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.     

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.     

Fine-earth translocation by tillage in stony soils in the Guadalentin, south-east Spain: an investigation using caesium-134

Tillage erosion is increasingly recognised as an important soil erosion process on agricultural land. In view of its potential significance, there is a clear need to broaden the experimental database for the magnitude of tillage erosion to include a range of tillage implements and agricultural environments. The study discussed in this paper sought to address the need for such data by examining tillage erosion by a duckfoot chisel plough in stony soils on steep slopes in a semi-arid environment. Results of the investigation of coarse fraction (rock fragment) translocation by tillage in this environment have been presented elsewhere and the paper focuses on tillage translocation and erosion of the fine earth. Tillage translocation was measured at 10 sites, representing both upslope and downslope tillage by a duckfoot chisel plough on five different slopes, with tangents ranging from 0.02 to 0.41. A fine-earth tracer, comprising fine earth labelled with ¹³⁴Cs, was introduced into the plough layer before tillage. After a single pass of the plough, incremental samples of plough soil were excavated and sieved to separate the fine earth from the rock fragments. Translocation of the fine-earth tracer was established by analysing the ¹³⁴Cs content of the samples of fine earth. These data were used to establish translocation distances for each combination of slope and tillage direction. Translocation distances of the fine earth were not significantly different from translocation distances of the coarse fraction. For all sites, except uphill on the 0.41 slope, translocation distances were found to be linearly related to slope tangent. The soil flux due to tillage for each site was calculated using the translocation distance and the mass per unit area of the plough layer. For slopes with tangents <0.25, the relationship between soil flux and tangent was linear and the soil flux coefficient derived was 520–660 kg m⁻¹ per pass. This is much larger than the coefficients found in other studies and this high magnitude is attributed to the non-cohesive nature and high rock fragment content of the soil in this investigation. A second contrast with previous studies was found in non-linearity in the relationship between soil flux and tangent when steeper slopes were included. This was a product of variation in plough depth between the steepest slopes and the remainder of the study area. On the basis of the study it is suggested that an improved understanding of tillage erosion may be obtained by considering the dual processes of tillage detachment (mass per unit area of soil subject to tillage) and tillage displacement (equivalent to translocation distance per pass) in assessing, comparing and modelling tillage translocation. An improved model is proposed that recognises the complexity of soil redistribution by tillage, provides a framework for process-based investigation of the controls on tillage fluxes, and allows identification of potential self-limiting conditions for tillage erosion.     

Re-defining tillage erosion: quantifying intensity–direction relationships for complex terrain

Abstract. Current tillage erosion models account for the influence of tillage direction in the magnitude of the soil (tillage) transport coefficient. It is argued here that this is counter-intuitive and causes significant problems in modelling tillage erosion in areas of complex terrain. This article examines whether a re-modelling of tillage erosion is possible that separates tillage direction (an interaction with the landform) from the soil transport coefficient (a measure of tillage intensity representing the combination of implement erosivity and soil erodibility). Experimental data for mouldboard ploughing upslope, downslope and cross-slope at Coombe Barton Farm, Devon are examined. Integration of data for all directions into a single relationship, which relates translocation in the direction of tillage to slope in the direction of tillage and translocation perpendicular to tillage to slope perpendicular to tillage, is not possible using previously published methods of analysis. However, when total translocation distance is regressed against the tangent of the slope at 45° to the tillage direction (bisecting the tillage direction and the direction of overturning) it is found that a single relationship can be used to describe tillage in all three directions. Therefore, this relationship is used to determine a single value of the soil transport coefficient ( k _fTa) for constant soil and implement conditions but different tillage directions. This redefinition of tillage is important both for true estimation of tillage erosion severity, the adirectional coefficient being 40% larger than the directional coefficient, and for modelling of tillage erosion in complex terrain. These improvements are vital when tillage erosion simulation is used to direct soil conservation strategies.     

