土壤薄片中石英颗粒分布的分形特征

土壤中石英颗粒的粒度分布对揭示母质来源和模拟土壤结构等具有重要意义。本文根据石英的光学性质,利用数字图像处理技术提取土壤薄片中的石英颗粒信息,并应用分形维数来表征土壤薄片中石英颗粒的分布特征。采集免耕和翻耕处理下土壤样品并制作成土壤薄片,利用偏光显微镜和数字图像处理技术提取土壤薄片中石英颗粒,应用Sigma ScanPro5软件统计了石英颗粒的数量、大小和形状等信息,研究土壤薄片中石英颗粒的数量分形特征;并分析了其同石英颗粒数量、面积和平均半径等的关系。结果表明石英颗粒的数量分布具有明显的分形特征,分形维数在1.60～2.18之间,分形维数同薄片中石英颗粒的总面积和平均半径呈负相关。免耕处理下表层土壤石英颗粒的数量分形维数高于底层,而翻耕处理下则呈相反的趋势。免耕和翻耕措施下土壤薄片中石英颗粒的数量分形维数在0～5和10～15cm层次之间没有显著差异,但是在20～25cm层次,翻耕处理分形维数高于免耕处理,说明耕作措施会加速土壤矿物质的风化和破碎并改变石英颗粒在土壤剖面中的分布。     

青岛市新机场建设耕作层土壤质量评价与剥离深度的确定

[目的]探索青岛市新机场耕作层土壤剥离的土壤质量评价方法,并根据土壤质量等级确定耕作层土壤剥离深度,为编制耕作层土壤剥离利用方案提供基础。[方法]依据指标设计原则,对耕作层土壤剥离理念及其目标要求进行分析,提出土壤质量评价指标体系。采用模糊隶属度模型评价土壤肥力,采用内梅罗综合污染指数评价土壤重金属及有机物污染状况,采用SQI指数对土壤综合质量进行评价,划分土壤质量等级,从而确定耕作层土壤剥离深度。[结果]1,3,4,5,8,11,12号采样点耕作层土壤质量等级为一级,2,6,9号采样点耕作层土壤质量等级为二级,7,10号采样点耕作层土壤质量等级为为三级。[结论]一级土壤质量最好,耕作层平均厚度为20cm。建议的土壤剥离深度为30cm;二级土壤质量较好,耕作层平均厚度为20cm,建议对新机场建设项目损毁占用土地的耕作层土壤剥离,土壤剥离深度为20cm;三级土壤质量中等,耕作层平均厚度为20cm,选择性的对新机场建设项目损毁占用土地的部分优质耕作层土壤按层次剥离,土壤剥离深度为10cm。     

基于线结构激光传感器的土壤表面粗糙度测量方法研究

土壤表面粗糙度是农作物种植、灌溉和收获等田间管理必须考虑的作业参数,也是精准农业发展中亟待解决的关键问题之一。针对土壤表面粗糙度缺乏快速检测手段的问题,提出一种基于线结构激光传感器的土壤表面粗糙度测量方法。利用半导体红光激光器、CCD工业相机、计算机及支架等构建测量系统,采集土壤样本的表面图像数据,借助MATLAB获取其三维点云模型,实现土壤表面的三维曲面建模并计算曲面面积。定义土壤表面三维曲面面积与其平面面积的比值为表征土壤表面粗糙度的量,并通过对比4个颗粒度土壤样本的该值范围,确定了判别样本表面粗糙度的阈值。利用3种土槽旋耕土壤表面样本对系统和算法进行验证,比值处于1.214～1.939之间,检测结果均与样本实际特征相符合。该方法能够检测和判断土壤表面的颗粒粗糙程度。     

Soil structure and the effect of management practices

To evaluate the impact of management practices on the soil environment, it is necessary to quantify the modifications to the soil structure. Soil structure conditions were evaluated by characterizing porosity using a combination of mercury intrusion porosimetry, image analysis and micromorphological observations. Saturated hydraulic conductivity and aggregate stability were also analysed.

