GrassVESS: a modification of the visual evaluation of soil structure method for grasslands

Visual evaluation of soil structure (VESS ) is used for assessing arable management impact on soil quality. When used on pastures, operators have identified limitations because VESS does not consider a surface root‐mat typical of managed grassland. The structure of the root‐mat may be indicative of nutrient use efficiency, pollution potential and subsurface compaction. The objectives of this research were to develop GrassVESS for grassland soil management, to compare it with VESS and quantitative physical indicators and to assess its utility for soil management. GrassVESS maintained the methodological strengths of VESS , but uses a flow chart, grassland images and a new root‐mat score. A focus group found GrassVESS to be quicker, dealt better with technical information and made root‐mat evaluation easier. The range of structural quality scores assigned by the focus group for a site was less for GrassVESS than VESS , suggesting the procedure is more reproducible, thus suitable for use by a range of stakeholders. GrassVESS was also deployed at 30 grassland sites across Ireland. Results indicated that GrassVESS generated the same overall diagnoses as VESS , but the GrassVESS root‐mat structural quality score was better related to bulk density, total porosity at 5–10 cm and a visual estimation of damaged sward area. It was concluded that GrassVESS has improved the VESS method for the specific assessment of grassland soil structural quality and could be used in real‐time farm management decision support.     

Evaluating the long-term effects of tillage systems on soil structural quality using visual assessment and classical methods

Current agricultural practices and their impacts on the sustainability of crop production can be evaluated by simple and reliable soil structure assessment tools. The study was conducted to determine the effects of long-term (2006–2017) tillage systems on structural quality of a clayey soil using the visual evaluation of soil structure (VESS) and classical field and laboratory measurements. A field experiment with seven tillage systems, representing both traditional and conservation tillage methods, was conducted on a clayey soil in the Cukurova region, Turkey. Soil samples from 0–10, 10–20 and 20–25 cm depths were analysed for mean weight diameter (MWD), porosity and organic carbon. Penetration resistance (PR) was determined in each treatment plot. The VESS scores (<2) of upper 0–5 cm indicated a good structural quality for all tillage systems. The VESS scores were positively related to PR and MWD and negatively to macroporosity (MaP) and total porosity. In reduced and no-till systems, poorer soil structures were observed in subsurface layers where firm platy and angular blocky structures were defined. Mean VESS score (3.29) in 20–25 cm depth where PR was 3.01 MPa under no-till indicated a deterioration of soil structural quality; thus, immediate physical interventions would be needed. Lower VESS scores and PR values under strategic tillage which was created by ploughing half of no-till plots in November 2015 indicated successful correction of compaction caused by long-term no-till. The results suggest that the VESS approach is sensitive and useful in distinguishing compacted layers within the topsoil.     

Visual Evaluation of Soil Structure Under Grassland management

Twenty sites representing the typical range of grass‐based beef and dairy production management intensity in Ireland were used to assess soil structural quality with the Visual Evaluation of Soil Structure (VESS) method combined with laboratory analysis. The results showed that VESS was suitable for assessing soil structural quality for grassland productivity. According to the threshold values proposed by Ball [Soil Use and Management (2007), 23 , 329–337] for management intervention, all fields except one in this study were between Sq 1 and Sq 3, indicating that the typical range of management intensity does not cause undue soil damage and can be regarded as sustainable for soil structure. There was an indication that as intensification increases, temperate maritime grassland soils showed signs of degradation with respect to soil structure for maintaining grass productivity. While reseeding might solve some problems, it causes others due to the release of soil carbon. This raises the prospect that ‘sustainable intensification’ of livestock production may be limited by the health of the soil resource that supports it. Significant negative correlations between Sq and soil C content (P < 0.01) and between Sq and soil N content (P < 0.05) were observed, indicating a close relationship between soil structure and soil carbon and nitrogen.     

