紫色土坡地犁耕方向对耕作侵蚀的影响

采用磁性示踪法测定等高犁耕、向下犁耕和向上犁耕的耕作位移和土壤位移量,定量评价耕作方向对牛拉犁耕作侵蚀的影响,比较四川紫色土区牛拉犁常用的等高犁耕与上下坡交替犁耕的耕作侵蚀强度。结果表明:在研究区土壤和牛拉三角铧式犁耕作条件下,向下犁耕的耕作位移明显大于向上犁耕和等高犁耕,坡度对向下犁耕土壤位移量影响显著,而对向上犁耕和等高犁耕影响较小;等高犁耕和上下坡交替犁耕引起的土壤位移量分别为40.97~70.42kg/m和0.68~34.58kg/m;耕作方向由等高犁耕改为上下坡交替犁耕可显著减小耕作侵蚀,当坡度为10%时,耕作侵蚀可减少98.5%,当坡度为40%时,耕作侵蚀可减少33.3%。对于紫色土区牛拉犁耕作,上下坡交替犁耕是减少耕作侵蚀和防治土壤退化的一种行之有效的方法。     

紫色土坡地旋耕机耕作侵蚀特征

耕作侵蚀的过程机制和防治技术研究是我国现阶段水土保持科学与技术的重点研究领域,关于小型旋耕机耕作的土壤再分布过程和影响因素研究较少.应用磁性示踪法研究旋耕机等高耕作、向下耕作和向上耕作的土壤再分布模式和强度,查明耕作速度对旋耕机耕作侵蚀的影响.结果表明:不同耕作方向下旋耕机单次耕作过程中均引起土壤同时发生向上坡和向下坡移动,且均导致土壤发生向下坡净位移;不同耕作速度时等高耕作和向上耕作土壤净位移与坡度均呈显著正相关(P＜0.01),而向下耕作二者无显著相关性(P＞0.05);土壤净位移量表现为快挡等高耕作(11.53 kg/m)＞快挡向下耕作(11.40kg/m)＞快挡向上耕作(7.59kg/m)＞慢挡向下耕作(7.33 kg/m)＞慢挡等高耕作(6.87 kg/m)＞慢挡向上耕作(6.29 kg/m);快挡时上下坡交替耕作的耕作侵蚀速率小于等高耕作,但慢挡时二者相当.旋耕机耕作相比传统耕作机具的耕作侵蚀明显下降,其推广应用对于防治紫色土坡地耕作侵蚀和土壤退化有重要作用.     

等高犁耕对黄土坡耕地坡形与坡度的影响

为了明确等高犁耕条件下黄土坡耕地地形与坡度的变化特征,基于6个坡度(3°,5°,10°,15°,20°,25°)和5个耕作强度(6,12,18,24,30次)的组合,开展模拟耕作试验,利用测针法获取耕作后地表高程数据,探讨耕作强度和坡度对黄土直线形坡演化特征的影响。结果表明,在等高向下犁耕条件下,不同坡度的直线坡随着耕作强度的增加逐渐向“∽”形复合坡演化。同一坡度下,随着耕作强度的增加,坡脚延伸,整体小区投影坡长增大,坡脚高程增加幅度大,堆积现象明显,坡度大幅度减小;坡中高程增加,逐渐抬起坡度减小;坡顶形成的新分水岭的高程和位置随之减小和向下推移,直接侵蚀速率逐渐减小且趋于稳定。坡度通过影响土壤运动能力控制耕作时土壤的分布。因此坡度越大,单次耕作后坡形的变化越明显,直接侵蚀速率越大。研究结果有助于更加深入了解耕作侵蚀对坡耕地地形的影响,为控制坡耕地土壤侵蚀提供理论依据。     