Soil movement by tillage as affected by slope

Exposure of subsoil material on ridge tops and adjacent sideslopes indicates soil movement away from these positions, i.e. soil erosion. A study was conducted on the University of Minnesota Southwestern Experiments Station to determine if soil movement by tillage could be a contributing factors to the apparent soil erosion present on many ridge tops. Numbered soil movement detection units (11-mm steel hexagonal nuts) were buried 10-cm deep in a grid network in 16 individual plots, on a sideslope with slopes ranging from 1 to 8%. Plots were moldboard plowed and disked in June, and again in August. The direction of tillage was either across the sideslope or up- and downslope. The soil movement detection units were then located with a metal detector, excavated and identified, and distance moved was measured in relation to movement perpendicular and parallel to the direction of tillage. Soil movement was directly related to slope. Movement perpendicular off the moldboard on the direction of tillage was greater than movement perpendicular off the moldboard. Calculations on the angle of movement in relation to tillage direction showed movement toward the downslope position. Results from this study suggest that soil movement by tillage can contribute to soil movement off ridge tops and adjacent sideslopes.     

Modelling tillage erosion in the topographically complex landscapes of southwestern Ontario, Canada

A tillage erosion model was developed for southwestern Ontario based on the relationship between tillage translocation and slope gradient and slope curvature. Two studies of tillage translocation and tillage erosion were used to calibrate this model, one a comparison of upslope and downslope tillage translocation on shoulder slopes, the other an examination of tillage translocation throughout topographically complex landscapes. Two field sites were used for validation of the model. For both sites, past tillage practices were known and past soil erosion was determined using ¹³⁷Cs as an indicator of soil redistribution. The model accurately predicted the pattern of soil redistribution that had occurred within the two field sites. Severe soil loss was observed and predicted on convex landscape positions and soil accumulation was observed and predicted on concave landscape positions. The model accounted for almost all of the soil lost from the convex upper slope positions where tillage erosion was expected to be the dominant erosion process. There was considerable soil loss and accumulation elsewhere in the landscapes which could not be accounted for by the model and was presumed to be primarily the result of water erosion. It was concluded that tillage erosion must be incorporated into soil erosion modelling for the purposes of soil conservation.     

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。     

Characterization of soil profiles in a landscape affected by long-term tillage

Soil movement by tillage redistributes soil within the profile and throughout the landscape, resulting in soil removal from convex slope positions and soil accumulation in concave slope positions. Previous investigations of the spatial variability in surface soil properties and crop yield in a glacial till landscape in west central Minnesota indicated that wheat (Triticum aestivum) yields were decreased in upper hillslope positions affected by high soil erosion loss. In the present study, soil cores were collected and characterized to indicate the effects of long-term intensive tillage on soil properties as a function of depth and tillage erosion. This study provides quantitative measures of the chemical and physical properties of soil profiles in a landscape subject to prolonged tillage erosion, and compares the properties of soil profiles in areas of differing rates of tillage erosion and an uncultivated hillslope. These comparisons emphasize the influence of soil translocation within the landscape by tillage on soil profile characteristics. Soil profiles in areas subject to soil loss by tillage erosion >20 Mg ha⁻¹ year⁻¹ were characterized by truncated profiles, a shallow depth to the C horizon (mean upper boundary 75 cm from the soil surface), a calcic subsoil and a tilled layer containing 19 g kg⁻¹ of inorganic carbon. In contrast, profiles in areas of soil accumulation by tillage >10 Mg ha⁻¹ year⁻¹ exhibited thick sola with low inorganic carbon content (mean 3 g kg⁻¹) and a large depth to the C horizon (usually >1.5 m below the soil surface). When compared to areas of soil accumulation, organic carbon, total nitrogen and Olsen-extractable phosphorus contents measured lower, whereas inorganic carbon content, pH and soil strength measured higher throughout the profile in eroded landscape positions because of the reduced soil organic matter content and the influence of calcic subsoil material. The mean surface soil organic carbon and total nitrogen contents in cultivated areas (regardless of erosion status) were less than half that measured in an uncultivated area, indicating that intensive tillage and cropping has significantly depleted the surface soil organic matter in this landscape. Prolonged intensive tillage and cropping at this site has effectively removed at least 20 cm of soil from the upper hillslope positions.     

