不同砾石盖度戈壁床面动力学特征研究

利用野外车载移动式风洞,对莫高窟顶不同砾石盖度戈壁床面的动力学特征进行了实地模拟实验。结果表明：砾石盖度直接决定戈壁床面的粗糙元数量和分布状况,进而影响近地表风速廓线、摩阻速度、床面粗糙度和剪切力;随着风洞进口指示风速的增加,摩阻速度呈线性递增,而动力学粗糙度在波动中呈下降趋势;相同高度,随着砾石盖度的增加,近地表风速逐渐降低,而摩阻速度、动力学粗糙度和剪切力呈线性增加;当床面盖度增加至35%时,动力学粗糙度达到0.30 cm,摩阻速度相应提高到0.93 cm/s,床面剪切力增加至1.11 N/cm。     

草原灌木带空气动力学粗糙度研究

为了定量研究灌木带修复退化草原的机理,采用集沙仪和风速廓线仪野外采集了不同高度灌木带及退化草原的风蚀物及风速廓线,利用最小二乘法对风速廓线数据进行计算得到了相应的空气动力学粗糙度。结果表明:灌木带对草地的防护机理在于提升了地表的空气动力学粗糙度,降低了近地表的风速,从而导致灌木带相对退化草原的抗风蚀能力增强,大量风蚀物集中在近地表30 cm范围内;距灌木带的距离越远,空气动力学粗糙度呈现下降趋势;同时对不同高度灌木带的研究发现,0.3 m、0.7 m和1.5 m高的灌木带分别在距背风面3 m、5 m和6 m处的空气动力学粗糙度与退化草原的值趋于一致,此距离为该灌木带的有效防风蚀范围,空气动力学粗糙度及有效防护范围均随灌木高度的增加而增大。     

河北坝上不同土地利用方式对土壤风蚀的影响

对河北坝上康保地区天然草地、人工林、农田和退耕地四种土地利用方式的输沙量、风速廓线以及土壤的理化性质进行观测和分析。结果显示:天然草地的地表硬度最大,输沙量最小,表层土壤粗颗粒含量最低;农田地表含水量和硬度最小,输沙量最大,有机质含量最低,表层土壤粗颗粒含量最高;人工林地土壤水分含量较高,输沙量较低,有机质含量较高;退耕还灌木地表层含水量较低,地表硬度和空气动力学粗糙度较大,输沙量大于林地,有机质含量低于林地。表明土壤风蚀受地表含水量、硬度以及空气动力学粗糙度的共同作用影响,三者均不同程度受地表植被的影响,反映了地表植被类型对土壤风蚀的潜在影响。因此,在优先保护原生植被的前提下,重视植被生态恢复建设,着重提高地表植被覆盖度,以改善土壤结构,提高土壤有机质含量,增强土壤抗风蚀能力。     

作物残茬覆盖对农田土壤风蚀的影响

为定量评价干旱半干旱地区农田土壤抗风蚀效果,采用移动式风洞及其配套测试系统对内蒙古武川县上秃亥乡农田地表进行了原位测试研究。结果表明,不同风速下土壤风蚀量随作物残茬盖度的增加呈指数规律减少;40%以上残茬盖度可明显提高土壤颗粒起动风速并减少风蚀量;当风速为14~18 m/s时,地表作物残茬盖度为60%~80%具有较好的抗风蚀效果。     

空气动力学地表粗糙度样本容量的研究

借助风速数据自动采集系统获取的资料,计算了冀西北半干旱风沙生态类型区9种下垫面的空气动力学地表粗糙度,并从统计学角度分析了其变异特性和在一定精度要求下粗糙度与样本容量估计值的关系。结果表明:不同下垫面粗糙度差异显著,这与作物残茬、耕作类型等密切相关;地表粗糙度愈小,变异系数愈高,在同一给定相对精度下样本容量估计值越大,粗糙度与样本容量呈对数型负相关;同一下垫面相对精度要求越高,样本容量估计值越大。在划分粗糙度等级并给出相应的相对精度基础上,提出兼顾操作性与监测精度要求的样本容量估计值为100组。     

