Contrasted Impact of Land Abandonment on Soil Erosion in Mediterranean Agriculture Fields

Abandonment of agricultural land results in on-and off-site consequences for the ecosystem. In this study, 105 rainfall simulations were carried out in agriculture lands of the Mediterranean belt in Spain(vineyards in Málaga, almond orchards in Murcia, and orange and olive orchards in Valencia) and in paired abandoned lands to assess the impact of land abandonment on soil and water losses. After abandonment, soil detachment decreased drastically in the olive and orange orchards, while vineyards did not show any difference and almond orchards registered higher erosion rates after the abandonment. Terraced orchards of oranges and olives recovered a dense vegetation cover after the abandonment, while the sloping terrain of almond orchards and vineyards enhanced the development of crusts and rills and a negligible vegetation cover resulted in high erosion rates. The contrasted responses to land abandonment in Mediterranean agricultural lands suggest that land abandonment should be programmed and managed with soil erosion control strategies for some years to avoid land degradation.     

百喜草覆盖和敷盖对中国南方红壤坡地径流和产沙的影响

Rainfall,runoff (surface runoff,interflow and groundwater runoff) and soil loss from 5 m × 15 m plots were recorded for 5 years (2001-2005) in an experiment with three treatments (cover,mulch and bare ground) on sloping red soil in southern China.Surface runoff and erosion from the Bahia grass (Paspalum notatum Flugge) cover plot (A) and mulch plot (B) during the 5 years were low,despite the occurrence of potentially erosive rains.In contrast,the bare plot (C) had both the highest surface runoff coefficient and the highest sediment yield.There were significant differences in interflow and surface runoff and no significant difference in groundwater runoff among plots.The runoff coefficients and duration of interflow and groundwater runoff were in the order plot B > plot A > plot C.Effects of Bahia grass cover were excellent,indicating that the use of Bahia grass cover can be a simple and feasible practice for soil and water conservation on sloping red soil in the region.     

川中丘陵区人工刨地耕作方式下紫色土坡耕地侵蚀速率的137Cs和210Pbex双核素示踪法研究

Purple soils are widely distributed in the Sichuan Hilly Basin and are highly susceptible to erosion, especially on the cultivated slopes. Quantitative assessment of the erosion rates is, however, difficult due to small size of the plots of the manually-tilled land, the complex land use, and steep hillslopes. 137Cs and 210Pbex (excess 210Pb) tracing techniques were used to investigate the spatial pattern of soil erosion rates associated with slope-land under hoe tillage in Neijiang of the Sichuan Hilly Basin. The 137Cs and 210Pbex inventories at the top of the cultivated slope were extremely low, and the highest inventories were found at the bottom of the cultivated slope. By combining the erosion rates estimates provided by both 137Cs and 210Pbex measurements, the weighted mean net soil loss from the study slope was estimated to be 3100 t km-2 year-1, which was significantly less than 6930 t km-2 year-1 reported for runoff plots on a 10°cultivated slope at the Suining Station of soil Erosion. The spatial pattern of soil erosion rates on the steep agricultural land showed that hoe tillage played an important role in soil redistribution along the slope. Also, traditional farming practices had a significant role in reducing soil loss, leading to a lower net erosion rate for the field.     

Effect of vegetation changes on soil erosion on the loess plateau

Vegetation is one of the key factors affecting soil erosion on the Loess Plateau. The effects of vegetation destruction and vegetation restoration on soil erosion were quantified using data from long-term field runoff plots established on the eastern slope of the Ziwuling secondary forest region, China and a field survey. The results showed that before the secondary vegetation restoration period （before about 1866-1872）, soil erosion in the Ziwuling region of the Loess Plateau was similar to the current erosion conditions in neighboring regions, where the soil erosion rate now is 8 000 to 10 000 t km^-2 year^-1. After the secondary vegetation restoration, soil erosion was very low; influences of rainfall and slope gradient on soil erosion were small; the vegetation effect on soil erosion was predominant; shallow gully and gully erosion ceased; and sediment deposition occurred in shallow gully and gully channels. In modern times when human activities destroyed secondary forests, soil erosion increased markedly, and erosion rates in the deforested lands reached 10 000 to 24000 t km^-2 year^-1, which was 797 to 1682 times greater than those in the forested land prior to deforestation. Rainfall intensity and landform greatly affected the soil erosion process after deforestation. These results showed that accelerated erosion caused by vegetation destruction played a key role in soil degradation and eco-environmental deterioration in deforested regions.     

