、产沙量总体随降雨量的增大而增大.自然生态修复措施防治水土流失效果显著,3.66 m3的径流量仅有0.41 kg·m3的产沙量,可有效防治紫色土坡耕地的水土流失.采用顺坡耕作措施的小区径流量与降雨量达显著正相关,而产沙量与降雨量未显著相关.径流量和产沙量大小顺序均为25°坡耕地>20°坡耕地>10°坡耕地>15°坡耕地,在15°耕地上径流量与产沙量均为最小,但15°是否是涪陵区最适宜的耕地坡度,仍有待今后收集更多的降雨资料加以分析说明.对一次强降雨进行养分流失观测,养分流失量与径流量及产沙量大小顺序基本一致.开发建设项目弃土弃渣监测点径流量与产沙量均大大高于其他小区,说明开发建设水土保持项目中防治水土流失的重要性.     

黔西北乡土植物篱对典型石漠化区石灰土侵蚀动力学过程的调控

在自然降水条件下,定量研究黔西北喀斯特石漠化区典型乡土植物刺梨在坡耕地产流产沙的变化规律,分析该植物篱控制侵蚀产沙的水动力学机理。结果表明,刺梨植物篱截流、分流作用延缓径流产生及汇流时间,增加喀斯特坡面径流入渗量,减小坡面侵蚀动力。在不同降雨强度条件下,喀斯特坡面入渗率与径流量和产沙量呈负线性相关。植物根系缠绕串连黏结根土,改变土壤的入渗特性,增强土壤抗冲性与抗蚀能力。根系密度随土层深度增加而减少,减沙效应亦变小。土壤抗侵蚀能力与d<1mm的须根密度呈极显著正相关关系,与d≤2mm须根的根量、根长与土壤抗冲指数存在线性回归关系。当I30雨强为2.41mm时,植物篱小区几乎无流水侵蚀,而对照样地侵蚀产生较多泥沙;当I30为4.72,8.35mm时,研究小区皆已侵蚀产沙,并在对照样地侵蚀产生细沟,显示雨强加大,坡面产流动力加强,冲沙携沙能力加大。说明植物篱起到保水固土减沙和对土壤侵蚀水动力过程的调控。喀斯特坡面流侵蚀产沙水动力主要受降雨强度和雨滴动能影响,雨滴侵蚀力的大小取决于雨量、雨强、雨滴大小。侵蚀产沙量与雨强、降雨历时呈显著的幂函数关系。揭示了植物根系固土减沙和提高土壤抗侵蚀水动力的调控机理。     

A new splash cup to measure the kinetic energy of rainfall

Splash cups have long been successfully used for both the quantification of kinetic energy of rainfall and the detachability of soil particles by rainfall impact, the so‐called “splash erosion”. Measurements of kinetic energy, however, have been difficult to operate in the field especially in remote areas, on steep slopes, and in forests since boundary conditions need to be controlled precisely. This paper introduces a new splash cup based on Ellison's archetype that reliably and accurately measures kinetic energy as a function of sand loss under a large variety of conditions. The Tübingen splash cup (T splash cup) is relatively easy to operate under harsh field conditions, and it can be used in experimental designs with a large number of plots and replications at reasonably low costs. The cup is constructed from plastic laboratory flasks and plastic pipes from water‐supply equipments. The unit sand is held by a removable carrier system that can easily be replaced in the field. The splash cups have been calibrated in combination with a laser distrometer using a linear regression function with r² = 0.98. They measure kinetic energy over a wide range of rainfall intensities from 0.6 to 40 L m^–2 h^–1. Kinetic energy per area varies between 10 and 250 J m^–2. Two years of field test measurements in a subtropical forest ecosystem in China proved the reliability, durability, and usability of our new splash cups and allowed detecting differences in kinetic energy between different tree species and biodiversity levels.     