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.     

Assessment of tillage translocation and tillage erosion by hoeing on the steep land in hilly areas of Sichuan, China

Most of the tillage erosion studies have focused on the effect of tractor-plough tillage on soil translocation and soil loss. Only recently, have a few studies contributed to the understanding of tillage erosion by manual tillage. Furthermore, little is known about the impact of tillage erosion in hilly areas of the humid sub-tropics. This study on tillage erosion by hoeing was conducted on a purple soil (Regosols) of the steep land, in Jianyang County, Sichuan Province, southwestern China (30°24′N and 104°35′E) using the physical tracer method.

The effects of hoeing tillage on soil translocation on hillslopes are quite evident. The tillage transport coefficients were 26–38 kg m⁻¹ per tillage pass and 121–175 kg m⁻¹ per tillage pass respectively for k₃- and k₄-values. Given that there was a typical downslope parcel length of 15 m and two times of tillage per year in this area, the tillage erosion rates on the 4–43% hillslopes reached 48–151 Mg ha⁻¹ per year. The downslope soil translocation is closely related to slope gradient. Lateral soil translocation by such tillage is also obvious though it is lower than downslope soil translocation. Strong downslope translocation accounts for thin soil layers and the exposure of parent materials/rocks at the ridge tops and on convexities in the hilly areas. Deterioration in soil quality and therefore reduction in plant productivity due to tillage-induced erosion would be evident at the ridge tops and convex shoulders.     

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。     

Tillage translocation and tillage erosivity by planting, hilling and harvesting operations common to potato production in Atlantic Canada

In Canada, the negative impacts of tillage erosion is a growing concern, especially in regions where highly erosive cropping and tillage systems are practiced on highly erodible, topographically complex landscapes. To date, tillage erosion studies have focused primarily on the movement of soil by primary and secondary tillage operations. However, in potato (Solanum tuberosum L.) production there is often considerable soil disturbance that occurs during “tertiary” field operations conducted during the growing season. Therefore, the objective of this project was to generate tillage translocation and erosivity values for implements common to planting, hilling and harvesting operations within intensive potato production systems in Atlantic Canada. Our results show that tertiary tillage operations result in significant soil displacement and can be equally as erosive as primary and secondary tillage operations. Both the planting, cultivating and hilling (PCH) sequence and the harvester moved soil extremely large distances (up to 23.6 and 6.0 m, respectively). In fact, the mean translocated distance of the tilled layer (T_L) and the mass of translocated soil (T_M) of the PCH sequence (0.42 m and 115.9 kg m⁻¹, respectively) and the harvester (0.55 m and 71.7 kg m⁻¹, respectively) are larger than those reported previously for primary and secondary tillage operations in New Brunswick. In addition, the net downslope movement of soil for the PCH sequence and the harvester was approximately 36 and 26 kg m⁻¹, respectively, suggesting that both tertiary tillage operations have the potential to be erosive. A direct relationship was observed between both T_L and T_M and slope gradient for the PCH sequence, but similar relationships were not found for the harvester, even though the harvester moved approximately 30 % more soil downslope than upslope. Linear regression functions were generally improved after including slope curvature in the model, but these results were not always significant. Soil movement by the PCH sequence and harvester were also largely influenced by tillage speed and tillage depth, and future research is needed under controlled conditions to determine whether it is changing topography or the variability in tillage speed and depth across the landscape in response to changing topography that is driving tillage erosion within mechanized agricultural systems. It is clear that tertiary tillage operations must be considered when developing best management practices to improve soil conservation strategies for potato production systems in Canada and worldwide.     

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.     

