降雨强度对农业耕作措施水土保持作用的影响

利用人工模拟降雨试验，研究不同降雨强度下，不同农业耕作措施坡地水土流失特征。试验设计的坡地坡度分别为5°和15°，降雨强度分别为60、90、120 mm·h^-1；耕作措施分别为等高耕作、人工掏挖和人工锄耕，以相同坡度的平整坡地作为对照。结果表明：（1）随着降雨强度的增大，各耕作措施坡地产流量显著增大1.51倍以上，最大增加幅度为等高耕作坡地的2.28倍。而坡地产沙量在降雨强度较小时增加不显著，当降雨强度增大到120 mm·h^-1时，坡地产沙量显著增大；（2）与平整坡地相比，等高耕作在3个降雨强度下都具有明显的减流效益，减流量均大于15%，而人工锄耕和人工掏挖却不明显；（3）在5°坡地上，等高耕作和人工掏挖在3个降雨强度的减沙效益均大于25%，而人工锄耕减沙效益不明显；在坡度为15°、降雨强度为60 mm·h^-1和90 mm·h^-1时，人工锄耕和人工掏挖减沙效益与降雨强度关系无明显规律，在降雨强度为120 mm·h^-1时，3个耕作措施都不能有效降低坡地产沙量。可见，水土保持农业耕作措施具有降低坡地产流量的作用，而对于坡地产沙的作用存在明显差异，在大坡度和大降雨强度下，不仅不能降低坡地产沙，反而加剧坡地土壤流失。     

Effects of structural and depositional crusts on soil erosion on the Loess Plateau of China

Conventional tillage practices used on the Loess Plateau lead to different soil surface micro-topography which results in forming two types of soil crusts. The objective of this study was to explore the formation position, properties and erosion characteristics of structural crusts and depositional crusts under the influences of the microtopography in the rainfall experiments. Two simulated rainstorms were applied in the experiments. The first rainfall event was used for soil crust formation, then the following simulated rainfall storms at 40 mm h^?1, 60 mm h^?1, and 80 mm h^?1 rates were applied to the soil boxes set to a 17.6% (10°) slope under three tillage types (contour tillage, artificial digging, and straight slope conditions) to investigate the resulting runoff discharge rate and sediment yield on crusted soil surface. Results show that: (1) structural crusts formed on the mounds, and depositional crusts formed in the depressions after the first rainfall events; structural crusts exhibit a lower thickness, bulk density, higher porosity and shear strength than depositional crusts; (2) structural crusts increased the runoff yield less and decreased the sediment yield more than depositional crusts; and (3) the runoff yield was significantly greater, and the sediment yield was lower on the crusted soil surface than that on the uncrusted soil surface, regardless of the effect of the tillage treatments.     

近60a黄河流域地表径流变化特征及其与气候变化的关系

利用气温、降水量和NCEP/NCAR地表径流资料,运用线性趋势系数、相关系数和不规则区域网格化方法,研究了近60a来黄河流域地表径流的变化及其与气候因素的相关关系。结果表明:1951-2010年整个黄河流域均为升温趋势,北部升温幅度高于南部;降水量正趋势主要位于黄河源区,中、下游地区为负趋势;地表径流变化在黄河源区(处于青藏高原)和河套北部(阴山南麓)呈现为增加趋势,其余广大的地区呈现为减少趋势;从不同年代的地表径流来看,不论是黄河源区还是广大的中、下游地区,上世纪60年代的径流量均是最高的,而二十一世纪10年代径流量是最低的;从整个流域来看,径流量与气温和降水均有较好的相关性。在黄河源区以外的流域内,降水与径流的关系好于气温,而在黄河源区则相反,不同区域差异的原因有待进一步研究。     

Bare Ground and Litter as Estimators of Runoff on Short- and Mixed-Grass Prairie

After 56 years of grazing on shortgrass prairie and 13 years of grazing on mixed-grass prairie, surface runoff was estimated with a rotating boom rainfall simulator. Runoff was strongly and positively correlated with percent bare ground, and was strongly and negatively correlated with percent litter cover. Neither foliar nor basal plant cover were useful estimators of runoff.     