Comparison between rainfall simulator erosion and observed reservoir sedimentation in an erosion-sensitive semiarid catchment

Estimating catchment scale soil loss based on rainfall simulators is often hampered by the difficulty to scale up simulator results. Our objective was to develop and test a method for estimating catchment scale soil loss based on observed rainfall using a variable intensity rainfall simulator in an erosion-sensitive catchment in semiarid Tunisia. A 7-year period, 1992–1999, with observed sedimentation amounts in a downstream reservoir was chosen to test a methodology. The methodology was based on (1) energy adjustment for the used simulator due to the difference in kinetic energy of simulated and natural rainfall at equal intensities and (2) upscaling of simulated erosion in which rill erosion was estimated by adjusting the difference between slope lengths for the plots versus the catchment after onset of runoff. The comparison between calculated soil loss from rainfall simulator experiments and observed sedimentation in the downstream reservoir displayed good overall results. Calculated soil loss was found to be about 96%, 36%, and 80% for different observed subperiods, respectively. The observed low value for the second period was probably due an exceptionally intense rainfall event during this period, which appears to have led to gully erosion, soil slide, and riverbank collapse. Therefore, during this event, siltation in the reservoir may essentially be due to unaccounted erosion processes such as gully erosion. Overall, however, it appears that plot-scale variable intensity rainfall simulators can rather successfully estimate catchment scale soil losses.     

黄土丘陵区不同坡度、土地利用类型与降水变化的水土流失分异

 为了确定不同坡度、土地利用类型及降水参数对水土流失的影响,通过黄土丘陵区坡耕地、草地的3个坡度(10°,15°和20°)小区连续14年的径流、侵蚀观测数据,分析不同坡度、土地利用模式和降水变化的水土流失分异。试验结果表明:1)坡耕地水土流失量随坡度的升高而增加,20°小区显著大于10°和15°小区;草坡地小区的年水土流失量也随坡度变化,不同坡度小区之间没有显著性差异。2)坡耕地与草地的水土流失量具有显著性差异,坡耕地年均径流量和侵蚀量分别为草地的1．8倍和13．9倍,与草地比较,坡耕地明显地增加水土流失风险。3)不同土地类型水土流失模数受年降水变化的影响效应不同。坡耕地水土流失量受少数强降水控制,年径流量、侵蚀量与年降水量、产流降水量之间无显著性相关;草地的年径流量、侵蚀量分别与年产流降水量、年降水量显著相关。4)坡耕地的水土流失受降水量(P)、最大30min降水强度(I30)和综合降水指数(PI30)的显著影响,但各因素的决定系数不同,影响系数次序为PI30>I30>P。草地的径流与降水变量关系与坡耕地一致,但次侵蚀量仅与I30变化的显著性影响,而与P、PI30无显著性相关。草地的水土流失量受坡度差异以及降水变化的影响较弱,表明草地能够有效地控制水土流失,对荒坡草地采取保护措施以促进植被、土壤的进展恢复。坡耕地水土流失变化与坡度、降水变量的关系更为直接,通过降低坡度、休耕和免耕等耕作模式,减少土壤扰动和增加地面植被盖度,可有效减少水土流失。     

A mathematical model for evaluating the effect of wind on downward-spraying rainfall simulators

Rainfall simulators are used to study a variety of different processes (e.g., water erosion, infiltration, overland flow, irrigation, movement of agrochemicals, etc.). Wind affects field experiments that make use of rainfall simulators. Water-drop trajectories and velocities are altered, affecting water application and kinetic energy distributions.In this study, a three-dimensional numerical model was developed from the movement of individual drops after their release from the nozzle of a downward-spraying rainfall simulator. Drag forces, wind and gravity affect the original momentum of a single drop. Water application and kinetic energy were estimated from the coupling of a hydrodynamic model for drop movement, a drop generator representing a single full-cone spray nozzle, and an appropriate interception algorithm at the soil surface.The mathematical model should facilitate the selection of single full-cone spray nozzles and the size and configuration of the spray area for rainfall simulation in order to achieve high application uniformity values on the plot area. It can contribute to the adequate choice of nozzles as well as operating conditions necessary for laboratory and field purposes. Laboratory and field experiments were conducted to evaluate the adequacy of the proposed methodology.     

Frequency of defoliation and nitrogen and phosphorus fertilization on Andropogon gayanus Kunth. I. Yield,crude protein content,and in vitro digestibility