In soils tilled by alternative tillage systems, like ripper subsoiling, the macroporosity was generally higher and homogeneously distributed through the profile while the conventional tillage systems, like the mouldboard ploughing, showed a significant reduction of porosity both in the surface layer (0–100 mm) and at the lower cultivation depth (400–500 mm). The higher macroporosity in soils under alternative tillage systems was due to a larger number of elongated transmission pores. Also, the microporosity within the aggregates, measured by mercury intrusion porosimetry, increased in the soil tilled by ripper subsoiling and disc harrow (minimum tillage). The resulting soil structure was more open and more homogeneous, thus allowing better water movement, as confirmed by the higher hydraulic conductivity in the soil tilled by ripper subsoiling. Aggregates were less stable in ploughed soils and this resulted in a more pronounced tendency to form surface crust compared with soils under minimum tillage and ripper subsoiling.

The application of compost and manure improved the soil porosity and the soil aggregation. A better aggregation indicated that the addition of organic materials plays an important role in preventing soil crust formation.

These results confirm that it is possible to adopt alternative tillage systems to prevent soil physical degradation and that the application of organic materials is essential to improve the soil structure quality.     

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.     

EFFECTS OF TILLAGE AND STUBBLE MANAGEMENT ON THE STRUCTURE OF A SWELLING SOIL

A method, described previously, is used to quantify the macrostructure within the surface layers of swelling soil. Dissimilarity coefficients are defined and used to quantify soil structural differences resulting from different treatments. Structural differences over small increments in depth are resolved. Effects resulting from different tillage and stubble management practices are distinguished. Differences resulting from burning or retention of stubble had at least as great an effect as tillage practice on the void and aggregate size distributions. However, tillage increased the macro-porosity. The structures of two mechanically-prepared seed beds are compared with the structure of soil on tillage and stubble management trials where seed beds had not been prepared. It is shown in Appendix I that the structures measured on the two sections through each impregnated soil sample are essentially independent. A method is presented in Appendix II for converting the structural transition probabilities at unit spacing (e.g. 0.5 mm) to transition probabilities at double spacing (e.g. 1.0 mm). This enables results from different sources, which have been measured on the two scales, to be compared.     

基于因子和聚类分析的保护性耕作土壤质量评价研究

基于长期定位试验,选择12项反映土壤质量特性的定量因子作为评价指标,采用因子分析对不同耕作模式的土壤质量进行综合评价,并运用欧氏距离最短法对其进行聚类分析。12项理化及生物属性指标归纳为5个公因子:保肥供肥因子、有机质因子、容重因子、磷素因子、酶活性因子。因子得分的结果表明:不同耕作模式的5个公因子优势差异明显。相比较而言传统耕作的土壤质量综合得分最低,说明在研究区保护性耕作模式条件下土壤在物理、化学、生物学性质方面都有所改善,土壤质量有所提高。土壤质量综合得分最高的前3种处理为隔年深松(NS2)、秸秆覆盖联合浅松、旋耕(SR2)、连年深松(NS3),说明深松、旋耕及秸秆还田与旋耕技术联合作业在改善土壤结构和培肥土壤方面优势更突出。聚类分析结果表明,同一耕作措施的不同模式土壤质量差异较小,说明在本研究试验条件下,耕作措施是影响土壤质量的关键因素。     

Field assessment of soil structural quality – a development of the Peerlkamp test

Increased awareness of the role of soil structure in defining the physical fertility or quality of soil has led to the need for a simple assessment relevant to the environmental and economic sustainability of soil productivity. A test is required that is usable by farmer, consultant and researcher alike. Here an assessment of soil structure quality (Sq) is described which is based on a visual key linked to criteria chosen to be as objective as possible. The influences of operator, tillage and crop type on Sq value were tested. The test takes 5–15 min per location and enough replicates were obtained for statistical comparison of data sets. The assessments of individual operators were influenced to an extent by differences between fields, making the use of multiple operators desirable. Differences in soil management were revealed by the test and related to differences in soil physical properties (bulk density, penetration resistance and porosity) and crop growth. Indicative thresholds of soil management are suggested. The assessment should be viewed as complementary to conventional laboratory assessments of soil structure. Visual soil structure assessment can indicate to the soil scientist where to sample and what soil measurements are likely to be worthwhile.     

Effects of soil water content during primary tillage – laser measurements of soil surface changes

Soil water content during tillage can have a large impact on soil properties and tillage outcome. Measurement of soil relief in relation to fixed elevation points provides a non-destructive method of monitoring loosening/compacting processes during the year. The main objective of this study was to determine the effect of soil water content during primary tillage on soil physical properties.