聚丙烯酸钠对黄土坡面产流产沙的影响研究

通过野外模拟降雨试验,研究了施用SP对黄土坡面产流、产沙的影响,并对实验数据进行数学模拟,建立了SP施用量与产流、产沙强度间的关系模型.结果表明:SP施用量与产流时间、平均产流强度呈二次函数相关关系,与产沙强度呈线性负相关关系.SP用量在0～2.42 g/m\+2之间时,能够延缓坡面产流,用量为1.21 g/m\+2时延缓产流效果最明显;用量介于0～3.31 g/m2之间时,能够增加土壤入渗,减少坡面产流量,用量1.65 g/m2的增渗减流效果最佳;施用SP后,能够减少坡面输沙强度,且用量越大,减沙效果越明显.SP可影响坡面产流过程,用量1.8 g/m2时,能够减小产流初期径流强度增幅,用量为3.6 g/m2时,其产流过程线与对照极接近,而施用量增加到5.4 g/m2时,产流强度明显增大.SP对坡面产沙过程的影响表现为:随施用量增大,产沙强度峰值呈逐步减小的变化趋势.     

黄土区土质道路径流水动力学参数的灰色关联度分析

黄土区土质道路路面侵蚀是该地区土壤侵蚀中的重要形式之一,为了探讨其土壤剥蚀率与径流水动力学参数的相关关系,以便为该地区道路土壤侵蚀预报模型的建立提供帮助,采用室内人工降雨及放水冲刷实验、灰色关联度分析方法研究了裸露土质路和植草土质路的径流水动力学参数与土壤剥蚀率间的关系,结果表明:1)在15°坡度、不同雨强条件下,可根据径流量或水流功率计算土壤剥蚀率;2)在2mm.min-1雨强、不同坡度条件下,可根据水流功率或坡度计算土壤剥蚀率;3)在降雨加放水冲刷试验条件下,裸露土质路的土壤剥蚀率可通过径流水深或径流流速计算得出,而植草土质路的土壤剥蚀率可通过过水断面单位能量或径流量计算得出。因此,在无汇水条件时,根据径流水流功率计算土壤剥蚀率较为合理;在有汇水条件时,采用径流量计算土壤剥蚀率较为合理。     

石匣小区氮磷坡面流失特征研究

以石匣试验小区为研究对象,分析了小区特征对氮磷、泥沙流失的影响。结果表明:在不同的土地利用方式中果园产生的径流中氮磷浓度最高,林地最低,而氮磷的流失量标准小区最高,林地最低;免耕种植、梯田种植、鱼鳞坑造林等耕作方式会明显减少农田土壤的侵蚀及氮磷的流失,植被覆盖明显减少径流量和泥沙量,从而有效地控制农田氮磷污染物的流失;在其它条件相同的情况下,坡度小的小区氮磷流失量明显减小;降雨量与氮磷的流失量呈现明显的正相关;雨季径流中氮、磷主要以颗粒态存在,径流中的泥沙量与径流量有较好的线性关系(R=0.72)。     

薄土坡耕地石坎反坡水平阶水沙调控效果

为研究石坎反坡水平阶对于薄土坡耕地的水沙调控效果,设置了两个标准天然降雨径流小区（措施小区和对照小区）分别对次降雨径流和泥沙进行了观测,结果表明：石坎反坡水平阶措施能够有效地调控坡耕地地表径流,年均径流削减率为22.5%,且在短历时、大雨强降雨条件下的调控效果好于长历时、小雨强降雨;该措施对于坡耕地泥沙调控效果显著且稳定,年均泥沙削减率95.5%,措施小区的坡面产沙量随降雨特征值变化的波动幅度远远小于对照小区;石坎反坡水平阶措施通过减少坡面侵蚀,间接提高了坡耕地作物产量,春玉米年均增产6.2%。     

黄河中游小流域侵蚀产沙机理研究

本文研究的典型流域指基本上具有单一的下垫面物质组成的流域。本文选取黄河中游河段上的支流；皇甫川、窟野河、无定河上一些小流域作为典型流域进行分析研究。根据下垫面差异，将产沙区分为黄土区、基岩区、风沙区；通过各产沙因子对侵蚀产沙影响作用的分析，对三种产沙区进行定性到定量分析，全面研究了黄河中游产沙机理，并进一步提出了治理对策。     