东北黑土区典型坡面耕作侵蚀定量分析

东北黑土区水土流失主要集中在坡耕地,以往研究多关注水蚀而忽略了耕作侵蚀的存在。为印证并定量描述黑土耕作侵蚀,该文采用物理示踪法,测定了典型坡耕地耕作位移量及其分布格局。结果表明:铧式犁耕作后示踪剂沿耕作方向发生扩散,上坡耕作示踪剂集中分布在0~20 cm范围,而下坡耕作示踪剂集中分布在0~20和50~150 cm。一次耕作引起的耕作位移量为32.68~134.14 kg/m,耕作迁移系数234 kg/m。坡度是影响耕作位移的重要因素,二者呈显著的正相关关系,且对上坡耕作的影响大于下坡耕作。研究区耕作年侵蚀速率0.4~11.0 Mg/(hm2·a),凸起的坡背、坡肩处及坡度较大的位置侵蚀严重。虽然黑土区坡度较小,但由于耕作深度大,速度快,耕作侵蚀严重,应引起足够重视。     

黄土高原丘陵沟壑区坡地耕作方式对土壤侵蚀的影响研究

为研究耕作方式对坡耕地土壤侵蚀的影响,在黄土高原丘陵沟壑区选取典型坡耕地,采用示踪块法,对畜力横向犁耕、人力顺向掏挖、人力逆向锄耕和机械横向犁耕4种主要耕作方式在5°,10°,15°3种坡度条件下进行耕作侵蚀试验。结果表明:不同坡度条件下,耕作方式对土壤颗粒位移的影响较为显著,畜力横向犁耕、人力顺向掏挖和机械横向犁耕随坡度增大,示踪块位移增大;而人力逆向锄耕中,耕作使土块向上坡方向移动,但受重力影响,坡度越大,移动距离越小。同一坡度条件下,耕作模式所产生的水平位移由大到小依次是机械横向犁耕畜力横向犁耕人力顺向掏挖人力逆向锄耕。4种耕作方式中,机械横向犁耕造成土壤颗粒位移和耕作侵蚀量最大,人力逆向锄耕影响最小。为减少耕作侵蚀,针对坡耕地尽可能采用少耕或免耕方式,以减少耕作侵蚀,在不增加劳动强度的情况下,10°以上坡耕地可采用人力逆向锄耕模式耕作。     

旋耕机耕作对紫色土碳氮垂直分布过程的影响

利用在土壤表面人为添加钛铁矿粉以示踪表层土壤垂直和顺坡再分配过程,通过对比耕作前与模拟耕作20次、40次土壤有机碳和全氮垂直分布特征,研究紫色土旋耕机等高耕作所产生的土壤顺坡和垂直搬运耦合作用对有机碳、全氮垂直分布过程的影响机制。结果显示:强烈耕作后坡顶侵蚀深度超过原土壤剖面厚度,但土壤剖面厚度依然与耕作深度相当,这是由于耕作对坡顶土壤起着顺坡搬运(耕作侵蚀)和垂直搬运(破碎母岩)的双重作用。磁性示踪剂的深度分布显示出耕作引起表层土壤垂直向下迁移,但不同坡位垂直分布机制不同。坡顶土壤有机碳和全氮浓度明显减小,这是由于强烈的耕作侵蚀向下坡搬运耕层土壤,同时耕作垂直搬运引起母岩碎屑向耕层混入产生稀释作用;坡趾表层0—5 cm土壤有机碳和全氮浓度减小,但是5—20 cm明显增加,表明耕作侵蚀引起来自上坡的低浓度土壤在坡趾堆积。这些结果表明旋耕机等高耕作下土壤同时发生顺坡传输与垂直迁移,两者相互作用导致耕作侵蚀区和耕作沉积区呈现出明显不同的有机碳、全氮垂直分布模式。     

我国南方丘陵区土壤耕作侵蚀的定量研究

通过采用示踪法对四川丘陵区坡耕地的耕作试验研究 ,获得了土壤耕作位移和土壤耕作侵蚀的直接证据 ,确定了耕作侵蚀是四川丘陵区土壤流失的原因之一。试验结果指出 ,四川丘陵区单次耕作的土壤位移量为 43.70～ 6 4.47kg/ m;平均土壤耕作侵蚀速率为 6 5 .0 5～ 97.0 5 t/ hm2 .a。土壤耕作位移受地面坡度的影响十分明显 ,平均位移距离与坡度间呈显著正相关关系。耕作侵蚀速率主要取决于坡体长度 ,只有在坡体长度相同的条件下 ,耕作侵蚀速率才随坡度的增大而增加     