中国黄土高原丘陵沟壑区天然降雨下不同土地利用方式的水土流失效应

The Loess Plateau, which is located in the arid and semi-arid areas of China, experiences significant soil erosion due to intense human activities and soil erodibility. It is necessary to explore and identify the land-use types or land-use patterns that can control soil erosion and achieve certain agricultural production capabilities. This study established runoff plots with two slope gradients (5^O and 15^O) in north of Yan’an, one area of the Loess Plateau, with 3 single land-use types (cultivated land, CL; switchgrass, SG; and abandoned land, AL) and 2 composite land-use types (CL-SG and CL-AL). From 2006 to 2012, we continuously monitored the rainfall characteristics, runoff depth, soil loss, vegetation coverage, and soil physical properties. The results indicated a general trend in the number of runoff and soil loss events for the 5 land-use types: CL = CL-SG > CL-AL > SG> AL. The general trend for runoff depth, soil loss, their magnitudes of variation, and the slopes of rainfall-runoff regression equation was CL > CL-SG > CL-AL > SG > AL, whereas the rainfall threshold for runoff generation exhibited the opposite trend. Results of nonparametric test regarding runoff depth/EI₃₀ and soil loss/EI₃₀, where EI30 is the product of rainfall kinetic energy and the maximum rainfall intensity over 30 min, and the runoff depth-soil loss relationship regression indicated that the effect of CL-AL was similar to that of SG; SG was similar to AL; and CL-AL, SG, and AL were superior to CL with regard to soil and water conservation. Runoff depth and soil loss significantly increased as the slope gradient increased. Runoff depth and soil loss were significantly correlated with the soil particle size composition and bulk density, respectively. The strongest significant correlations were found between runoff depth and vegetation coverage as well as between soil loss and vegetation coverage, which showed that vegetation coverage was the primary factor controlling soil erosion. Therefore, the composite land-use type CL-AL and the artificial grassland (SG) are appropriate options because both soil conservation and a certain degree of agricultural production are necessary in the study area.     

中国黄土高原丘陵沟壑区天然降雨下不同土地利用方式的水土流失效应（英文）

The Loess Plateau,which is located in the arid and semi-arid areas of China,experiences significant soil erosion due to intense human activities and soil erodibility.It is necessary to explore and identify the land-use types or land-use patterns that can control soil erosion and achieve certain agricultural production capabilities.This study established runoff plots with two slope gradients(5°and 15°) in north of Yan'an,one area of the Loess Plateau,with 3 single land-use types(cultivated land,CL;switchgrass,SG;and abandoned land,AL) and 2 composite land-use types(CL-SG and CL-AL).Prom 2006 to 2012,we continuously monitored the rainfall characteristics,runoff depth,soil loss,vegetation coverage,and soil physical properties.The results indicated a general trend in the number of runoff and soil loss events for the 5 land-use types:CL = CL-SG CL-AL SG AL.The general trend for runoff depth,soil loss,their magnitudes of variation,and the slopes of rainfall-runoff regression equation was CL CL-SG CL-AL SG AL,whereas the rainfall threshold for runoff generation exhibited the opposite trend.Results of nonparametric test regarding runoff depth/EI_(30) and soil loss/EI_(30),where EI_(30) is the product of rainfall kinetic energy and the maximum rainfall intensity over 30 min,and the runoff depth-soil loss relationship regression indicated that the effect of CL-AL was similar to that of SG;SG was similar to AL;and CL-AL,SG,and AL were superior to CL with regard to soil and water conservation.Runoff depth and soil loss significantly increased as the slope gradient increased.Runoff depth and soil loss were significantly correlated with the soil particle size composition and bulk density,respectively.The strongest significant correlations were found between runoff depth and vegetation coverage as well as between soil loss and vegetation coverage,which showed that vegetation coverage was the primary factor controlling soil erosion.Therefore,the composite land-use type CL-AL and the artificial grassland(SG) are appropriate options because both soil conservation and a certain degree of agricultural production are necessary in the study area.     