The treatments included mouldboard and chisel ploughing of a clay soil on three occasions in the autumn, with gradually increasing water content (0.76, 0.91 and 1.01 × plastic limit). Soil surface height was measured by laser within a 0.64 m² area from fixed steel plates after each tillage occasion, and before and after seedbed preparation in the following spring. The measurements of surface height were compared with measurements of other soil physical properties, such as bulk density, saturated hydraulic conductivity and seedbed properties.

Tillage at the lowest water content (0.76 × plastic limit) produced the greatest proportion of small aggregates, and generally the most favourable soil conditions for crop growth. Soil loosening, as measured by increase in soil height during primary tillage, was highest for mouldboard ploughing and for tillage at the lowest water content. Differences between tillage treatments decreased with time, but were still significant after sowing in the spring. Natural consolidation during winter was smaller than the compaction during seedbed preparation in the spring. No significant differences in bulk density were found between treatments, and thus soil surface height was a more sensitive parameter than bulk density determined by core sampling to detect differences between treatments.

Late tillage under wet conditions caused a greater roughness of the soil surface and the seedbed base, which was also found in the traditional seedbed investigation. The effect of tillage time on seedbed properties also resulted in a lower number of emerged plants in later tillage treatments.

The laser measurements were effective for studying changes in soil structure over time. The results emphasize the need to determine changes in soil physical properties for different tillage systems over time in order to model soil processes.     

Spatial variability of short-term effect of tillage on soil penetration resistance

The effect of tillage on soil properties varies within field due to spatial variability of soils. Mapping changes of soil penetration resistance (PR) would be useful to understand and assess tillage practices to alleviate soil compaction. The objectives were to model the short-term effect of tillage on PR and its spatial structure, and to delineate homogeneous zones based on soil response in a Typic Argiudoll previously managed under no-till. A grid sampling for PR and soil water content (SWC) were performed before and after chiselling. Spatial analysis was performed on the effect of tillage on PR data by 10 cm layers and homogeneous zones were delineated by k-means cluster analysis. The effect of tillage was ?0.33 MPa in 10–20 and 20–30 cm layer. No differences of PR were found at 0–10 cm. Short range (5–7 m) spatial structure on the horizontal plane was observed in all layers. Only 45% of the field showed a marked effect of tillage on PR. Mapping the effect of tillage on PR would be a useful approach for evaluating the global and local response of soil to tillage, as well as for delineating of areas within field for site-specific tillage practices.     

Effects of tillage and management practices on soil crust morphology under a Mediterranean environment

Soil crust formation can be affected by soil tillage. Alternative soil conservation practices consisting of reduced tillage were tested against traditional tillage, which involves mechanical weeding by frequent ploughing in rainfed vineyard soils in Catalonia, Spain. After 2 years of the experiment (1994–1996), thin sections of the surface crusts were studied to evaluate the effects of the soil management treatments on crust morphology and genesis, using micromorphological observations and pore characterisation with image analysis. Reduced tillage caused thicker and more complex crusts consisting of layers with different degrees of sorting and pore types, compared to traditional tillage. Total porosity of crusts did not differ from that of non-crusted areas, but pores in crusts were less interconnected, more horizontally distributed and more elongated than in the underlying non-crusted material. The soil type, especially structure and texture, affected crust morphology and played an important role in the process of crusting. The results show that reduced tillage may be limited as an alternative management practice when used to reduce crust formation in Mediterranean conditions, due to the difficulty to establish an effective groundcover.     

Effects of autumn tillage and residue management on soil respiration in a long‐term field experiment in Sweden

Several previous field studies in temperate regions have shown decreased soil respiration after conventional tillage compared with reduced or no‐tillage treatments. Whether this decrease is due to differences in plant residue distribution or changes in soil structure following tillage remains an open question. This study investigated (1) the effects of residue management and incorporation depth on soil respiration and (2) biological activity in different post‐tillage aggregates representing the actual size and distribution of aggregates observed in the tilled layer. The study was conducted within a long‐term tillage experiment on a clay soil (Eutric Cambisol) in Uppsala, Sweden. After 38 y, four replicate plots in two long‐term treatments (moldboard plowing (MP) and shallow tillage (ST)) were split into three subplots. These were then used for a short‐term trial in which crop residues were either removed, left on the surface or incorporated to about 6 cm depth (ST) or at 20 cm depth (MP). Soil respiration, soil temperature, and water content were monitored during a 10‐d period after tillage treatment. Respiration from aggregates of different sizes produced by ST and MP was also measured at constant water potential and temperature in the laboratory. The results showed that MP decreased short‐term soil respiration compared with ST or no tillage. Small aggregates (< 16 mm) were biologically most active, irrespective of tillage method, but due to their low proportion of total soil mass they contributed < 1.5% to total respiration from the tilled layer. Differences in respiration between tillage treatments were found to be attributable to indirect effects on soil moisture and temperature profiles and the depth distribution of crop residues, rather than to physical disturbance of the soil.     