Effects of plant residue management on soil properties,surface runoff,and soil loss under rainfall simulation in a semi-arid region in Iran

A 5-year field study was conducted on the effect of plant residue management on soil erosion, runoff, bulk density, penetration resistance, and organic carbon. There were three treatments: burning residues on field (BR), returning residues unto the soil surface after harvesting (TR), and removing residues from soil surface (RR) (control treatment). At the end of the 5-year treatment, a rainfall simulation at 90?mm?h^?1 was applied to each plot. After rainfall simulation started, the runoff volume and soil loss amount in samples were collected at four sampling times. The results showed that the runoff volume for BR (from 145.5?±?12.2 to 190.0?±?11.8?mL) differed significantly (p?≤?0.01) from that of RR (from 32.3?±?5.5 to 67.5?±?11.1?mL) and TR (from 10.0?±?0.7 to 16.7?±?3.3?mL). A significant difference (p?≤?0.01) was also observed between RR and TR regarding runoff volume and soil loss amount in different sampling times, except for the first sampling time (2–4?min). The runoff volume in BR and TR was 215% higher and 294% lower than that of the control (RR), respectively. As compared to the control (RR), soil loss decreased by 96.5% in TR but increased by 192% in BR. The BR increased soil bulk density and penetration resistance by 4.9% and 12.4%, whereas TR reduced them by 2.1% and 15.8%, respectively, as compared to the control (RR). The results indicated that the highest (0.35) and lowest (0.03) runoff coefficients were obtained for BR and TR treatments, respectively. It is concluded that returning plant residues to soil is the best residue management practice in decreasing soil runoff volume and controlling soil erosion in semi-arid regions.     

黄土坡面侵蚀方式演变过程中汇水坡长的侵蚀产沙作用分析

利用由位于坡面上部的供水装置和坡面下部的试验土槽组成的试验装置系统,通过模拟降雨试验,研究了不同降雨强度(50、75和100 mm/h)和不同坡度(15°、20°和25°)条件下坡面侵蚀方式演变过程中汇水坡长对侵蚀产沙的作用.结果表明,黄土坡面片蚀-细沟侵蚀-切沟侵蚀方式演变过程中汇水坡长对侵蚀产沙具有重要作用,且受降雨强度、坡度和侵蚀方式演变过程的综合影响.汇水坡长增加,使坡面片蚀-细沟侵蚀-切沟侵蚀发育速度明显加快,侵蚀产沙量明显增加.在坡面侵蚀不同发育阶段,汇水坡长对坡面侵蚀的产沙作用也不尽相同.当坡面以切沟侵蚀为主时,汇水坡长对坡面侵蚀产沙的作用最大,其次是以细沟侵蚀为主时.而以坡面片蚀为主时,汇水坡长对坡面侵蚀产沙的作用最小.通过对坡面侵蚀产沙量与汇水坡长的相关分析表明,它们呈正线性关系.     

Effects of vegetation near-soil-surface factors on runoff and sediment reduction in typical grasslands on the Loess Plateau,China

Vegetation near-soil-surface factors can protect topsoil from erosion,however,their contributions to the reduction of soil erosion,especially under natural rainfall events,have not been systematically recognized.This study was performed to quantify the effects of near-soil-surface factors on runoff and sediment under natural rainfall events on grasslands dominated by Bothriochloa ischaemum(Linn.)Keng(BI grassland)and Artemisia gmelinii Thunb.(AG grassland)in two typical watersheds on the Loess Plateau,China in 2018.By successive removal of the plant canopy,litter,biological soil crusts(BSCs)and plant roots,we established five treatments including plant roots,plant roots+BSCs,plant roots+BSCs+litter,intact grassland and bare land in each grassland type.In total,twenty runoff plots(5 m×3 m)with similar slopes and aspects were constructed in the two types of grasslands.Results showed that plant canopy,litter and roots reduced runoff,while BSCs,which swelled in the presence of water,increased runoff.In contrast,all of these factors reduced sediment yield.In addition,the reductions in runoff and sediment yield increased with I30(maximum 30-min rainfall intensity)for each vegetation near-soil-surface factor except for BSCs.Among these factors,plant canopy had the largest contribution to runoff reduction,accounting for 48.8% and 39.9% in the BI and AG grasslands,respectively.The contributions of these vegetation near-soil-surface factors to sediment yield reduction were similar(21.3%-29.9%)in the two types of grasslands except for BSCs in the AG grassland(10.3%).The total reduction in runoff in the BI grassland(70.8%)was greater than that in the AG grassland(53.1%),while the reduction in sediment yield was almost the same in both grasslands(97.4%and 96.7%).In conclusion,according to the effects of different vegetation near-soil-surface factors on runoff and sediment production,our results may provide more complete insight and scientific basis into the effects of various vegetation related factors in controlling soil erosion.     