Soil erosion under simulated rainfall in relation to phenological stages of soybeans and tillage methods in Lages, SC, Brazil

Soil tillage may increase vulnerability to water erosion, whereas no tillage and other conservation cultivation techniques are viewed as strategies to control soil erosion. The objective of this research was to quantify runoff and soil losses by water erosion under different soil tillage systems at the Santa Catarina Highlands, southern Brazil. A field study was carried out using a rotating-boom rainfall simulator with 64 mm h⁻¹ rainfall intensity on a Typic Hapludox, between April 2003 and May 2004. Five rainfall tests were applied along successive cropstages. Surface cover was none (fallow) or soybean (Glycine max, L.). Five treatments were investigated, replicated twice. These treatments were conventional tillage on bare soil (BS) as a control treatment and the following treatments under soybean: conventional tillage (CT), no tillage over burnt crop residues on never before cultivated land (NT-B), no tillage over desiccated crop residues, also on never before cultivated land (NT-D) and traditional no tillage over desiccated crop residues on a soil tilled 4 years before this experiment (NT-PT). Water losses by surface runoff seemed to be more influenced by vegetative crop stadium than by tillage system and consequently a wide range of variation in surface runoff was found, following successive cropstages. The most efficient tillage system in reducing surface runoff and soil losses was no tillage, particularly the NT-PT treatment. Sediment losses were more influenced by tillage system than water losses. In the NT-B, NT-D and NT-PT treatments the rate of sediment losses along the crop vegetative cycle showed a tendency to increase from the first to the second cropstages and later to decrease from the third cropstage onwards. In the conventionally tilled treatment (CT) soil losses were greater than in any of the no tillage treatments (NT-D, NT-B and NT-PT) during the initial growth periods, but at the end of the vegetative period differences in sediment rates between tilled and non-tilled treatments tended to be smaller. In the BS control treatment, soil losses progressively increased following the vegetative growth season of soybean.     

Simulation and 137Cs tracer show tillage erosion translocating soil organic carbon,phosphorus, and potassium

Research on how tillage‐induced soil redistribution affects soil properties is limited for complex slopes in nonmechanized agricultural areas. The objectives of this study are (1) to examine the vertical redistribution of soil organic C (SOC), extractable P and K induced by tillage on a complex slope, (2) to assess the effects of tillage erosion on soil profile properties, and (3) to elucidate the variations in soil properties induced by both vertical mixture and downslope transport of soil within the landscape. Simulated tillage was conducted in the Yangtze Three Gorges Reservoir Area, China. The ¹³⁷Cs data showed that intense tillage caused the soil vertical mixture and downslope transport. The redistribution of ¹³⁷Cs and soil constituents varied with the number of tillage passes and location in relation to curvature. SOC was completely depleted with the disappearance of soil profiles at the summit position, while SOC concentrations decreased by 26% for the till layer and increased by 29% for the sublayer at the toeslope position for the 15‐tillage operation, as compared with those of pretillage. The vertical redistribution of extractable P and K followed a similar pattern to that of SOC. The gap and variation in soil constituents between the till layer and sublayer declined after tillage, suggesting that the mixing effect of tillage attenuates the variability of soil properties in the vertical direction. Net loss and gain of soil constituents occurred at the summit and toeslope positions, respectively, suggesting that the downslope transport of soil induced by tillage accentuates the variability of soil properties in the lateral direction.     

降雨条件下耕作方式对地表糙度的溅蚀效应

地表糙度是影响坡耕地土壤侵蚀的主要因素之一,为了进一步明确耕作方式对地表糙度的侵蚀效应,该文通过室内人工模拟降雨的方法,就单雨强与组合雨强条件下耕作方式对溅蚀的作用以及地表糙度的变化进行了研究。结果表明,从对照坡面,经耙耱地、人工锄耕、人工掏挖到等高耕作方式的坡面,在雨强0.62 mm/min条件下,不同耕作方式坡面向上坡溅蚀量呈先增加再减小的变化,向下坡和总溅蚀量均呈先增加再减小最后增加的变化;除耙耱地外,其他耕作方式坡面的地表糙度呈减小的变化。在雨强1.53 mm/min条件下,不同耕作方式坡面向上坡、向下坡和总溅蚀量均呈先增加再减小最后增加的变化;地表糙度与对照坡面相反,均呈增加的变化。组合雨强条件下,随降雨强度的增加,耙耱地总溅蚀量与地表糙度呈一直增加的变化趋势;其他耕作方式下,随降雨强度的增加,坡面总溅蚀量呈先增加后减小的变化趋势,地表糙度却呈先减小后增大的变化。这为揭示地表糙度的侵蚀特征提供了一定的理论依据,同时也可服务于黄土高原坡耕地的水土流失治理。     