紫色土坡耕地土壤物理性质空间变异对土壤侵蚀的响应

为了研究不同坡度和坡长的耕地上土壤侵蚀对土壤物理性质空间变异的影响,通过地形测量、137 Cs示踪、土壤物理性质分析等方法对川中丘陵紫色土区土壤物理性质对土壤侵蚀的响应进行了研究,结果表明：在中等坡度（16.60%～25.10%）的梯坡地上,耕作侵蚀处于主导地位,是导致耕层土壤物理性黏粒含量和容重在梯坡地上总体差异不大（CV＜6.3%）,且与137Cs含量不相关的主要原因;在已退耕还林的陡梯坡地上（35.60%）,水蚀占据主导地位,导致耕层土壤物理性黏粒含量和容重均与137Cs的含量显著相关。在长坡耕地上(10.10%),具有分选搬运能力的水力侵蚀占据主导地位,致使耕层土壤物理性黏粒含量与137Cs的含量具有显著的相关关系,而容重却与137Cs含量没有显著的相关关系。川中丘陵区坡耕地上,耕作侵蚀和水蚀共同作用于土层深度,使土层深度在坡顶、上坡最浅,在坡脚最深,顺坡向下逐渐增加。因此,在川中丘陵区不同坡长的坡耕地上,占主导地位的土壤侵蚀类型导致坡耕地上土壤物理性质出现相应的变化。     

耕作侵蚀及其对土壤肥力和作物产量的影响研究进展

在坡耕地景观内，由于农耕工具和重力作用而引起的耕作位移使土壤发生向下坡运动或向上坡运动(依赖于耕作方向)，导致净余土壤量向下坡传输、堆积，重新分配，从而形成耕作侵蚀。试验研究表明耕作侵蚀是坡耕地的主要侵蚀形式之一，耕作侵蚀发生最严重的区域是坡度较大、坡体短的坡耕地。该文就耕作侵蚀的概念、发生机理、典型的耕作侵蚀模型的发展，以及耕作侵蚀对土壤肥力和作物产量影响的研究现状作了简要论述，特别总结了针对中国的地貌和耕作工具特征而进行的耕作侵蚀的研究成果。指出在一定的景观范围内，耕作侵蚀是十分严重的，甚至其严重程度已经超过了水蚀。但是相对于水蚀而言，耕作侵蚀研究还很少，因此加强耕作侵蚀的研究是十分必要的。只有这样才能正确评价农耕地侵蚀状况，准确制定土壤保持措施和采用减少耕作侵蚀力的耕作工具，从而有效地控制土壤侵蚀。     

不同逆坡耕作强度对干热河谷区坡耕地水蚀的影响

为了研究不同逆坡耕作强度导致的土壤位移对坡面水蚀的影响,以金沙江干热河谷区坡面径流小区为研究对象,在径流小区5°,10°,15°坡面上,进行单宽流量为0.6 m^2/h的放水试验。在10°坡面的下坡位置设置0.05,0.10,0.20 m土层深度,分别代表连续耕作80,69,46年导致下坡位置土壤损失土层变薄情况。通过收集径流小区出口的产流量和产沙量,研究在不同坡度上的不同逆坡耕作强度导致的土壤位移对坡面产流率、产沙率、总流量和总产沙量的影响。结果表明:(1)在10°坡面,耕作年限越长,产流越快,不同耕作强度(年限)的产流率、总产流量、产沙率和总产沙量均表现46年<69年<80年的变化趋势,说明长期逆坡耕作导致的土壤位移加速了坡面水蚀的发生;(2)在耕作69年的坡面,坡度越大,产流越快。在测定坡度范围,产流率、总产流量、产沙率和总产沙量均表现出5°<10°<15°的变化趋势,即坡度的增加明显增大了坡面水蚀;(3)随耕作侵蚀强度的增大,坡面产流率与产沙率间的指数增长关系越显著,而坡度的增大弱化了水沙指数函数关系。研究成果可为揭示干热河谷区逆坡耕作强度和坡度对水蚀的作用机理提供参考。     