Soil surface roughness change and its effect on runoff and erosion on the Loess Plateau of China

As an important parameter in the soil erosion model, soil surface roughness（SSR） is used to quantitatively describe the micro-relief on agricultural land. SSR has been extensively studied both experimentally and theoretically; however, no studies have focused on understanding SSR on the Loess Plateau of China. This study investigated changes in SSR for three different tillage practices on the Loess Plateau of China and the effects of SSR on runoff and erosion yield during simulated rainfall. The tillage practices used were zero tillage（ZT）, shallow hoeing（SH） and contour ploughing（CP）. Two rainfall intensities were applied, and three stages of water erosion processes（splash erosion（I）, sheet erosion（II） and rill erosion（III）） were analyzed for each rainfall intensity. The chain method was used to measure changes in SSR both initially and after each stage of rainfall. A splash board was used to measure the splash erosion at stage I. Runoff and sediment data were collected continuously at 2-min intervals during rainfall erosion stages II and III. We found that SSR of the tilled surfaces ranged from 1.0% to 21.9% under the three tillage practices, and the order of the initial SSR for the three treatments was ZT〈SH〈CP. For the ZT treatment, SSR increased slightly from stage I to III, whereas for the SH and CP treatments, SSR decreased by 44.5% and 61.5% after the three water erosion stages, respectively, and the greatest reduction in SSR occurred in stage I. Regression analysis showed that the changes in SSR with increasing cumulative rainfall could be described by a power function（R2〉0.49） for the ZT, SH and CP treatments. The runoff initiation time was longer in the SH and CP treatments than in the ZT treatment. There were no significant differences in the total runoff yields among the ZT, SH and CP treatments. Sediment loss was significantly smaller（P〈0.05） in the SH and CP treatments than in the ZT treatment.     

Freeze-thaw effects on erosion process in loess slope under simulated rainfall

Seasonal freeze-thaw processes have led to severe soil erosion in the middle and high latitudes. The area affected by freeze-thaw erosion in China exceeds 13% of the national territory. So understanding the effect of freeze-thaw on erosion process is of great significance for soil and water conservation as well as for ecological engineering. In this study, we designed simulated rainfall experiments to investigate soil erosion processes under two soil conditions, unfrozen slope (UFS) and frozen slope (FS), and three rainfall intensities of 0.6, 0.9 and 1.2 mm/min. The results showed that the initial runoff time of FS occurred much earlier than that of the UFS. Under the same rainfall intensity, the runoff of FS is 1.17-1.26 times that of UFS; and the sediment yield of FS is 6.48-10.49 times that of UFS. With increasing rainfall time, rills were produced on the slope. After the appearance of the rills, the sediment yield on the FS accounts for 74%-86% of the total sediment yield. Rill erosion was the main reason for the increase in soil erosion rate on FS, and the reduction in water percolation resulting from frozen layers was one of the important factors leading to the advancement of rills on slope. A linear relationship existed between the cumulative runoff and the sediment yield of UFS and FS (R²>0.97, P<0.01). The average mean weight diameter (MWD) on the slope erosion particles was as follows: UFS0.9 (73.84 μm)>FS0.6 (72.30 μm)>UFS1.2 (72.23 μm)>substrate (71.23 μm)>FS1.2 (71.06 μm)>FS0.9 (70.72 μm). During the early stage of the rainfall, the MWD of the FS was relatively large. However, during the middle to late rainfall, the particle composition gradually approached that of the soil substrate. Under different rainfall intensities, the mean soil erodibility (MK) of the FS was 7.22 times that of the UFS. The ratio of the mean regression coefficient C₂ (MC₂) between FS and UFS was roughly correspondent with MK. Therefore, the parameter C₂ can be used to evaluate soil erodibility after the appearance of the rills. This article explored the influence mechanism of freeze-thaw effects on loess soil erosion and provided a theoretical basis for further studies on soil erosion in the loess hilly regions.     