Abstract

An experiment was conducted in a semi‐arid region located in the State of Zulia, western part of Venezuela (10°32'N and 71°42'W, 600 mm average annual rainfall), to evaluate dry matter (DM) yield and in vitro organic matter digestibility (IVOMD), and crude protein (CP) content of Andropogon gayanus Kunth as affected by three frequencies of defoliation (every 42, 63, and 84 days) and fertilization with three levels of nitrogen (N) (0, 100, and 200 kg N ha^‐1‐year^‐1) and two levels of phosphorus (P) (0 and 75 kg P₂O₅ ha^‐1.year^‐1) in a factorial array using a split‐split‐plot experimental design with frequencies in the main plots, N in the sub‐plots, and P in the sub‐subplots with three replications. Soil was a sandy loam Aridisol with a pH of 5.5. Average soil calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), and P contents were 0.6, 0.3, 0.1 and 0.17 meq‐100g^‐1 soil, and 6 ppm, respectively. Data from six, four, and three cuttings for the frequencies of 42, 63, and 84 days were analyzed over the total duration of the study (252 days) as well as separately for periods with high (168 days, 384 mm) and low rainfall (84 days, 69 mm). Frequency of defoliation was the only factor that influenced (P≤0.05) the variables studied. In the overall analyses, the highest (P≤0.05) DM yield (3,656 kg#lbha^‐1.cutting^‐1) was obtained with harvests every 63 days. Mean IVOMD decreased (P≤0.05) from 54.2 to 51.7% with increasing harvest interval from 63 to 84 days, respectively. The average CP content was 7.9%. With low rainfall, mean DM yield was 2,209 kg#lbha^‐1, CP content declined (P≤0.05) from 7.5 to 3.9% as the cutting interval increased, and IVOMD decreased (P≤0.05) between 42 and 63 days. With high rainfall, the highest (P≤0.05) DM yield (4,872 kg#lbha^‐1) and IVOMD (56.5%) were found at 63 days of age. Mean CP content was 9.3%. These results confirm that A. gayanus is a highly productive forage grass. Lack of response to N and P fertilizers may be attributed partly to relatively low rainfall during the experiment, adaptation of the grass to low fertility soils, and long intervals between N applications and the next harvest.     

Interrelationship among slope steepness,tillage practice and rainfall properties with surface runoff and soil loss on Mollisols in Northeast China

ABSTRACT

Soil erosion and rainfall-induced runoff are well studied yet remain somewhat unpredictable from one natural rainfall to the next, due to interactions between erosion parameters. This study quantified the relationship between annual (2011–2016) and individual (2016) rain events with overland flow (runoff) and soil loss in China’s northern ‘corn-belt’. Two tillage practices and slopes were evaluated (no-till and conventional till, 5° and 7° slopes). Results showed 54 rainfall events for a total of 394 mm precipitation ranging between May and October 2016. Runoff occurred 13 times in the conventional till with 7° slope, accounting for 25.9% of the precipitation volume and caused 15.6 t ha^?1 erosion. It occurred twice in the no-till with 5° slope plot and caused 0.2 t ha^?1 erosion., Thus the no-till with 5° slope treatment is the best tillage system to protect soil in Mollisols in Northeast China. Broad analysis coupled with a detail review of three rainfall events demonstrates that water either runs off plots quickly or rapidly infiltrates while sediment moves in a pulsing manner.     

Comparison of German and Swiss Rainfall Simulators - Accuracy of Measurement and Effect of Rainfall Sequence on Runoff and Soil Loss Rates

An important characteristic of the suitability of a specific rainfall simulator is the accuracy that can be obtained in measuring runoff rate, sediment concentration and soil loss rate. The accuracy of the different simulators currently in use in Germany and Switzerland was determined. The simulators differed greatly in the accuracy of sediment concentrations, runoff rates and soil loss rates they produced. Major sources of error were small plot sizes and wind drift. However, most of the simulators were suitable for erosion research (Average confidence interval: 30%). The time measurement of the runoff rates limits the accuracy of the best measuring method actually available. The smallest increment that can be measured during a run is one second. With high runoff rates, rounding to the next full second can cause the runoff rate to alternate by 10%. In erosion experiments, a sequence of rains is often applied on a plot to examine different soil conditions. Several sequences are in use. To facilitate comparison of the sediment concentration, runoff rates, and soil loss rates obtained with different sequences, it was concluded that the total rain duration should at least be 90 minutes and that the first run should last at least one hour. Therefore, a sequence is recommended that has a 1 h first run, a 0.25 h break and a 0.5 h second run. Sequences with a second and third run on the following day are disadvantageous in most cases.     

