土壤风蚀是我国北方沙漠化土地扩展和沙尘灾害频繁爆发的根源。风蚀强度决定于近地表气流侵蚀力和土壤可蚀性两个方面。土壤风蚀的防治应从人为能够改变的因素出发，降低侵蚀力，增强表层土壤的抗蚀性，达到降低风蚀强度的效果。北方农牧交错区的旱作农田和退化草地是沙漠化扩展和沙尘释放的主要地表类型。作物留茬和垄作是农田休闲期防风抗蚀的保护性耕作措施，草地的风蚀强度则决定于植被类型、高度和盖度等参数。定量分析两种地表上气流侵蚀力和输沙率随植被、土垄、土块粗糙元特征的变化规律，可揭示各粗糙元防风抗蚀的机制，为确定防治风蚀所需的粗糙元标准提供参考。此外，区域气候侵蚀力年内变化和输沙方向的分析可为适时而合理的实施风蚀防治措施提供依据。通过统计内蒙古太仆寺旗2000年风速数据，对我国北方典型农牧交错区年内风沙活动期、起沙风频率、输沙势和输沙方向进行分析。观测农田留茬、垄作、土块覆盖和草地地表0-4 m内不同高度的风速，分析留茬、草被、土垄、土块等粗糙元改变近地表气流场，降低风速的幅度，揭示其防治风蚀的机制，确定了莜麦留茬、油菜留茬、小麦留茬及草被的有效防风高度。通过室内风洞模拟和野外风沙观测，观测不同结构的垄作和不同耕作强度下风蚀速率、风沙流结构，分析两者随垄作结构和地表土块覆盖度的变化规律。结果表明：研究区气候干燥，降水稀少，年蒸发量是降水量的4.5倍。年起沙风频率和输沙势分别为20 %和284.8个矢量单位，合成输沙方向为S65.5ºE，方向变率为0.87，年风况属单向中能型。风沙活动期3月至5月内，该地区起沙风频率和输沙势达36 %和155个矢量单位，属锐双峰高风能环境，输沙方向与年输沙方向基本一致。该地区经济落后，农业缺乏灌溉，以粗放的旱地种植业为主，农作物产量与降水量密切相关。农田休闲期作物留茬的面积比例不足15 %，传统翻耕后表层土壤裸露疏松，易遭受侵蚀。此外，近年来牲畜头数增多，草原承受压力加大，加上樵采药材和车辆碾压的人为干扰，草地退化严重。作物留茬和草被是降低休闲期农田和退化草地的近地表风速，抵御土壤侵蚀的主要植被粗糙元。传统翻耕、浅耕、翻耕覆盖、深松、油菜高低茬、小麦高低茬及冰草地等9种下垫面的近地表风速观测显示，植被对风速的降低幅度随观测高度的增大而降低，各种地表间风速的差异在地上1 m高度以内较为明显。0.05 m高度的相对风速比较，传统翻耕、浅耕、翻耕覆盖和深松地表在0.4左右；油菜低茬下稍低于0.4；油菜高茬和小麦低茬相近，为0.25；小麦高茬最小，在0.2以下；易倒伏的冰草地表则与浅耕等翻耕措施相当。各处理下空气动力学粗糙度、摩阻速度和风速的相对脉动强度比较结果与相对风速的差异基本一致，近地面相对风速越大，以上三个空气动力学参数越小，地表植被粗糙元对气流的摩擦阻力越弱。可见，留茬比其它耕作措施和冰草覆盖降低风速的效果更为明显，而风速降低幅度随留茬高度和密度的增加而增大，密度较大的小麦茬比稀疏油菜茬的防风效果更好。而不同种类的留茬地表，风速降低的幅度和空气动力学参数随茬高的变化规律表明，莜麦、油菜和小麦留茬高度达到15、30、15 cm时，地上0.1 m高度风速显著降低，空气动力学粗糙度分别是茬高5 cm处理的2.5、3.3和3.5倍，残茬对气流的摩擦阻力明显增大，是各种留茬类型下降低风速的有效茬高。此外，不同草地类型的防风效益也存在较大差异。近地表风速、空气动力学粗糙度和摩阻速度比较显示，茎秆直立性较差的冰草、羊草和老芒麦覆盖下近地表风速较大，空气动力学粗糙度和摩阻速度较小，而茎秆直立性强的赖草、艾草、麻花头及大籽蒿草地则相反。同一草地的防风效果随植被高度和盖度的增大而增强，地表空气动力学粗糙度和摩阻速度均与草地植被高度存在正相关关系。作物秸秆和残茬在我国北方的农村常被用作饲料或燃料，垄作地表的土垄和翻耕地表的非可蚀性土块则是作物残茬和秸秆的有效替代。野外垄作下不同地表位置风速的同步观测和空气动力学分析表明，与垄作田上风地带比较，土垄间和下风向地带近地表0～1 m内风速明显降低，在水平方向上距离垄作田越近，风速的降低幅度越大，在垄间达到最大。地表空气动力学粗糙度、摩阻速度和0.05 m处风速的相对脉动强度，均自垄作地表的上风向至下风向先增大后减小，在垄间位置达到最大。可见，垄作降低风速，增大地表粗糙度和对气流的摩擦阻力是其降低侵蚀力，控制风蚀的机制。而垄作控制土壤风蚀的效率与垄高、垄沟比及垄顶距等结构参数密切相关。对垄高为15 cm、20 cm、25 cm，垄沟比为1/6、1/12和1/24的9种结构的垄作下风速观测表明，垄高15 cm，垄沟比为1/6、1/12及垄高25 cm，垄沟比为1/6的三种垄作下近地表风速降低幅度、地表空气动力学粗糙度和摩阻速度较大，非可蚀性土垄粗糙元对气流运动的摩擦阻力较强，是适宜防风的垄作方式。农田翻耕后地表的非可蚀性土块是另一种作物秸秆等植被粗糙元的有效替代。犁耕后农田地表上半径大于15 cm土块的盖度可达27.67 %，地表空气动力学粗糙度在1 cm以上。随后的耙磨、抹平则会破坏土块结构，尤其是抹平后土块盖度仅为2.13 %，地上0.1 m高度的风速增大10 %，空气动力学粗糙度降低至0.05 cm。因此，合理选择犁耕、耙磨和抹平作业的时间，使风季内地表保持土块覆盖状态，可有效降低风的侵蚀力。不同结构的垄作和平作的土壤风蚀风洞模拟显示，垄作较平作下风蚀速率降低20～40 %，尤其在风速大于15 m s-1的强风下效果更为显著。垄作间比较：垄脊高度相同时，垄沟比越大，土壤风蚀速率越小；垄沟比相同时，垄脊越高，土壤风蚀速率越大；风蚀速率与相邻土垄的间距成正相关关系。此外，垄作降低了近地表气流的输沙比例，削弱了风沙流对农田地表作物幼苗的危害。0～20 cm风沙流结构分析表明，垄作较平作减小了地表以上4 cm和10 cm内的输沙量百分比。垄作间比较：垄脊高度相同时，垄沟比越大，Q0-4 / Q0-20 和Q0-10 / Q0-20越大；垄沟比相同时，垄脊越高，Q0-4 / Q0-20 和Q0-10 / Q0-20越小。各种垄作中，以高3 cm，垄沟比为1/3的垄作降低风蚀速率和近地表输沙率的效果最优。而土块覆盖的翻耕地表与其耙磨抹平后的风蚀对比观测表明，耙磨抹平后土壤风蚀速率增大数十倍。随耙磨抹平后土壤可蚀性的增强，风沙流发育所需的饱和路径减小：翻耕后土块覆盖的田块内，距离上风向21 m处Q0-10/Q0-60仅为22.12 %，而耙磨抹平后距离上风向边界10 m处Q0-10/Q0-60的值已达到44.82 %。可见，结构适宜的垄作和翻耕后地表的土块结构可抑制风蚀和风沙流发展，是降低土壤风蚀速率，削弱风沙流危害的有效耕作措施。综上所述，我国北方农牧交错区土壤风蚀防治应在农田休闲期实施适宜高度的作物留茬或结构合理的垄作，保持草地地表的覆盖，降低气流侵蚀力，抑制沙尘起动。而风沙活动期（3月至5月）前，对裸露农田翻耕，使其表面保持土块覆盖，则是农田土壤风蚀防治的应急措施。

Wind erosion is the origin of extend of desertification land and frequently occur of sand disaster in northern China. And the intensity of wind erosion was determined on wind force and soil erodibility. Wind erosion control should start from modifying elements that can be changed by people, reduce wind force, strengthen resistance of surface soil to wind force, achieve the purpose of erosion rate reduction. Rainfed farmland and degraded grassland are the main origin surfaces of desertification and sand disaster in farming and pastoral zone of northern China. Crop stubble and ridge-tillage are two effective measures for wind erosion control, and the intensity of wind erosion on these land surfaces are determined by roughness elements as configuration, type, height, and coverage of vegetation or ridge-tillage. Quantity analysis of the change of wind force and sand transport rate with characteristic change of roughness elements