Microbial community response to transition from conventional to conservation tillage in cotton fields

In the southeastern United States, conservation tillage techniques are used to conserve soil nutrients and structure, providing habitat and substrate for biota, which are largely responsible for the mineralization of nutrients in the soil. A deterrent for growers considering the transition to conservation tillage is the delay in soil response (e.g. increased soil carbon, efficient nutrient cycling, impacts on yield) associated with the equilibration of the soil food web. The objective of this study was to determine if the microbial community composition and biomass changed with transition to conservation tillage. Soils sampled from five sites, representing a chronosequence of conservation tillage (from conventionally tilled to 30 year no-till), were collected for fatty acid analysis. Microbial communities were significantly different among sites. Fungi, characterized by 18:2ω6, 18:1ω9, and 18:3ω6c fatty acids, were typically lowest in the conventionally tilled soil, probably due to repeated disruption of the fungal hyphae associated with tillage. In all soils, soil nutrient concentrations, moisture and microarthropod abundance were correlated with microbial structure. Plots in conservation tillage were significantly different from the conventionally tilled plots, but did not exhibit a clear linear pattern across the chronosequence. This evidence that belowground food webs can respond quickly to a cessation in tillage suggests that the delay in soil response may be due more to the time required to build organic matter than to a slow response by the biota.     

苏南地区水稻土的合理耕作的研究

苏南地区传统的土壤耕作要求水稻移栽前耕层土壤“上有泥糊、下有团块”,认为泥糊有利于土壤的养分释放,团块有利于土壤通气^[2];而对于秋耕,力求达到耕层土碎、田面平整。为此,必须耕耙配套,因而每年化费的劳动和能量很大。七十年代以来,由于大面积发展双三制,耕作次数增多和溃水时间延长,难以实现晒堡,农民普遍反映土壤发僵,通气性变坏^[1,4,7],碎土更加困难。为了摸清传统土壤耕作制中存在的问题,探索合理的土壤耕作制,我们于1978-1979年在无锡等地进行了不同整地方法的田间试验,并就出现的问题进行了盆栽对比研究。     

免耕对稻油轮作系统土壤结构的影响

为探明免耕对稻油轮作系统土壤结构的影响,基于湖南省洞庭湖区4a的耕作试验(2016—2019),采用X射线CT扫描技术和常规土壤物理分析方法,研究了旋耕和免耕对水稻土0～25 cm土层土壤结构的影响。与旋耕相比,免耕处理对0～5 cm土层的土壤容重和土壤有机碳无显著影响,但免耕处理显著提高了0～10 cm土层>2 mm团聚体的含量和团聚体稳定性。不同耕作方式改变了土壤大孔隙度和孔隙大小分布,与旋耕处理相比,免耕处理增加了0～5和5～10 cm土层各个孔径范围内(>25μm)的大孔隙度,其中0～5 cm土层300～500μm孔径的大孔隙显著增加了70.5%,5～10 cm土层25～300和300～500μm孔径的大孔隙分别增加了82.8%和167.2%(P<0.05)。研究表明,稻油轮作系统免耕有利于提高表层土壤团聚体稳定性和大孔隙度,改善水稻土结构状况。     

The structure of two alluvial soils in Italy after 10 years of conventional and minimum tillage

Micro and macroporosity, pore shape and size distribution, aggregate stability, saturated hydraulic conductivity and crop yield were analysed in alluvial silty loam (Fluventic Eutrochrept) and clay soils (Vertic Eutrochrept) following long-term minimum and conventional tillage. The soil structure attributes were evaluated by characterizing porosity by means of image analysis of soil thin sections prepared from undisturbed soil samples.