Effects of weed harrowing and undersown clover on weed growth and spring cereal yield

Weed competition and nutrient scarcity often restrict organic cereal production, especially where the availability of livestock manure is limited. While harrowing of annual weeds and legume cover crops can be used, these methods are both executed in early spring and may hinder each other. Two cycles of a 2‐year crop rotation were carried out in south‐east Norway (60°42′N, 10°51′E, altitude 250 m) with weed harrowing and undersown cover crops (WHCC) at two fertiliser rates (40 and 100 kg nitrogen ha^?1). The effect of the WHCC treatments was measured by weed density and species, weed biomass, changes in weed seedbank and grain yield. The weed density depended on the interaction between WHCC, fertiliser and year. On average, pre‐emergence weed harrowing reduced weed density by 32% and weed biomass by 49%, while pre‐ and post‐emergence weed harrowing reduced weed density by 59% and weed biomass by 67% compared with the untreated control. Spergula arvensis became more abundant at low rather than at high fertiliser rates. On average, white clover cover crop sown after pre‐emergence weed harrowing resulted in the highest yields for both oat (+12.1%) and wheat (+16.4%) compared with the untreated control. Despite differences in weed population density and biomass among WHCC treatments within years, the weed biomass, weed density and seedbank increased for all WHCC treatments over the 4‐year period. More research is required into improving the efficacy of mechanical and cultural weed suppression methods that organic systems rely on.     

Effects of freeze-thaw on soil erosion processes and sediment selectivity under simulated rainfall

The freeze-thaw(FT) processes affect an area of 46.3% in China. It is essential for soil and water conservation and ecological construction to elucidate the mechanisms of the FT processes and its associated soil erosion processes. In this research, we designed the control simulation experiments to promote the understanding of FT-water combined erosion processes. The results showed that the runoff of freeze-thaw slope(FTS) decreased by 8% compared to the control slope(CS), and the total sediment yield of the FTS was 1.10 times that of the CS. The sediment yield rate from the FTS was significantly greater than that from the CS after 9 min of runoff(P0.01). Both in FTS and CS treatments, the relationships between cumulative runoff and sediment yield can be fitted well with power functions(R20.98, P0.01). Significant differences in the mean weight diameter(MWD) values of particles were observed for washed particles and splashed particles between the CS and the FTS treatments in the erosion process(P0.05). The mean MWD values under CS were smaller than those under FTS for both washed and splashed particles. The ratio of the absolute value of a regression coefficient between the CS and the FTS was 1.15, being roughly correspondent with the ratio of K between the two treatments. Therefore, the parameter a of the power function between cumulative runoff and sediment yield could be an acceptable indicator for expressing the soil erodibility. In conclusion, the FTS exhibited an increase in soil erosion compared to the CS.     

冷荒漠草本植物数量特征对不同水分输入和气象因子的响应

草本层是古尔班通古特沙漠植被的重要组成部分，在维持沙漠稳定、养分循环等方面具有重要意义。水分通常以积雪和降雨形式输入到土壤，输入方式及数量变化对荒漠植物的存活和生长有重要影响。本文以古尔班通古特沙漠南缘草本层为研究对象，利用人工增减积雪的方法，共设置4个积雪处理(0，50%，100%，200%积雪，其中100%积雪为对照)，于2009—2016年春季调查草本植物的数量特征和物种丰富度，分析草本植物数量特征对水分变化的响应；同时结合气象数据，分析不同年份一年生荒漠草本植物数量特征与主要气象因子的关系。结果表明：表层土壤含水量与积雪厚度成正比，相应的草本植物的幼苗密度与积雪水当量、表层土壤含水量成正比关系；2009—2016年，年内积雪量的变化对物种丰富度没有显著影响，各积雪处理间物种丰富度差异不显著；2009—2016年自然处理下年际间物种丰富度差异显著，2015年物种丰富度显著小于其余年份。结合气象数据分析发现，物种丰富度年际变化主要受幼苗建成期的降雨调控，并且干旱年份过后的湿润年份物种丰富度不受前一年降水的影响，说明荒漠草本植物层片具有较强的自我调节能力；自然处理下，不同年份草本植物旺盛期的存活数量与大气干旱程度(空气饱和差)呈显著负相关关系（R²值为0.611，P<0.05），与生长季的降雨量呈正相关关系（R²值为0.162, P>0.05），说明大气干旱程度更能表征荒漠草本植物生长峰值期的存活情况。     