重庆中梁山岩溶区耕作侵蚀影响因素研究

在重庆市中梁山岩溶区用示踪法对坡耕地进行耕作试验研究。结果表明:锄头和铁锹耕作引起的土壤位移距离、位移量与坡度呈正相关,而踩锹引起的土壤位移距离、位移量则与含水量具有一定的相关性。在顺坡耕作时铁锹引起的土壤位移距离、位移量与锄头相近,但它们远远大于踩锹;等高耕作时铁锹引起的土壤位移距离、位移量是锄头的1.3~3.8倍左右。铁锹顺坡耕作引起的土壤位移距离、位移量是它等高耕作的2~2.4倍;锄头顺坡耕作引起的土壤位移距离、位移量是它等高的3~8.8倍。引起土壤位移量的大小顺序依次是:锄头顺坡>铁锹顺坡>铁锹等高>锄头等高>踩锹顺坡。     

紫色土坡地土壤性质对耕作侵蚀的影响

[目的]揭示土壤性质对耕作侵蚀土壤的敏感性,为紫色土区域采取适宜的耕作措施提供依据。[方法]利用磁性示踪技术定量旋耕机上下耕作和等高耕作的土壤耕作位移和土壤位移量,选取土壤容重、土壤含水量、土壤有机质、土壤全氮、土壤有效磷、土壤抗剪强度和土壤紧实度等土壤理化性质和力学性质指标,研究土壤性质对旋耕机上下耕作和等高耕作的耕作侵蚀的影响特征。[结果]旋耕机上下耕作和等高耕作的土壤净位移和净位移量不仅受坡度影响,也受土壤性质的影响。土壤力学性质和土壤物理性质对旋耕机耕作侵蚀有显著影响,对于上下耕作的土壤抗剪强度、土壤紧实度和土壤容重与土壤净位移量呈显著正相关。对于等高耕作措施的土壤抗剪强度、土壤紧实度、土壤容重和土壤含水量与土壤净位移量呈显著正相关,其他指标关系不显著。[结论]土壤抗剪强度、土壤紧实度和土壤容重可以作为评价耕作侵蚀的土壤可蚀性指标。     

Assessment of tillage erosion rates on steepland Oxisols in the humid tropics using granite rocks

Soil translocation by tillage may be an important factor in land degradation in the humid tropics. The objective of this study was to evaluate tillage-induced soil translocation on an Oxisol with 25% and 36% slopes in Claveria, Philippines for three tillage systems: contour moldboard plowing (CMP), moldboard plowing up and downslope (UMP), and contour ridge tillage (CRT). Small rocks 3–4 cm in “diameter” were used as soil movement detection units (SMDU). The SMDUs were placed at 10 cm intervals in a narrow 5-cm-deep trench near the upper boundary of each plot, the position of each rock recorded, and the trench backfilled. Five tillage operations used to produce one corn crop were performed during a one month period: two moldboard plowing operations for land preparation (except for CRT), one moldboard plowing for corn planting, and two inter-culture (inter-row cultivation) operations. After these operations, over 95% of the SMDU were recovered manually and their exact locations recorded. Mean annual soil flux for the 25% slope was 365 and 306 kg m⁻¹ y⁻¹ for UMP and CMP, respectively. For the 36% slope, comparable values were 481 and 478 kg m⁻¹ y⁻¹. Estimated tillage erosion rates for the 25% slope were 456 and 382 Mg ha⁻¹ y⁻¹ for UMP and CMP, respectively, and increased to 601 and 598 Mg ha⁻¹ y⁻¹, respectively, for the 36% slope. The mean displacement distance, mean annual soil flux, and mean annual tillage-induced soil loss for both slopes were reduced by approximately 70% using CRT compared to CMP and UMP.     