The interaggregate microporosity, measured by mercury intrusion porosimetry, increased in the minimally tilled soils, with a particular increase in the storage pores (0.5–50 μm). The amount of elongated transmission pores (50–500 μm) also increased in the minimally tilled soils. The resulting soil structure was more open and more homogeneous, thus allowing better water movement, as confirmed by the greater hydraulic conductivity of the minimally tilled soils. The aggregate stability was less in the conventionally tilled soils and this resulted in a greater tendency to form surface crusts and compacted structure, compared with the minimally tilled soils. The latter tillage practice seemed to maintain, in the long-term, better soil structure conditions and, therefore, maintain favourable conditions for plant growth. In the silt loam, the crop yield did not differ significantly between the two tillage systems, while in the clay soil it decreased in the minimum tilled soil because of problems of seed bed preparation at the higher surface layer water content.     

Untersuchungen zum Bodenlufthaushalt in einem Bodenbearbeitungsversuch. 2. Gasdiffusionskoeffizienten als Strukturmaße für Böden

Investigation of the soil gas regime in a tillage experiment: 2. Apparent diffusion coefficients as a measure of soil structure In a soil tillage experiment with nursery stock on three different soils the apparent diffusion coefficients for CO₂ were measured using soil cores of different depths at different times. Not-tilled, herbicide treated plots were compared with rototilled plots. The relationship between the relative apparent diffusion coefficient and the air content may be described by an exponential regression function D_s/D_a = 0.0085 · e^6.8E_L, if all measurements are taken into the calculation. By dividing into different soil textures different regressions are obtained for the three studied soils: a sand, a silt and a clay loam. In many cases it is possible to show by the changing D_s(E_L) regression changes of the soil structure with depth or as a result of tillage. In all these cases the soil of the not tilled plots turns out to be better structurized than that of the tilled ones, demonstrated by higher D_s-values at equal E_L. The interpretation of the differences is being tried with the aid of soil pore tortuousity and continuity. Finally the measured D_s(E_L) relationships are applied to characterize the soil gas regime for two seasons, using CO₂ concentration profiles of the soil air on a day in summer and fall, respectively. It is shown, that CO₂ production reaches farther down in summer than in fall.     

Acquisition and analysis of three-component digital images of soil pore structure. II. Application to seed beds in a fallow management trial

Seed beds of a tillage and fallow management trial were examined using the techniques of field impregnation and image analysis described in Part I of this paper. The trial was situated near Warwick on the Darling Downs, Queensland, Australia on a self-mulching black earth soil with wheat as the test crop. The effects of both frequency of tillage operations and of burning vs. retention of stubble on the pore structure are examined. The only effect detected in the top 50 mm was due to stubble burning. The tilth layer was finer in the cultivated treatment. Cultivation was seen to reduce the connectivity of pore space. This effect was greatest when combined with burning of stubble. The image analysis results were found to be consistent with other data generated from the same trial.     

Reassessment of tillage erosion rates by manual tillage on steep slopes in northern Thailand

Changing land-use practices in northern Thailand have increased tillage intensity. This study re-assesses the rate of tillage erosion by manual hoeing on steep slopes (17–82%) in northern Thailand. Previously collected soil translocation data during an on-farm tillage erosion experiment and additionally collected data during an on-farm tillage erosion survey have been analysed whereby a new calculation method (i.e. trapezoid tillage step) has been used. A comparison with previously collected data indicates that the trapezoid tillage step method and the tracer method are the most reliable methods to assess downslope translocation by manual tillage. Based on newly acquired understanding of the processes involved, soil fluxes by tillage erosion are quantified by linear functions for different slope gradient classes rather than one single diffusion-type equation for the whole slope range. For slope gradients smaller than 3%, soil fluxes are close to zero as farmers do not have a preferred tillage direction. For slope gradients between 3% and 70%, soil is tilled only in the downslope direction and soil fluxes range between 16 and 67 kg m⁻¹ tillage pass⁻¹. On slopes with gradients in excess of 70%, the angle of repose for soil clods is often exceeded resulting in a sliding down of the complete tilled top layer. These data are used to assess the soil flux for complete cropping cycles for the most dominant cropping systems in the highlands of northern Thailand: i.e. upland rice, maize, (soy) beans, cabbage and ginger. The on-site effects of tillage erosion will be very pronounced if parcels are short with respect to their slope length, cultivated for upland rice or cabbage, or when weed pressure is high. Tillage erosion results in a tillage step with low soil fertility and low infiltration capacity. Solutions to reduce tillage erosion intensity depend on the degree that tillage intensity can be reduced. This might happen by an improved weed management or by changing landuse to perrenial cropping. Other strategies are concentrating nutrients on the truncated hillslope sections and retaining soil on the field by vegetative buffers.