Effect of rain on the macroporosity at the soil surface

Rain falling on soil causes slaking, mechanical disruption of aggregates and compaction. Too few data exist to predict the changes likely to occur in particular soil, landscape and management conditions. Experiments with simulated rain were set up to study and to model mathematically the changes of the pore system within the surface layer of a soil when rain was applied on a field cropped with maize. Macroporosity, pore‐size and pore‐shape distributions, and the pore volume were measured by image analysis of thin sections and the fractal dimensions of the pore surface roughness were estimated. The general trends of changes in porosity indicated the presence of two different sets of processes at the surface (0–3 cm) and in the layer immediately underneath (3–6 cm). In both layers most of the variation in macroporosity was due to a loss of elongated porosity. A theoretical approach recently developed to link rain and erosion to sealing properties was extended to describing the effect of rain on the elongated porosity and the pore volume fractal dimension in these two layers. The resulting set of equations describe in detail the evolution of soil porosity near the soil surface. Our approach could be useful when modelling the effects of sealing processes in soil erosion.     

Water retention characteristics of soils with double porosity

A soil with double porosity is modelled as a collection of aggregated particles, in which a single aggregate is made up of discrete particles bonded together. Separate fractal distributions for pore sizes around and within aggregates are defined. The particle size distribution of the double porosity soil is also modelled using a fractal distribution, which may have a fractal dimension very different to those defining the pore sizes. The surface areas of the particles and the pores within the aggregates are assumed to be equal, enabling an expression linking two fractal dimensions to be defined. It is necessary to introduce ratios between maximum and minimum particle and pore sizes into the expression. A theoretical soil‐water characteristic curve is then derived for a double porosity soil. The curve, and the underlying assumptions regarding the distributions of pore and particle sizes, showed good agreement with experimental data for a range of soils having double porosity. A discontinuity is observed in the soil‐water characteristic curve at a second air entry value related to the maximum pore size within the aggregates, a feature also observed in experimentally obtained soil‐water characteristic curves for double porosity soils.     

Morphological characterisation of weathered earthworm casts by 2D-image analysis

Earthworm casts weathered by rainfall are difficult to differentiate from surrounding soil aggregates. We tested the hypothesis that morphological characterisation of soil aggregates by 2D-image analysis helps to perform this differentiation. Compact surface casts produced by Amynthas khami and surrounding aggregates lacking visible signs of biological activity (control) were left to disaggregate by natural rainfall and were separated into five size classes (10–5, 5–2, 2–0.5, 0.5–0.25 and <0.25?mm). The external shape and pore-space characteristics of aggregates were measured by image analysis. Casts >2?mm were characterised by less surface roughness and similar round shape than control aggregates. However, casts and control aggregates <2?mm had a similar external shape. The structural porosity of casts >0.25?mm was lower than that of control aggregates, whereas their textural porosity was similar. Therefore, this study demonstrates that measuring the porosity of soil aggregates by 2D-image analysis is a better indicator of earthworm-aggregate origin than external shapes.     

Application of the photographic method to determine the aggregate porosity

Existing methods to study the aggregate porosity are examined. The need to develop new methods is shown. The theoretical basis for modeling soil aggregates of irregular shape is presented. The methodology of studying soil aggregate porosity is explained in detail, and the necessary number of replicates of the experiment is suggested. The applicability of the photographic method is confirmed for different soils. The field of application of data on the soil aggregate porosity as obtained by the method of image analysis is specified.     

Soil organic carbon,nitrogen, and phosphorus distribution in stable aggregates of an Ultisol under contrasting land use and management history

Different land‐use affects the organization of mineral soil particles and soil organic components into aggregates and the consequent arrangement of the aggregates will influence essential ecosystem functions. We investigated a continuous rubber plantation (forested), land fallowed for 10 y (fallow), 10‐y continuous arable cropping land and cropped land with top soil removed (TSR) for concentrations of C, N, and P in bulk soil and dry aggregates. Results showed that a high level of soil disturbance decreased the proportion of surface (0–15 cm) soil aggregate stability (low mean weight diameter) in TSR by 149% and arable cropping by 125% compared with the forested. Aggregate associated SOC was higher in aggregate‐size fractions of forested land‐use when compared with that in 10‐y fallow, continuous arable cropping, and TSR. For aggregate associated N, fallow and forested land‐use types concentrated higher proportion across aggregate sizes than the arable cropping and TSR. Macro aggregate fractions generally contained higher concentrations of C, N, and P compared with the micro‐aggregates. Water transmission indicators like total porosity and saturated hydraulic conductivity recorded higher values with forested and fallow land‐use than the others. We can thus conclude that long‐term soil disturbance due to cultivation and removal of top soil reduces the accumulation of soil C, N, and P in bulk soil and decreases water transmission properties. On the other hand, aggregate‐associated C, N and P accumulations are dependent on the level of soil surface disturbance and aggregate sizes.     