Measurement and modelling of the effects of initial soil conditions and slope gradient on soil translocation by tillage

Tillage erosion studies have mainly focused on the effect of topography and cultivation practices on soil translocation during tillage. However, the possible effect of initial soil conditions on soil displacement and soil erosion during tillage have not been considered. This study aims at investigating the effect of the initial soil conditions on net soil displacement and the associated erosion rates by a given tillage operation of a stony loam soil. Tillage erosion experiments were carried out with a mouldboard plough on a freshly ploughed (pre-tilled) soil and a soil under grass fallow in the Alentejo region (Southern Portugal).

The experimental results show that both the downslope displacement of soil material and the rate of increase of the downslope displacement with slope gradient are greater when the soil is initially in a loose condition. This was attributed to: (i) a greater tillage depth on the pre-tilled soil and (ii) a reduced internal cohesion of the pre-tilled soil, allowing clods to roll and/or slide down the plough furrow after being overturned by the mouldboard plough.

An analysis of additional available data on soil translocation by mouldboard tillage showed that downslope displacement distances were only significantly related to the slope gradient when tillage is carried out in the downslope direction. When tillage is carried out in the upslope direction, the effect of slope gradient on upslope displacement distances was not significant. This has important implications for the estimation of the tillage transport coefficient, which is a measure for the intensity of tillage erosion, from experimental data. For our experiments, estimated values of the tillage transport coefficient were 70 and 254 kg m⁻¹ per tillage operation for grass fallow and pre-tilled conditions, respectively, corresponding to local maximum erosion rates of ca. 8 and 35 Mg ha⁻¹ per tillage operation and local maximum deposition rates of ca. 33 and 109 Mg ha⁻¹ per tillage operation.     

Ridge tillage and contour natural grass barrier strips reduce tillage erosion

Large amounts of soil are eroded annually from tilled, hilly upland soils in the humid tropics. Awareness has been increasing that much of this erosion may be due to tillage operations rather than water-induced soil movement. This field study estimated soil translocation and tillage erosion for four tillage systems on Oxisols with slope gradients of 16–22% at Claveria, Misamis Oriental, Philippines. Soil movement was estimated using ‘soil movement tracers' (SMT) which consisted of painted 12-mm hexagonal steel nuts. The SMT were buried in three replicate plots of the following tillage treatments: (1) contour moldboard plowing in the open field (MP-open); (2) contour ridge tillage in the open field (RT-open); (3) contour moldboard plowing plus contour natural grass barrier strips (MP-strip); and (4) contour natural grass barrier strips plus ridge tillage (RT-strip). Two hundred SMT were placed at the 5-cm depth at 5-cm spacings on 10 rows and 20 columns in two microplots within each plot. The microplots were oriented with the boundaries running downslope and along the contour of each 8-m-wide × 38-m-long (downslope) tillage plot. After tilling the land for four successive corn (Zea mays L.) crops (20 tillage operations), the SMT were manually excavated and their positions recorded. Recovery of SMT ranged from 82% to 85%. Displacement of SMT was directly related to slope length, percent slope, and tillage method. Mean displacement distance of SMT during the four corn growing seasons was 3.3 m for MP-open, 1.8 m for RT-open, 1.5 m for the RT-strip, and 2.2 m for MP-strip. Based on tillage operations associated with two corn crops per year, mean annual soil flux was estimated to be 241, 131, 158 and 112 kg m⁻¹ for MP-open, RT-open MP-strip, and RT-strip, respectively. Compared to the mean annual soil loss for MP-open of 63 Mg ha⁻¹, soil loss was reduced by 30%, 45%, and 53% for the MP-strip, RT-open, and RT-strip systems, respectively. Both ridge tillage and natural grass barrier strips reduced soil displacement, soil translocation flux, and tillage erosion rates.     