不同土壤管理措施下基于水蚀过程的含沙量变异及其驱动

In order to prevent soil erosion in southern China, a study was performed to determine the drivers of sediment concentration variation using simulated rainfall and four soil management systems under field condition. Four soil management systems, i. e., forest and grass coverage (FG), forest coverage with disturbed soil surface (FD), contour tillage (CT) and downslope tillage (DT), were exposed to two rainfall intensities (40 and 54 mm h^-1) using a portable rainfall simulator. The drivers of sediment concentration variation were determined by the variations of runoff rate and sediment concentration as well as their relationships. The effects of the four soil management systems in preventing water and soil losses were compared using runoff rates and sediment concentrations at steady state. At runoff initial stage, sediment concentration variation was mainly driven by rainfall and management. The degree of sediment concentration variation driven by flow varied with different soil management systems. Three best relationships between runoff rate and sediment concentration were identified, i. e., reciprocal (CT), quadratic (FG and FD) and exponential (DT). At steady state, runoff rates of the four soil management systems varied slightly, whereas their sediment concentrations varied greatly. FG and CT were recommended as the best soil management systems for preventing water and soil losses.     

伊朗西北部半干旱农田径流模型的建立

Transformation of rainfall into runoff over an area is a very complex process which exhibits both temporal and spatial variability;runoff in a defined area can be affected by factors such as topography, vegetation, rainfall characteristics and soil properties. This study was conducted to develop an empirical model using the rainfall characteristics and soil properties for predicting runoff from dry-farming lands in a semi-arid agricultural area in Hashtroud, Northwest Iran. Runoff plots(1.83 m × 22.1 m) in triplicate were installed in thirty-six sloped dry-farming lands in the study area. Runoff under natural rainfalls was measured in each plot during a2-year period. The results showed that runoff for 41 runoff-producing rainstorm events with duration longer than 30 min was largely associated with a rainfall index obtained by multiplying the positive square root of rainfall depth(h0.5) by the logarithm of the maximum 30-minute intensity(LogI30)(R2= 0.81). Runoff significantly varied among the plots(P 0.001), which was considerably related to the effective soil properties(R2= 0.74), i.e., soil permeability(Per) and aggregate stability(AS). A multiple linear regression model was developed between runoff and the rainfall index(h0.5logI30) and the effective soil properties(AS and Per). Evaluation of the model using 34 runoff-producing rainstorm events that occurred during the next two years resulted in high values of the efficiency coefficient and R2(0.88 and 0.91, respectively), which revealed that the model developed in this study could be used in predicting runoff from the dry-farming lands in the semi-arid regions.     

中国云南滇池流域农田径流磷污染负荷影响因素研究

Effects of factors such as slope, surface soil texture, fertilization and crop cover with different rainfall intensities on phosphorus (P) losses in farmland runoff of the Dianchi Lake Watershed in Yunnan Province of China were studied through a rainfall simulation test using a red soil, one of the most widely distributed soils of the study area. Results showed that the runoff concentrations of total phosphorus (TP) and P losses differed with the slope, being highest when the slope was 18°. At two different rainfall intensities, the runoff TP and P losses had a similar decreasing trend as the surface soil texture became coarser, therefore applying the grit would decrease P in runoff from soils of farmland on slopes with heavier textures. With wheat as a crop cover the runoff TP concentrations and P losses were significantly lower than those of the bare soil. This showed that plant cover would greatly decrease P in runoff from the farmland of the study area. The TP concentration in runoff from the soil two days after fertilization doubled when compared with that from the non-fertilized soil, indicating that fertilization could mean a dramatic rise in P runoff if irrigation or heavy rainfall occurred immediately after application and that no fertilization before a rain and no irrigation immediately after fertilization would reduce runoff P loss from the farmland of the study area.     

中国滇池流域土地利用方式对土壤侵蚀和养分状况的影响

Soil erosion and loss of soil nutrients have been a crucial environment threat in Southwest China. The land use and its impact on soil qualities continue to be highlighted. The present study was conducted to compare soil erosion under four land use types(i.e.,forestland, abandoned farmland, tillage, and grassland) and their effects on soil organic carbon(SOC), total nitrogen(TN) and total phosphorus(TP) in the Shuanglong catchment of the Dianchi Lake watershed, China. There were large variations in the erosion rate and the nutrient distributions across the four land use types. The erosion rates estimated by137 Cs averaged 2 133 t km-2year-1under tillage and abandoned farmland over the erosion rate of non-cultivated sites, and the grasslands showed a net deposition. For all sites, the nutrient contents basically decreased with the soil depth. Compared with tillage and abandoned farmland, grassland had the highest SOC and TN contents within 0–40 cm soil layer, followed by forestland. The significant correlations between137 Cs, SOC and TN were observed. The nutrient loss caused by erosion in tillage was the highest. These results suggested that grassland and forestland would be beneficial for SOC and TN sequestration over a long-term period because of their ability to reduce the loss of nutrients by soil erosion. Our study demonstrated that reduction of nutrient loss in the red soil area could be made through well-managed vegetation restoration measures.     