A comparison between seasonal changes in soil water storage and penetration resistance under conventional and conservation tillage systems in Aragón

Low and extremely variable precipitations limit dryland crop production in the semi-arid areas of Aragón (NE Spain). These areas are also affected by high annual rates of topsoil losses by both wind and water erosion. A long-term experiment to determine the feasibility of conservation tillage in the main winter barley production areas of Aragón was initiated in 1989 at four locations, three on loam to silt loam soils (Xerollic Calciorthid) and one on a silty clay loam (Fluventic Ustochrept), receiving between 300 and 600 mm of average annual rainfall. In this study, we compared, under both continuous cropping and cereal-fallow rotation, the effects of conventional tillage (mouldboard plough) and two conservation tillage systems, reduced tillage (chisel plough) and no-tillage, on soil water content and penetration resistance during the first two growing seasons. Whereas reduced and conventionally tilled treatments generally had similar soil water content during the experimental period, the effects of no-tillage were inconsistent. No-tilled plots had from 26% less to 17% more stored soil water (0–80 cm) than conventional tilled plots at the beginning of the growing season. In contrast to the conventional and reduced tillage treatments, penetration resistances were between 2 and 4 MPa after sowing in most of the plough layer (0–40 cm) under no-tillage at all sites. Fallow efficiencies in moisture storage in the cereal-fallow rotation, when compared with the continuous cropping system, ranged from −8.7 to 12%. The highest efficiencies were recorded when the rainfall in the months close to primary tillage exceeded 100 mm. Since this event is very unlikely, long fallowing (9–10 months) appears to be an inefficient practice for water conservation under both conventional and conservation management. Our results suggest that, up to now, only reduced tillage could replace conventional tillage without adverse effects on soil water content and penetration resistance in the dryland cereal-growing areas of Aragón.     

岩溶区坡地耕作侵蚀过程中的土壤再分布研究

对耕作侵蚀引起的土壤空间再分布进行研究,有利于改革不合理的耕作方式和治理坡耕地水土流失。本文以重庆市中梁山为例用示踪法对坡耕地进行试验研究。结果表明:随着坡度的增大,耕作后示踪剂在示踪区的含量越来越少;它的最大值出现的位置离基线越来越远,值越来越小;沿耕作方向移动的距离越来越远。这种规律性以锄头和铁锹顺坡明显,等高和踩锹顺坡不明显。从本区耕作侵蚀的角度考虑,等高耕作方式明显要优于顺坡耕作;在顺坡耕作中踩锹优于锄头和铁锹。最后还结合岩溶山区特殊的自然环境条件,讨论了耕作侵蚀对石漠化的影响。     

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.     

田块尺度顺坡垄作改等高垄作提高黑土有机质含量

为了明晰等高垄作后对坡耕地土壤有机质的恢复作用,选取一块面积为1.4 hm2的典型黑土坡耕地,采用标准栅格法,同位大样点取样调查了改垄前和改垄10 a后土壤有机质和含水率等性状的变化。结果表明:1)与经典统计学相比,地统计学通过变程、块金值与基台值的比值以及插值绘制空间分布图,能够从全坡面更好地反映改垄前后性状的空间变化;2)等高改垄10 a后,垄台土壤含水率变程由510.7 m降低到193.2 m,块金值与基台值的比值由11.7%升至46.9%,空间相关性强度由强烈变为中等,水分再分配降低;3)耕层土壤有机质总体增加了2.61 g/kg,提升了8.4%,只在坡中上部西侧小区的部分区域降低了3.7%;4)土壤全氮含量减少了0.04 g/kg,降低了2.8%。上述结果表明,对于严重侵蚀的坡耕地,改顺坡垄为等高垄作,可弱化性状空间相关性,对土壤有机质具有恢复作用,但应适当增加化肥氮素的施用量,对东北黑土区坡耕地水土流失治理具有指导意义。