as vegetation, ridge and clods on soil surface of rainfed farmland and grassland can reveal the mechanism of these roughness elements to control wind erosion, afford theoretic base for determining effective roughness elements criterion to control wind eroion. In addition, analysis of annual change of climate erosivity and direction of sand transport can afford reference for implement reasonable wind erosion control measures in time. Through calculating wind data of weather station in Taibus county of Inner Mogolia, aeolian period, frequency of threshold wind velocity, drift potential and sand transport direction were analyzed. And through wind velocity observation on field surfaces with crop stubble, ridge tillage, clods cover and grassland, change of airflow character and decreased extent of wind velocity near field surface, caused by crop stubble, grass, ridges and clods roughness, were analyzed. It reveals the mechanism of roughness elements to control wind erosion, and determined the effective height of stubble of naked oat, wheat, oilseed rape and grass for wind erosion control. Through wind tunnel simulation and blown-sand field observation, we discuss the vary law of wind erosion rate, blown-sand structure, and their changes with increasing field length under field surfaces with different configuration of ridge tillage and clods coverage. The research results indicate:The climate of study region is arid, with less precipitation, and the annual evaporation is four and half of rainfall. During earlier spring from March to May, wind force was strong, and sandy soil surface was arid and loosen, which make it easy suffered from wind erosion. And annual frequency of blown-sand wind and drift potential were 20 % and 284.8 vector unit, and the resulted direction of sand transport was S65.5ºE, and varied rate of wind direction was 0.87. According the category criteria of wind force energy, this region belongs to single direction and middle intensity wind force. During aeolian period, frequency of blown-sand wind and sand drift potential reach 36 % and 155 vector unit, and during March and April frequency of blown-sand wind reach 35.1 % and 49.2 % respectively, sand drift potential reach 43.9 and 85.4 vector unit. During this period, wind environment belongs to high wind energy with two climaxs appearring acute angle, and sand transport direction was same to the direction of annual sand transport. The economy of the region was undeveloped. Being no irrigation, agriculture production was mainly rainfed planting with seldom management. And crop yield has close relation to amount of precipitation. Under traditional cultivation, farmland surface were bared and loosen in fallow, which make it easy suffered from wind erosion. And with the increasing of livestock, digging of medicinal materials and suppress of vehicle, grassland degraded seriously. Thus, rainfed farmland and degraded grassland became the main type of soil surface for land desertification and dust release. Crop stubble and grass cover are the main vegetation roughness elements to decrease wind velocity near field surface and resist soil wind erosion. Results of wind velocity observation under nine kinds of field surface i.e. traditional tillage, shallow ploughing, stalk mulch after ploughing, subsoil tillage, no tillage with tall rape stubble of 45 cm high, no tillage with short rape stubble of 10 cm high, no tillage with tall wheat stubbles of 45 cm high, no till with short wheat stubbles of 10 cm high and Agropyron cristatum, indicate that, reduced extent of wind velocity caused by vegetation decreased with increasing height, and difference exist among wind velocities in the height of 0-1 m under various field surfaces. Comparison of relative wind velocities at 0.05 m height indicated, relative wind