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。     

江西丘陵红壤区坡面径流及其与降雨关系的影响因素

通过径流小区方法,对比观测了采取提高植被盖度,改顺坡耕作为横坡耕作,改直坡为梯田,地表覆盖死地被物4类治理措施9个不同小区地表径流量和同期降雨特征。在比较不同小区地表径流量的基础上,分别建立降雨量、降雨强度、降雨历时与地表径流量回归方程,分析了各种措施对于降雨径流相关性的影响。（1）采取4类措施后,地表径流量显著减少;（2）4种措施对于地表径流与降雨关系的影响存在相同趋势,即措施在降低地表径流量的同时,提高降雨量、降雨历时与地表径流量的相关性,降低降雨强度与地表径流的相关性。在耕作方式对比试验中．横坡耕作与顺坡耕作相比．在减少地表径流的同时,降雨强度与径流量相关性略有提高。地表覆盖和耕作措施在降低地表径流量的同时．也降低了降雨历时与地表径流相关性。     

丘陵半干旱区小流域入渗产流特征研究

为了探索我国丘陵半干旱区小流域入渗产流规律,为该地区雨水径流集蓄利用和区域生态环境治理提供依据,通过人工模拟降雨和自然降雨入渗产流试验,对小流域坡耕地、林地、草地和荒地的降雨入渗产流特征进行了系统研究。结果表明,农林草地比荒地具有明显的拦蓄地表径流和减少土壤侵蚀的效果,比荒地拦蓄地表径流效率增加35.7?.0%,拦蓄泥沙效率增加46.2?.6%;利用Philip入渗理论和逐步回归分析方法对入渗产流试验结果处理分析,建立了小流域坡耕地、林地和荒地土壤的入渗产流及其相关因子数学模型;小流域产流系数与降雨小区地形坡度、降雨强度、植被盖度、土壤雨前含水量和土壤孔隙度等因子显著相关。     

保护性耕作对农田地表径流与土壤水蚀影响的试验研究

在黄土坡地建立天然降雨径流小区,采用翻斗式自动测试系统同步动态地监测降雨—径流的过程,试验研究了保护性耕作农田水土保持的效果和耕作、覆盖及压实3种因素对农田水土流失的影响。2年的试验表明,雨强和雨型与坡地水土流失密切相关,在暴雨情况下,由秸秆覆盖与少免耕相结合的保护性耕作具有明显的保持水土作用;采用少免耕而无秸秆覆盖配合的情况下,水土流失甚至高于传统翻耕。在试验的6种处理中,免耕覆盖不压实的保水保土效果最佳,相对传统翻耕年径流量减少52.5%,年土壤流失量减少80.2%。在覆盖、压实及耕作3因素中,秸秆覆盖对保持水土的作用最大,可减少年径流量47.3%,减少年土壤水蚀77.6%;压实次之,地表耕作的影响较小。     

Runoff generation in a degraded Andean ecosystem: Interaction of vegetation cover and land use

Tropical mountain regions are affected by rapid land use/-cover change, which may threaten their (eco-)hydrological functions. Although there is a growing interest in evaluating the effect of land use/-cover change on mountain hydrology, quantitative assessments of the impact of land use/-cover on hydrological processes are hampered by the lack of field measurements characterizing runoff generation processes. In this paper, we present results from field experiments of rainfall runoff mechanisms in the southern Ecuadorian Andes. A rainfall simulator was used to quantify the hydrological response of distinct land use/-cover types to intense rainfall (about 40 mm/h). The rainfall runoff experiments indicate that degraded and abandoned land generate surface runoff within a few minutes after the start of the rainfall event. These lands have a very rapid and sharp hillslope hydrological response, as Hortonian overland flow is the dominant runoff generation mechanism. In contrast, surface runoff on arable and rangelands is rare, as their soils are characterized by a high infiltration capacity (i.e. > 29 mm/h). Our experiments provide evidence that runoff generation in degraded Andean ecosystems is mainly controlled by the surface vegetation cover and land management. When reducing the surface vegetation cover, the soil is increasingly affected by rapid hillslope runoff as the presence of large amounts of smectites in the outcropping soft rocks makes the material very prone to sealing and crusting, thereby enhancing runoff generation.     