Vergleich deutscher und schweizer Regensimulatoren - Einfluß der Regeneigenschaften auf die Bodenoberflächenrauhigkeit

Comparison of German and Swiss Rainfall Simulators - Influence of Rainfall Characteristics on Soil Surface Roughness Six different field rainfall simulators were compared. Soil surface roughness was tested by a simple field method before and after rainfall simulation. Preparation of the test site with a rotary cultivator inadvertently entailed spatial variability of roughness and aggregate size. Thus, the plots with finer seedbed showed higher runoff and soil loss. The relative decrease of roughness could best be correlated with the total kinetic energy as well as with the R factor of the different simulators (r = 0.87 resp. 0.91). Thus, the degree of soil surface leveling was shown to be due to the rainfall characteristics of the different simulator types. However, there was no relation between change of soil surface roughness and runoff. The relative classification of the kinetic energy of the rainfall simulators explained the leveling of the soil surface better than the classifications previously used in many studies (r = 0.91 as against r = 0.73).     

Effects of agricultural practices on hydraulic properties and water movement in soils in Brittany (France)

The intensive agricultural use of soils in the Brittany region (western France) has increased the need for a better understanding of soil water dynamics. The aim of the present study is to compare quantitatively the differences produced by two agricultural practices on soil hydraulic properties (water retention curve and hydraulic conductivity) as well as the infiltration and drainage fluxes in the soils. This study was carried out on two experimental plots managed in the same way for 22 years. The two practices were continuous maize fertilized with mineral fertilizer, denoted as MX, and pasture within a ray-grass/maize rotation (3/1 year) with organic fertilization (pig slurry), denoted as PR. The study consisted of measuring soil physical properties in the laboratory and in the field, and estimating water infiltration in the soil of the two plots by recording water pressure heads after simulation of 2-h artificial rainfall with an intensity of 17 mm/h. We applied the van Genuchten model to describe the water retention and hydraulic conductivity curves (θ(h) and K(h)) for each soil horizon of the two plots. Hydrus-2D and ID softwares were used to construct a numerical model of water movement in the two soils. This model was used to quantify the infiltration rate, deep drainage and actual evaporation fluxes during the artificial rainfall experiment.The vertical influence of agricultural practices in both plots appears to be limited to the uppermost 35 cm. Deeper in the B horizon, there are only very slight differences in the hydraulic properties between the two plots. In the top soil horizons (H1–H5 and H6), the two soil properties mostly affected by practices are the hydraulic conductivity and the α parameter of the van Genuchten model. At the lowest pressure head studied here (−1.5 kPa), hydraulic conductivity in a given horizon differs by more than one order of magnitude between the two plots. The model reproduces quite satisfactorily the observed pressure heads in plot PR at all depths, in the rainy period as well as in the water redistribution period (efficiency >0.77). Results are less good for the MX plot, with efficiency ranging from 0.49 to 0.84 depending on the horizon. The different sources of simulation errors are identified and discussed. For the MX plot, the soil water movement model succeeds in reproducing the infiltration excess runoff observed in the field, allowing us to calculate that it accounts for 9% of the applied rainfall. No surface runoff or ponding appears in the PR plot during the artificial rainfall experiment. In the PR plot, the simulated deep drainage flux increases more rapidly than in the MX plot. The lower hydraulic conductivity in the top soil horizon of the MX plot compared with the PR plot appears to reduce the infiltration rate as well as the deep drainage flux. It also decreases the upward flow of water to the soil surface when the water content in the top soil layer is depleted by evaporation flux. The model simulation could be improved by a more precise representation of the soil structure, particularly the location, size and frequency of clods as well as the variability of hydraulic properties. However, we need to strike a balance between improving the quality of the simulation even further and the practical constraints and efforts involved in measuring the soil hydraulic properties.     

喀斯特坡地侵蚀性降雨阈值初探

喀斯特坡地表层岩溶带发育，入渗强烈，产流机制与非喀斯特坡地有较大差异，为提高喀斯特坡地土壤流失模型预测准确性，以贵州省普定县陈旗小流域6个不同土地利用类型径流小区为观测对象，分析2007—2010年、2015—2019年2期泥沙和地表径流数据，了解产流产沙规律，并利用降雨侵蚀力偏差法计算各小区侵蚀性降雨量。结果表明：(1)植被覆盖率与喀斯特坡地地表产流产沙量呈负相关，高植被覆盖下，暴雨和极端暴雨是造成喀斯特坡地水土流失的主要降雨事件；(2)植被恢复十余年随着覆盖度的提高，年均土壤流失量呈显著下降趋势，多小于10 t/km²;(3)喀斯特坡地裂隙发育，地下漏失严重，土壤量少且不易被侵蚀，除少数极端暴雨外，多数降雨不产流不产沙，因此建议将喀斯特坡地侵蚀性降雨量阈值定为50 mm,该阈值显著高于非喀斯特地区。     