velocities at 0.05 m height under traditional tillage, shallow ploughling, stalk mulch after ploughing and subsoil tillage were about 0.4, while for short rape stubble less than 0.4, for short wheat stubble and tall rape stubble were 0.25, and for tall wheat stubble less than 0.2. And under easier bended Agropyron cristatum grassland, relative wind velocity was close to that under cultivation measures, such as shallow ploughing etc. Among various treatments, discrepancy of aerodynamic roughness, friction velocity and relative wind velocity have the same tendency, and friction force caused by vegetation decreased with increasing relative wind velocity and that three aerodynamic parameters. So effects of crop stubble for reducing wind velocity were better than that of ploughing tillage and Agropyron cristatum, and reduced extent increased with increasing height and density of crop stubble. Wind velocity near soil surface under wheat stubble with high density was lower than that under oilseed rape with low density, and aerodynamic roughness and friction velocity were bigger. Analysis results of the changes of wind velocitie's reduced extent and aerodynamic parameters with increasing height of crop stubble indicate, wind velocity at 0.1 m high decreased significantly when crop stubble height reach 15, 30, 15 cm for naked oat, oilseed rape and wheat respectively, and their aerodynamic roughness were more than 2.5, 3.3 and 3.5 times of that under 5 cm high stubble treatments. So these height were regarded as the effective heights to control wind erosion for these three kinds of crop stubble. For easier bended, Agropyron cristatum reach it effective point controlling wind erosion at 22 cm high and 75 % coverage. In addition, efficiency of grass for controlling wind erosion varied with the grass type, these grass with strong stalk, such as Leymus secalinus, Aremisia argyi, Serratula centauroides and Artemisia sieversiana, have much better benefits than these grass with soft stalk, such as Agropyron cristatum, Aneurolepidium chinense, in decreasing wind velocity and increasing aerodynamic roughness and friction velocity. For the same type of grass, decreasing extent of wind velocity increased with increasing height and coverage of vegetation, and aerodynamic roughness and friction velocity have positive relation with grass height. Stalk and stubble often are used as feed or fuel in farming and pastoral zone of northern China, while ridge tillage and nonerodible clods on ploughing soil surface can replace stalk and stubble effectively. Field observation of wind profiles and analysis of aerodynamic parameters at different locations synchronously on field surface with ridge tillage, including locations at windward area, between ridge, at leeward area, indicated time-average velocities of 0~1 m in ridge-tillage or at leeward area were obviously lower than that at windward area. In horizontal direction, the decreased percentage of wind velocity, aerodynamic roughness, friction velocity and relative fluctuation intensity of wind velocity at the height of 0.05 m were all decreased with the increasing distance between the observation point and ridge-tillage. And all the four parameters within ridge-tillage were the biggest. Decreased wind velocity and increased aerodynamic parameters mean friction force of ridge tillage to wind flow bigger than that under flat soil surface, which is its mechanism for wind erosion control. While efficiency of ridge tillage for decreasing wind velocity and increasing aerodynamic roughness have closely relation with configuration parameters of ridge tillage, such as ridge height (RH), ratio between ridge height and furrow width (RBRF), spacing between adjacent ridges (SBAR). Compared observation of wind velocity among nine kinds of ridge tillage with ridge