西北风蚀区种植甘草对地表微环境和土壤物理性状的影响

实验以风蚀区甘草植被为研究对象,采用空间序列代替时间序列的研究方法,对不同生长年限甘草地的地表微环境和土壤物理性状进行了研究。结果表明:甘草植被的盖度、植株高度和地上生物量随生长年限的增加而增加;与裸地相比,甘草植被的地表粗糙度提高12-55倍,表层土壤(0-5cm)含水率增加27%-148%,而土壤容重和粒径分别降低0.7%-19.4%和33.1%-48.8%。种植甘草不仅能使地表粗糙度、湿度、土壤含水率和孔隙度随甘草地上生物量(或生长年限)的增加而提高,而且还能使表层土壤的容重和平均粒径随甘草地上生物量的增加呈减小趋势;西北风蚀区若能在沙化耕地中推广种植甘草,不仅能改善当地生态环境,而且还能提高耕地经济效益。     

中国北方农牧交错区夏季土壤风蚀研究——以河北丰宁县大滩乡二道河为例

土壤风蚀与风速、土壤粒径组成和地表的植被盖度有关 ,在农牧交错区 ,夏季存在着风蚀风速 ,由于植被盖度的增大 ,减缓了夏季风蚀现象的发生。所以 ,降低放牧强度 ,保持一定的植被盖度 ,不但能阻止夏季风蚀现象的发生 ,而且对来年春季的生态状况有较大影响。     

不同盖度沙蒿群丛防风作用研究

以天然沙蒿群丛为研究对象,初始盖度为60%,人工降低其盖度为50%,40%和30%,用多剖面自计式遥测风速仪连续观测记录沙蒿林内距离地面0.1 m,0.5 m,1.0 m,2.0 m,3.0 m,4.0 m,5.0 m和6.0 m高度处的风速变化。当沙蒿群丛盖度由30%增加到60%,风速廓线变化不明显,风速廓线方程、空气动力学粗糙度、边界层位移厚度和边界层动量损失厚度的值较为接近,没有随盖度呈现出规律性的变化,在这个盖度变化范围内,沙蒿群丛降低风速的作用相似。     

策勒不同下垫面风速廓线时空差异研究

通过对新疆策勒4个下垫面10m高风速廓线及粗糙度、摩阻风速等分析,探讨不同时空条件下植被和地形对风场的影响。结果表明:在中性层结下,从流沙前沿到半固定沙地、固定沙地扬沙天气风速廓线斜率依次降低,风速较大时基本符合对数关系,其拟合程度依次是半固定沙地﹥固定沙地﹥流沙地,绿洲内部2m以上高度的风速较大时与高度基本符合对数关系。春季沙尘暴期间风速较小时半固定沙地0-10m高及绿洲内部2m以上高度风速与高度变化接近对数关系,当夏季沙尘暴风速较大时,4个下垫面不同高度风速与高度之间都不呈现对数关系。随着地表植被覆盖度的增加,粗糙度和摩阻风速也迅速增加,绿洲内部夏季沙尘暴天气近地表粗糙度比春季地表粗糙度增加较为显著。     

绿洲农田防护林系统土壤蒸发特征研究

以景电灌区绿洲农田防护林系统为研究对象,通过对农田防护林系统内土壤水分蒸发的测定分析,结果表明:在1H范围内,越靠近林带,土壤蒸发量越大。随着与林带距离的增加,土壤蒸发量有先减小后增大的趋势;农田防护林系统内土壤水分蒸发量在灌溉前后有先增加后减小的趋势,并且对照点土壤水分蒸发量始终高于林网内观测点,林网内土壤蒸发量与对照点相比平均减少了35.17%。说明绿洲农田防护林系统能有效减弱土壤蒸发量;相关分析表明,系统内土壤水分蒸发量受到土壤本身和气象因子的制约,其影响程度大小依次为土壤含水量>太阳辐射>空气相对湿度>风速>气温,其中土壤含水量、太阳辐射、气温、风速与土壤蒸发量成正相关,空气相对湿度与其成负相关关系。     