Aggregate breakdown during tillage in a Mediterranean loamy soil

Long-term tillage negatively affects soil aggregation, but little is known about the short-term effects of tillage. We investigated the effects of intensive tillage (moldboard plowing) and conservation tillage (chisel plowing) on aggregate breakage during tillage in a long-term study located in the semiarid Ebro river valley (NE Spain). The type of tillage resulted in different soil aggregate distributions. In the 0–5-cm and 5–10-cm soil layers, chisel plowing decreased dry mean weight diameter (DMWD) 29% and 35%, respectively, while moldboard plowing decreased DMWD by only 2% and 16%, respectively. The decrease in DMWD was mainly due to breaking of large aggregates ranging (2–8 mm) into small aggregates (<0.5 mm). Tillage method had no effect on water stability of 1–2 mm aggregates. The differences in DMWD demonstrate that the choice of the tillage implement can be a key factor in improving soil management and productivity. The surprising result that aggregate breakdown was greater with chisel than moldboard plowing needs further research to determine the mechanisms controlling aggregate breaking during tillage.     

用显微CT研究不同植被恢复模式的土壤团聚体微结构特征

为了更好了解不同植被恢复模式对土壤团聚体微结构的影响,该研究采用显微CT技术扫描3~5 mm土壤团聚体,获取了3.25μm分辨率的二维图像,并应用数字图像处理软件对团聚体孔隙结构进行三维重建,定量研究了黄土丘陵区不同植被恢复模式下(自然草地、人工灌木和坡耕地)土壤团聚体微结构特征。结果表明,两种植被恢复模式均显著提高了土壤有机碳含量和团聚体水稳性(P0.05),降低了土壤容重。与坡耕地处理相比,自然草地土壤团聚体总孔隙度、大孔隙度(100μm)、瘦长型孔隙度分别增加了20%、23%和24%,而分形维数和连通性指数欧拉特征值分别降低了2%和75%,且各指标二者间差异均显著(P0.05)。人工灌木土壤团聚体的上述各项孔隙参数均优于自然草地(较坡耕地分别增加了70%、88%和43%以及降低了4%和92%),且除欧拉特征值外,差异均显著(P0.05)。分形维数和连通性对土壤结构变化的响应相当敏感,可作为该地区植被恢复过程中土壤质量评价的指标,研究结果可为黄土高原土壤质量评价提供科学参考。     

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.     

岩溶坡地不同利用类型土壤入渗性能及其影响因素

为了探讨岩溶坡地不同土地利用类型土壤入渗性能差异及其影响因素,该文利用环刀法测定了不同利用类型石灰岩土壤的入渗过程曲线,并分析了孔隙状况、颗粒组成和土壤结构等对入渗的影响。结果表明：土地利用类型对岩溶坡地土壤入渗性能影响较大,初始入渗速率和稳定入渗速率均表现为灌丛＞果园＞草地＞旱地。灌丛地表下层（＞15～30 cm）平均稳定入渗速率8.11 mm/min,最小值4.22 mm/min;旱地地表下层平均稳定入渗速率0.46 mm/min,最小值仅0.13 mm/min。旱地表层以下存在显著的入渗阻滞层。岩溶坡地土壤入渗性能与有机质、水稳性团聚体和孔隙度有显著相关性。非毛管孔隙在入渗初期的作用大于后期,＞0.25 mm水稳性团聚体含量是影响稳定入渗速率的重要因素。该文为进一步研究岩溶坡地旱涝灾害、水土保持和水资源开发利用等提供了理论依据。     