height 15 cm, 20 cm, 25 cm, and ratio between ridge height and furrow width 1/6, 1/12 and 1/24 indicate that three kind of ridge tillage, i.e. 15 cm height, 1/6 and 1/12 ratio between ridge height and furrow width, 25 cm height, 1/6 ratio between ridge height and furrow width, appeared better benefits on decreasing wind velocity at 0.05 m high above soil surface, also on increasing aerodynamic roughness, friction velocity and friction force to wind flow, which make them suitable configuration of ridge tillage for wind erosion control. In addition, nonerodible clods coverage also is an effective replace of crop stubble except ridge tillage. Coverage of clods with semidiameter larger than 15 cm reach 27.67 % on soil surface after ploughing, and aerodynamic roughness above 1 cm high. While following harrowing and milling destroyed clods structure. Especially after milling, coverage of clods was only 2.13 %, wind velocity at 0.1 m high increased 10 %, and aerodynamic roughness decreased to 0.05 cm. So choosing reasonable time to perform ploughing, harrowing and milling is important for wind erosion control. Wind tunnel simulation of soil erosion under ridge tillage with different configuration and flat tillage indicated that ridge tillage decreased wind erosion rates by 20-40 % compared with flat tillage, and the effect was especially significant while wind velocity above 15 m s-1. Differences also existed among six kinds of ridge tillage. For the same RH, wind erosion rate decreased with increasing RBRF. For the same RBRF, wind erosion rate increased with increasing RH. A positive correlation existed between wind erosion rate and SBAR. In addition, Compared with flat tillage, ridge tillage decreased the total amount of sand transported at the height of 0–20 cm and the fraction of sand transported at the height of 0–4 cm, which made plant abrasion caused by blown sand was released. For the same RH, Q0-4 / Q0-20 and Q0-10 / Q0-20 increased with increasing RBRF. For the same RBRF, Q0-4 / Q0-20 and Q0-10 / Q0-20 decreased with increasing RH. Among all the nine kinds of designed treatment, ridge tillage with 3 cm RH and RBRF 1/3 was best in decreasing wind erosion rates and sand transport rate of wind flow near soil surface. Through field observation of blown-sand movement on field surface after moldboard plowing, harrowing and milling respectively, we found the practice of harrowing and milling destroyed non-erodible clods formed by previous moldboard plowing practice, which increased sand transport rate in 0-60 cm, and the increment may reach several tenfold. After the practices of harrowing and milling, critical field length for saturation of blown-sand decreased compared with ploughing soil surface. On ploughing soil surface, the proportion of sand transported in 0-10 cm (Q0-10/Q0-60) at the site of 21 m windward was only 22.12 %, while after harrowing and milling Q0-10/Q0-60 reached 44.82 % at the site of 10 m windward. So we concluded ridge tillage with reasonable configuration and surface clods with enough coverage can resist development of soil erosion and blown sand flow, decrease wind erosion rate, reduce blown sand disaster, which make them be effective measures for wind erosion control.Above all, crop stubble with suitable height and ridge tillage with reasonable configuration were effective measures for wind erosion control in fallow in farming and pastoral zone of northern China. These measures can keep soil surface covered with nonerodible grass or ridge, decrease erosion force of wind flow, prevent sand and dust from being blown. And plowing practice on bare soil surface of farmland before aeolian period can keep soil surface covered with nonerodible clods, which make it an emergency measure for soil wind erosion on farmland in semiarid region of northern China.