Impact factors of soil wind erosion in the center of Taklimakan Desert

The development and progress of soil wind erosion are influenced by the factors of climate,terrain,soil and vegetation,etc. This paper,taking Tazhong region,a town in the centre of the Taklimakan Desert,as an example and using comparative and quantitative methods,discussed the effects of climate,surface roughness(including vegetation cover) and surface soil properties on soil wind erosion. The results showed that the climate factor index C of annual wind erosion is 28.3,while the maximum of C is 13.9 in summer and it is only 0.7 in winter. The value of C has a very good exponential relationship with the wind speed. In Tazhong region,the surface roughness height is relatively small with a mean of 6.32 × 10-5 m,which is in favor of soil wind erosion. The wind erosion is further enhanced by its sandy soil types,soil particle size,lacking of vegetation and low soil moisture content. The present situation of soil wind erosion is the result of concurrent effects of climate,vegetation and surface soil properties.     

三种不同床面近地层湍流输送特征

为了深入理解土壤风蚀发生机制,利用风洞实验风速廓线资料,采用空气动力学方法,计算了干旱、半干旱地区不同类型地表近地层湍流输送随风速以及地表性质的变化特征.结果表明:地表越粗糙,风速越大,湍流输送越强,且湍流输送强度与地面粗糙元密度有关.     

灌木林优化配置格局对土壤风蚀的影响

低覆盖度时,灌木林的水平配置格局成为制约土壤风蚀的重要因素。以宁夏盐池县风沙区人工灌木林基地为试验区,研究了不同下垫面类型和不同配置格局的灌木沙障对风速、近地表输沙率和地表粗糙度的影响。结果表明:灌木林的防治土壤风蚀能力与灌木林的种类、高度和配置格局有直接关系:行带式配置能显著提高灌木林的防风效果,其中以沙柳林效果最佳;三行一带、平均高1.5m、行距1.5m、插深0.5m配置规格的沙柳沙障对地表土壤风蚀的控制效果最好,但防护范围限15倍带高以内;在行数一定的情况下,沙障高度越低,控制土壤风蚀能力越强。     

A field investigation of wind erosion in the farming–pastoral ecotone of northern China using a portable wind tunnel: a case study in Yanchi County

The farming–pastoral ecotone in northern China is an extremely fragile ecological zone where wind erosion of cropland and rangeland is easy to occur. In this study, using a portable wind tunnel as a wind simulator, we conducted field simulated wind erosion experiments combined with laboratory analysis to investigate wind erosion of soils in trampled rangeland, non-tilled cropland and tilled cropland in Yanchi County, China. The results showed that compared with rangeland, the cropland had a higher soil water holding capacity and lower soil bulk density. The wind erosion rate of trampled rangeland was much higher than those of non-tilled cropland and tilled cropland. For cropland, the wind erosion rate of the soil after tilling was surprisingly less than that of the soil before tilling. With increasing of wind speed, the volume mean diameter of the eroded sediment collected by the trough in the wind tunnel generally increased while the clay and silt content decreased for all soils. The temporal variation in wind erosion of the trampled rangeland indicated that particle entrainment and dust emission decreased exponentially with erosion time through the successive wind erosion events due to the exhaustion of erodible particles.     