Impacts of land disturbance and restoration on runoff production and sediment yield in the Chinese Loess Plateau

Land disturbance and land restoration are important factors influencing runoff production and sediment yield in the semi-arid loess regions of China. This study compared the runoff production and sediment yield during the early stage after land disturbance(ESLD) with those during restoring stage after land disturbance(RSLD). Grey relational analysis was used to analyse the importance of each one of the influencing factors(vegetation, rainfall, soil and topography) in affecting the runoff production and sediment yield. Our results showed that during ESLD, topography was the most critical factor controlling the runoff production, while soil was the most important factor controlling the sediment yield. During RSLD, vegetation was more important in affecting runoff production, while rainfall was more important in affecting sediment yield. In additional, this study demonstrated that both the runoff production and the sediment yield can be effectively reduced by restoring vegetation on severely-disturbed lands, thus providing an important theoretical basis for better implementations of the Grain for Green Program. Our results revealed that the vegetation types of Hippophae rhamnoides+Pinus tabulaeformis and H. rhamnoides are better plant selections for land restoration in this area, especially for relatively gentle slopes(i.e., less than 20 degrees).     

雨强和植被覆盖度对典型坡面产流产沙的影响

应用先进的UGT水蚀测量仪,研究黄土高原祖厉河流域雨强和植被覆盖度对典型坡面产流产沙的影响。结果表明:黄土高原半干旱区间隔为15min的产流量、径流含沙量和产沙量与15min雨强具有相同的增减趋势,呈三次曲线关系y=b0+b1x+b2x2+b3x3。7种雨强条件下,人类扰动撂荒地的产流量、径流含沙量和产沙量均明显大于植被自然恢复的撂荒地,覆盖度20%的撂荒地是覆盖度35%撂荒地的平均径流系数的2.35倍,径流含沙量的4.48倍,产沙量的14.06倍。相对于受到扰动的撂荒地,植被自然恢复的撂荒地水土保持效益显著。     

Seeding and Mulching Treatments as Conservation Measures of Two Burned Soils in the Central Ebro Valley,NE Spain

The effectiveness of seeding introduced species, with or without straw mulching, was tested as a measure of post-fire erosion control in gypsiferous (Xeric Haplogypsid) and calcareous soils (Xeric Torriorthent) in Central Ebro Valley (NE-Spain). Paired control, seeding, and combined seeding and mulching plots were established in four replicated plots for each soil tested. Seeding rate was 30 g m -2 and straw mulch was applied at 100 g m -2 in each plot. Plant projective cover (total and specific), plant biomass, bare soil cover and sediment yield were determined over a 2-year period. During the first year of sampling, species introduced by seeding increased plant cover (about 30%) without significant differences observed between soils. Plant cover was similar in seeding-only and seeding-mulching treatments, although the latter treatment significantly enhanced plant weight. During the second year these differences disappeared because species introduced by seeding practically did not survive. So, the introduced herbs did not interfere with native plants. Bare soil cover remained significantly lower in treated plots than on the control plots for both soils during both years of sampling. In the second year, the reduction of bare soil was attributed to both the straw mulch and litter from the seeding species. Soil protection was significantly higher in calcareous soils than in gypsiferous soils which is related to their physical and chemical properties. Cumulative sediment yield decreased significantly over time with both treatments on both soils. Soil losses from control plots were three times higher than seeding plots and 3.3 times higher than from seeding and mulching plots in gypsiferous soils. Soil losses from control plots were two times higher than from seeding plots and 2.7 times higher than the combined seeding and mulching plots in the calcareous soils. Cumulative soil loss was higher from the gypsiferous soils than from the calcareous soils due to the lower plant cover.