Effect of Mulching with Vegetative Residues on Soil Water Erosion and Water Balance in an Oxisol Cropped by Cassava in East Cameroon

Soil water erosion is a major agricultural concern in tropical Africa with high precipitation and low soil fertility where Oxisols are generally distributed. A field experiment was conducted in east Cameroon during the rainy season in 2013 to investigate the effects of surface mulching with the residues of Imperata cylindrica on soil losses and surface runoff water generation in a cassava cropland on an Oxisol. Three treatments were established using two small plots for each treatment: bare plot (BA), cassava plot (CA) and cassava with mulch plot (CM). Soil loss and surface runoff water were measured, and water budgets of rainfall, surface runoff and soil moisture within rainfall events were measured in all treatment plots. Runoff coefficients in all treatment plots were suppressed below 8·0% because the large volume of large pores of surface soil of Oxisols contributed to the high drainage capacity over a rainy season even under wet soil moisture conditions. Total soil loss in CM was decreased by 49% compared with that in BA and CA, despite there not being a large difference in runoff water among treatments. These results suggest that surface mulching with the residues of I. cylindrica can substantially suppress soil losses caused by particle detachment by raindrops, while it maintain soil surface with originally high permeability in cassava croplands on Oxisols. Copyright © 2016 John Wiley & Sons, Ltd.     

东北薄层黑土区作物轮作防治坡面侵蚀的效果与C值研究

作物轮作通过影响通用土壤流失方程(USLE)中作物覆盖和管理因子C值的变化和改良土壤性质而减少坡面土壤侵蚀。基于东北薄层黑土区连续6年大豆—红小豆轮作和裸露休闲坡面小区的径流泥沙和降雨资料,分析了2011—2016年研究区侵蚀性降雨特征,探讨了作物轮作防治坡面土壤侵蚀的效果,研究了作物轮作C值的年内和年际动态变化。结果表明:研究区所有侵蚀性降雨皆发生在5—10月,其降雨量占全年降水量的32.5%～68.1%,且年内和年际分布不均。对于5°坡度的裸露小区,土壤侵蚀主要发生在6—8月,坡面径流量和土壤流失量分别为48.4mm和1 388.2t/(km~2·a);对于5°坡度的作物轮作小区,土壤侵蚀主要发生在5—7月,坡面径流量和土壤流失量分别为19.5mm和166.7t/(km~2·a)。与裸露休闲小区相比,作物轮作小区可使黑土坡面年径流量和土壤流失量减少59.7%和88.0%。大豆—红小豆轮作措施的多年平均C值为0.12,其中大豆作物的C值为0.04,变化范围0.007～0.080;红小豆作物的C值为0.38,变化范围0.28～0.46。大豆和红小豆作物的C值月变化分别为0.01～0.24和0.01～0.80,呈先减少后增加的变化趋势。大豆—红小豆轮作对东北薄层黑土区坡面土壤侵蚀防治有明显效果,研究结果可为薄层黑土区土壤侵蚀定量评价和预报模型的建立提供基础数据。     

汾河上游不同土地利用方式对坡地水土流失的影响

以汾河上游阳坡小流域为研究区,在2015—2017年进行了天然降雨条件下的坡面产流产沙小区试验,结果表明:(1)研究区的侵蚀性降雨在年内和年际间分布很不均匀。少数几次强降雨对降雨侵蚀力的贡献很大。(2)不同侵蚀性降雨条件下,鱼鳞坑+乔木或灌木拦蓄径流或泥沙能力最强,裸地最弱;坡面产流量大小依次为:裸地坡耕地草地油松黄刺玫鱼鳞坑+油松鱼鳞坑+黄刺玫。坡面产沙量大小规律为:鱼鳞坑+乔或灌草地乔或灌坡耕地裸地。(3)随着雨量增加,各植被小区的径流调控率和泥沙调控率均呈下降趋势;相近雨量时,随着雨强的增加,径流调控率和泥沙调控率明显下降。(4)各小区的降雨量和产流量、产流量和产沙量之间呈现显著正相关(P0.05)。在裸地、黄刺玫及草地小区,I30与产流量之间是均无显著相关。在裸地、油松、黄刺玫、耕地小区,I30和产沙量之间无显著相关。