The effect of tillage direction on soil redistribution by mouldboard ploughing on complex slopes

Seven mouldboard ploughing experiments were conducted to systematically investigate the effect of different tillage directions on soil redistribution on hillslopes. The present study included tillage directions other than parallel to the gradient or along the contour, that is, in our experiments the slope gradient changed simultaneously in tillage and in turning direction. Using physical tracers we developed a model of the two-dimensional tracer displacement as a function of topography and tillage variables. The displacements in tillage and in turning direction were separately described as 2nd degree polynomials in both tillage and in turning directions. This model fully accounted for the directionality of tillage. Displacement in turning direction additionally depended on tillage depth, while that in tillage direction was affected by tillage speed and soil bulk density. We found a large effect of tillage directionality on soil redistribution, and tillage at 45° to the gradient turning soil upslope was the least erosive tillage direction. We obtained non-linear relationships between soil redistribution and profile curvature, instead of the linear relationships reported previously. Consequently tillage erosivity varied in tillage direction and a unique tillage transport coefficient could not be obtained for all tillage directions.     

Influences of tillage operations on soil translocation over sloping land by hoeing tillage

Very few studies have investigated the factors affecting soil displacement and tillage erosion by hoeing tillage. This study adopted a magnetic tracer method to investigate the influences of hoe form and tillage depth on soil translocation over steep hillslopes in Southwest China using a new type of magnetic tracer, i.e., ilmenite powder. Ilmenite powder enhanced the magnetic sensitivity of soil at the end position of tracer distribution, and improved the accuracy and efficiency of tillage translocation measurements. Tillage translocation by wide and perforated hoes was found to be significantly correlated with slope gradient (P < 0.01), however, no significant correlation was found for narrow and bidentate hoe tillage (P > 0.05). Compared with wide hoes, the tillage erosion rates resulting from the use of narrow, perforated and bidentate hoes were reduced by 12.4%, 11.0%, and 16.3%, respectively, indicating that changes in hoe forms resulted in a marked decrease in downslope soil translocation and tillage erosion. Tillage erosion rate decreased by 64% when the tillage depth was reduced from 0.26 to 0.14 m. These results suggest that innovations in hoe form and reductions in tillage depth are important means to manage tillage erosion due to hoeing.     

Assessment of tillage erosion by mouldboard plough in Tuscany (Italy)

This study was designed to characterise the soil translocation effect induced by mouldboard ploughing with an implement traditionally used in the Tuscany region (Central Italy). We discuss the results of a set of field experiments performed to measure soil displacement along slopes of varying gradient in different directions and at several depths of tillage. Using the Soil Erosion by Tillage (SETi) model, soil translocation patterns for different tillage scenarios were analysed, with special attention paid to the effects of the direction and depth of tillage on the extent and spatial pattern of soil movement. The lateral slope gradient S_P and tillage depth D were found to be the dominant controlling factors for total soil displacement. The effect of the slope gradient in a direction parallel to tillage S_T was much less pronounced. These findings reveal the importance of the asymmetric nature of the soil movement produced by mouldboard ploughing and the predominant effect of the lateral displacement d_P on the actual trajectory of soil motion. Results demonstrate that spatial patterns of soil redistribution due to mouldboard ploughing are highly variable and depend on the particular characteristics of the implement used. This dependence is so strong that maximum downslope soil translocation can occur during both, contour tillage or up–down tillage. For this particular mouldboard plough, maximum downslope soil transport took place at a tillage direction ca. 70° and not when tillage was conducted along the steepest slope direction (0°). These findings highlight the potential of the combined approach applied. The physically based SETi model can be properly calibrated using a relatively limited dataset from field experiments. Once calibrating, the SETi model can then be used to generate synthetic tillage translocation relationships, which can predict the intensity and spatial pattern of soil translocation over a much wider range of tillage scenarios than the particular experimental conditions, in terms of topography complexity (slope gradients and morphology) and the direction and depth of tillage. These synthetic relationships are useful tools for evaluating strategies designed to reduce tillage erosion.