晋西黄土丘陵沟壑区水平阶造林减水减沙效益研究

利用人工模拟降雨装置,对水平阶林地、梯田、坡耕地在百年一遇暴雨下的产流产沙规律进行了试验研究。研究结果表明,与陡坡耕地相比,坡耕地退耕实施水平阶整地造林后,可减少径流８７５％,减少土壤侵蚀９９７％,径流深与降雨历时之间存在着很好的对数函数关系。     

Repeated measurements on permanent plots using local variability sampling for monitoring soil cover

On US military installations, training activities such as vehicle use disturb ground and vegetation cover of landscapes, and increase potential rainfall runoff and soil erosion. In order to sustain training lands, soil erosion is of major concern. Thus there is a need for sampling designs to monitor degradation and recovery of land conditions. Traditionally, permanent plots are used to obtain the change of land conditions. However, the permanent plots often provide less information over time in characterizing the land conditions because of the fixed number and locations of plots. In this paper, we analyzed the sufficiency of a permanent plot sample and developed a method to improve the re-measurements of the permanent plots over time for a monitoring system of soil erosion based on spatial and temporal variability of a random function. We first applied a local variability based sampling method to generate reference samples that have sampling distances varying spatially and temporally to monitor a soil erosion relevant cover factor for an installation, Fort Riley, USA. Then, we compared a permanent sample with the reference samples annually over 13 years to determine additional sampling in the areas with high variability and temporarily suspending measurements of the permanent plots in the areas with low variability. The local variability based sampling provides estimates of local variability of the cover factor and thus is more cost-efficient than random sampling. By comparison with a reference samples, the re-measurements obtained should more accurately characterize the dynamics of the land conditions.     

南方红壤区植被结构类型与降雨模式对林下水土流失的影响

植被和降雨是水土流失的关键因素,探究二者对水土流失的影响对开展水土保持具有重要意义。该研究基于鹰潭红壤生态试验站5种植被结构类型的径流小区2016-2018年93次降雨、径流、泥沙观测资料以及各小区植被结构参数,利用自组织映射(self-organizing maps,SOM)方法,根据雨量、历时、60 min最大雨强、平均雨强、降雨集中性等特征指标划分降雨模式,研究了不同降雨模式和植被结构类型的水土流失特征,并采用冗余分析(RDA)定量研究降雨与植被对林下水土流失的影响。结果表明,SOM方法能客观识别红壤区4种典型侵蚀降雨模式,R_Ⅲ模式(短历时、大雨强、雨量集中)是造成水土流失的主要降雨模式,R_Ⅳ模式(多雨量、大雨强、长历时)最具侵蚀性破坏力;植被结构类型显著影响水土流失,水土保持功能从大到小依次为:灌草混交林、草地、低灌林、乔木林、高灌林。RDA分析表明,降雨模式与植被结构类型能够改变降雨、植被对水土流失的影响,随着降雨模式由弱到强转变,植被的水土保持功能逐渐减小,降雨影响增强,水土流失由植被主控演变为平衡控制、降雨主控;随着植被结构类型由近地表植被向灌木、乔木的变化,植被的调节能力减小,降雨影响增强。     

黄土区不同土地经营方式径流量神经网络模拟

基于黄土坡面降雨—径流关系的复杂性和非线性,引用3层前馈型BP网络模型,对不同土地经营方式(草灌地、刈割地、翻耕地)径流量进行模拟,以植被盖度、降雨强度、坡度、土壤前期含水率和土壤容重5个因子作为输入层变量,次降雨下径流量作为输出层变量。利用野外人工模拟降雨试验所得到的不同降雨强度下各类土地经营径流小区的径流量实测资料,对网络进行模拟训练并预测,径流量平均误差不超过10%,且径流量较大的翻耕地训练精度及预测结果较草灌地、刈割准确性更高些。与传统回归统计方法进行了误差比较,结果表明,该模型能更好地预测次降雨的径流量。