An experimental study on the influences of water erosion on wind erosion in arid and semi-arid regions

Complex erosion by wind and water causes serious harm in arid and semi-arid regions. The interaction mechanisms between water erosion and wind erosion is the key to further our understanding of the complex erosion. Therefore, in-depth understandings of the influences of water erosion on wind erosion is needed. This research used a wind tunnel and two rainfall simulators to investigate the influences of water erosion on succeeding wind erosion. The wind erosion measurements before and after water erosion were run on semi-fixed aeolian sandy soil configured with three slopes(5°, 10° and 15°), six wind speeds(0, 9, 11, 13, 15 and 20 m/s), and five rainfall intensities(0, 30, 45, 60 and 75 mm/h). Results showed that water erosion generally restrained the succeeding wind erosion. At a same slope, the restraining effects decreased as rainfall intensity increased, which decreased from 70.63% to 50.20% with rainfall intensity increased from 30 to 75 mm/h. Rills shaped by water erosion could weaken the restraining effects at wind speed exceeding 15 m/s mainly by cutting through the fine grain layer, exposing the sand layer prone to wind erosion to airflow. In addition, the restraining effects varied greatly among different soil types. The restraining effects of rainfall on the succeeding wind erosion depend on the formation of a coarsening layer with a crust and a compact fine grain layer after rainfall. The findings can deepen the understanding of the complex erosion and provide scientific basis for regional soil and water conservation in arid and semi-arid regions.     

土壤风蚀量随残茬高度的变化规律研究

在内蒙古自治区武川县建立农田土壤风蚀试验区,采用内蒙古农业大学研制的移动式风蚀风洞和旋风分离式集沙仪,直接在农田上观测不同残茬高度条件下的农田风蚀土壤损失情况。试验结果表明:土壤风蚀量和扬起沙尘的高度随风速的增加而增加,随着作物秸秆残茬高度的增加而降低,且输沙量与高度变化符合指数函数关系,土壤颗粒主要集中在近地表层内运动。保护性耕作可明显地提高启沙风速,减少农田土壤损失,当秸秆高度为30 cm时,风蚀量仅为传统耕地的1/4左右。     

残茬高度对土壤风蚀量影响的试验研究

在内蒙古自治区武川县建立农田土壤风蚀试验区,采用内蒙古农业大学研制的移动式风蚀风洞和旋风分离式集沙仪,观测不同残茬高度条件下农田土壤的风蚀情况.试验结果表明:土壤风蚀量和扬起沙尘的高度随风速的增加而增加,随着作物秸秆残茬高度的增加而降低,且风蚀量与高度变化符合指数函数关系,土壤颗粒主要集中在近地表层内运动.保护性耕作可明显地提高起沙风速,减少农田土壤损失,当秸秆高度为30 cm时,风蚀量仅为传统耕地的1/4左右.     

Effect of different weed management systems on the weed populations, and seedbank composition and distribution in tropical coconut plantations

Weeds are a perennial problem in coconut plantations and cause significant losses in the nut yield. The occurrence of a wide range of weeds also causes difficulties in their eradication. The influence of five different weed management practises on the distribution and composition of the soil weed seed bank in coconut plantations in the low-country dry zone of Sri Lanka was evaluated. The treatments imposed included the application of glyphosate (N-[phosphonomethyl]-glycine), cover cropping with Pueraria phaseoloides , tractor harrowing, tractor slashing, and tractor plowing. All the treatments were applied twice per year, except for the cover cropping treatment. In terms of a reduction in the weed biomass, the application of glyphosate and cover cropping ( Pueraria ) were more efficient in reducing the ground weed population. These methods were very effective in reducing the weed seed density in the top soil layers. Plowing and harrowing significantly reduced the seed bank in the top soil layers and shifted significant numbers of weed seeds to deeper soil profiles. However, the total germinated weed seed count increased by 123.5, 691.4, 1133.1, and 1216.5% in the 10–15, 15–20, 20–25, and 25–30 cm soil depths, respectively, compared with the initial germinated weed seed count in the plowing treatment. Considering all the soil layers, the decline in the germinating weed seed count was very high in the treatment plots with cover cropping and the application of glyphosate; thus, these are considered to be the best practises to reduce the germinating weed seed count in the soil of coconut plantations.