The effect of dairy sewage sludge amendment on repellency and hydraulic conductivity of soil aggregates from two depths of Eutric Cambisol

Appropriate management of sewage sludge is an important worldwide issue due to the still growing amount of wastewaters. In the study we examined to what extent the addition of dairy sewage sludge compared with mineral fertilization affects porosity, repellency index, and hydraulic conductivity of variously sized aggregates from two soil depths of Eutric Cambisol derived from loess: 5–15 cm and 25–35 cm. The repellency index was calculated as a ratio of ethanol and water sorptivity. Data on water and ethanol sorptivities of initially air‐dry soil aggregate fractions were obtained from steady state flow measurements using an infiltration device. Hydraulic conductivity was determined by measuring water infiltration at five pressure heads: –8, –6, –4, –2, and 0 cm of water column with the same device as for sorptivity determination. Addition of sewage sludge to the soil decreased the soil repellency index by an average of 27% in topsoil and 32% in subsoil for both aggregate sizes, respectively, and increased hydraulic conductivity about four times in both layers. Smaller aggregates (15–20 mm diameter) from soil amended with sewage sludge, in comparison with larger ones (30–35 mm diameter), had a higher repellency index by 36 and 24% in topsoil and subsoil, respectively. As for aggregates from soil with mineral fertilization, those differences were smaller and equal to 15% in subsoil, in topsoil smaller aggregates even had slightly lower repellency index (by 5%). Aggregates taken from the upper soil layer were more water repellent and had smaller hydraulic conductivity than those taken from subsoil, regardless of soil treatment and aggregate size.     

冻融循环对黑土团聚体稳定性与微结构特征的影响

冻融循环作用下的土壤结构变化被认为是融雪期黑土坡面土壤侵蚀加剧的主要原因之一,土壤团聚体稳定性与团聚体微结构是影响土壤可蚀性的关键因子.基于控制条件土壤冻融模拟试验,采用湿筛法、扫描电子显微技术(SEM)和Image-Pro Plus(IPP)图像分析处理相结合的方法,分析了冻融循环过程中黑土团聚体微结构的动态变化特征...     

土壤结构的性态研究

提高土壤肥力的目的主要在于充分发挥土壤潜在能力,保证农作物的高额稳产.为了达到这个目的,必须定向控制土壤的变化,改善土壤状况.土壤肥力是各种土壤性质的综合表现,并随着环境和时间而不断变化.要彻底了解土壤肥力,不仅要明悉土壤供应肥、水的容量和供应的快慢及持续时间,还要考虑肥、水的协调和植物根系的生活条件,这就是我们所称的肥力基础(简称肥基).     

耕层构造的土壤结构质量-径级数字图像分析

为了探讨以土壤结构体为单元的耕层构造定量方法,该文利用犁耕生成的土壤结构体2D图像计算其质量-径级分布。分别以30°、45°、60°及90°拍摄获取土壤结构体的数字图像,计算土壤结构体各径级区间的几何指标,拟合质量-径级分布模型。结果表明土壤结构体的棱角性和形状指数随径级增大而增加,但矩形度随之减小;以60°拍摄所得的土壤结构体质量-投影面积关系的拟合精度最高,各粒径区间R2均不低于0.89;数字图像筛分与手工测量所得的土壤结构体质量-径级分布无显著差异(P0.05),表明数字图像筛分是从2D投影面信息获取土壤结构体质量-径级分布的准确方法;相对于Weibull和Rosin-Rammler模型,用Gaudin-Schuhmann模型拟合获得的土壤结构体质量-径级分布效果较优,用该模型拟合数字图像筛分所得的土壤结构体质量-径级分布,R2为0.98;相对于干筛法,数字图像筛分方法的划分的径级区间更精细,所得的模型拟合精度更高。     

黄土高原丘陵沟壑区经济作物欧李的水土保持功能

[目的]研究经济作物欧李在黄土高原丘陵沟壑区的水土保持功能,为当地推广欧李种植提供理论支撑。[方法]以山西省吕梁市柳林县4类试样样地为对象,对欧李种植区土壤持水性、团聚体水稳定性及抗蚀性进行研究。[结果](1)欧李种植区土壤容重明显低于其他样地土壤,其中阳坡欧李Ⅲ号区土壤容重最低,表层和亚表层分别为0.954,1.163g/cm3,容重与总孔隙度、毛管孔隙度呈极显著负相关。(2)欧李在黄土高原丘陵沟壑区适应性极强,通过种植可以显著改善土壤肥力。(3)欧李样地土壤0.25mm风干及水稳性团聚体、土壤团聚体平均重量直径及团聚体水稳性指数均远高于该地区传统水土保持植物样地和撂荒地样地的土壤,并且团聚体破坏率最低。(4)欧李样地土壤0—40cm土层平均可蚀性因子K值最低,对表层及亚表层土壤保护效果更好。(5)K值与黏粒和有机质含量呈极显著负相关,与粉粒含量呈极显著正相关,土壤质地决定土壤抗蚀性能。[结论]欧李在黄土高原丘陵沟壑区具有很好的适应性,不仅可以增加农民收入,更对提高当地水土保持能力,改善生态环境具有重要意义。     

PAM-atta复合保水剂对土壤物理性质的影响

在研制开发出耐盐型丙烯酰胺/凹凸棒黏土复合保水剂(PAM-atta)的基础上,研究了该复合保水剂对土壤物理性质的影响。结果表明:PAM-atta复合保水剂可显著提高土壤含水量、>0.25mm团聚体含量、孔隙度以及阳离子交换量,降低土壤体积质量(容重)。同时PAM-atta复合保水剂粒径越小,对土壤体积质量、团聚体等的作用效果也越明显。与CK相比,施用120目的保水剂可提高土壤中>0.25mm团聚体含量达13.3%~16.2%。     

Simple Modification of the Clod Method for Determining Bulk Density of Very Gravelly Soils

Abstract

The accuracy of the clod method in determining fine‐earth bulk density in very gravelly soils can be affected by the difficulty of fine‐earth separation from both coarse fragments and the coating substance. A modification of the paraffin‐coated clod method is presented that accurately determines fine‐earth bulk density of very gravelly soils. The modification involves washing the paraffin‐coated clod in boiling water to separate paraffin from gravel and hardened soil aggregates. Samples were analyzed with an existing gravel correction method, herein referred to as the hand removal method (HRM), and the proposed modification, which is named the gravel washing method (GWM). Bulk density means for HRM and GWM were 1.29 and 1.41 g cm^?3, respectively. This trend of higher bulk densities for GWM was consistent across pedons sampled in the study and was attributed to its ability to completely remove wax from gravels and hardened soil aggregates, effectively separating the fine‐earth fraction.     

阿基米德螺线型破茬开沟和切拨防堵装置的设计与试验

针对东北保护性耕作区玉米垄作农业技术对研发免耕播种机的要求,该文以阿基米德螺线为基础,分析了缺口圆盘刀破茬性能和理想种床对破茬刀的技术要求,进行了阿基米德螺线型缺口圆盘破茬刀的结构优化以及最优参数的优选,研制了破茬开沟和切拨防堵装置。田间试验表明,破茬开沟装置能开出"V"形沟,2片螺线型缺口圆盘刀直径为350 mm、入土深度为40 mm时,播种开沟宽度为28 mm;切拨防堵装置单片圆盘破茬装置质量为113 kg、破茬深度为70~100 mm时,开沟宽度为40~50 mm,清垄部件清垄宽度为210 mm,均达到了农业技术要求。同时,确定提高破茬率切拨防堵装置的最佳工作参数:机器前进速度为2.22 m/s,配质量为113 kg,破茬圆盘刀入土深度为7.50 cm;得出各因素对破茬率影响的主次顺序为机器配质量机器前进速度入土深度。该研究为高留茬模式和高留茬碎杆覆盖模式的保护性耕作地区的免耕播种作业提供了参考。