Traffic Compaction Research Articles

Soil, climate, time and site factors as drivers of soil structure evolution in agricultural soils from a temperate-boreal region

The evolution of soil structure in agricultural soils is driven by natural and anthropogenic factors including inherent soil properties, climate and soil management interventions, all acting at different spatial and temporal scales. Although the causal relationships between soil structure and these individual factors are increasingly understood, their relative importance and complex interactive effects on soil structure have so far not been investigated across a geo-climatic region.Here we present the first attempt to identify the relative importance of factors that drive the evolution of soil structure in agricultural soils as well as their direction of effect with a focus on the temperate-boreal zone. This was done using a random forest (RF) approach including soil, climate, time, and site factors as covariates. Relative entropy, as quantified by the Kullback-Leibler (KL) divergence, was used as a quantitative index of soil structure, which is derived from the particle-size distribution and soil water retention data, and integrates the effects of soil structure on pores from the micrometre-scale to large macropores. Our dataset includes 431 intact topsoil and subsoil samples from 89 agricultural sites across Sweden and Norway, which were sampled between 1953 and 2017. The relative importance of covariates for the evolution of soil structure was identified and their non-linear and non-monotonic effects on the KL divergence were investigated through partial dependence analysis. To reveal any differences between topsoils (0–30 cm; n = 174) and subsoils (30–100 cm; n = 257), the same analysis was repeated separately on these two subsets.The covariates were able to explain on average more than 50% of the variation in KL divergence for all soil samples and when only subsoil samples were included. However, the predictions were poorer for topsoil samples (≈ 35%), underlining the complex dynamics of soil structure in agricultural topsoils. Parent material was the most important predictor for the KL divergence, followed by clay content for all soil samples and sampling year for only subsoil samples. Mean annual air temperature ranked third and annual precipitation ranked fourth for subsoil samples. However, it remains unclear whether the effects of climate factors are direct (e.g., freezing and thawing, wetting and drying, rainfall impact) or indirectly expressed through interactions with soil management. The partial dependence analysis revealed a soil organic carbon threshold of around 3% below which soil structure starts to deteriorate. Besides this, our results suggest that subsoil structure in the agricultural land of Sweden deteriorated steadily during the 1950′s to 1970′s, which we attribute to traffic compaction as a consequence of agricultural intensification. We discuss our findings in the light of data bias, laboratory methods and multicollinearity and conclude that the approach followed here gave valuable insights into the drivers of soil structure evolution in agricultural soils of the temperate-boreal zone. Theses insights will be of use to inform soil management interventions that address soil structure or soil properties and functions related to it.

Thirteen‐year stover harvest and tillage effects on soil compaction in Iowa

AbstractCorn (Zea mays L.) stover is an abundant biomass source with multiple end‐uses including cellulosic biofuel production. However, stover removal may increase soil compaction by reducing organic matter inputs and increasing vehicle loads during harvest. While numerous studies have reported stover removal impacts on soil physical quality, few have assessed the role played by traffic compaction. Our objective was to quantify subsurface soil compaction after 13 years of chisel plow versus no‐till management and no, moderate (3.5 ± 1.1 Mg ha−1 year−1), or high (5.0 ± 1.7 Mg ha−1 year−1) stover harvest rates. Penetration resistance was measured in most‐ and least‐trafficked interrow spaces. Chisel plowed plots with moderate and high levels of stover removal had higher penetration resistance in trafficked areas relative to least‐trafficked areas, whereas there was no evidence of traffic compaction when stover was retained. Traffic compaction did not negatively impact yields, which were greater with high levels of stover removal compared to no removal. The no‐till practice led to very small increases in penetration resistance with wheel traffic and had no evidence of increased compaction with residue removal. This lack of traffic compaction indicated soils under no‐till practice have a higher load‐bearing capacity than soils under chisel plow practice. Overall, there were no yield‐limiting effects of tillage practice or stover removal, and no evidence of soil compaction below the plow layer, suggesting stover removal with both tillage practices can be effectively employed without detrimental effects on plant or soil health.

Soil and crop management practices and the water regulation functions of soils: a qualitative synthesis of meta-analyses relevant to European agriculture

Abstract. Adopting soil and crop management practices that conserve or enhance soil structure is critical for supporting the sustainable adaptation of agriculture to climate change, as it should help maintain agricultural production in the face of increasing drought or water excess without impairing environmental quality. In this paper, we evaluate the evidence for this assertion by synthesizing the results of 34 published meta-analyses of the effects of such practices on soil physical and hydraulic properties relevant for climate change adaptation in European agriculture. We also review an additional 127 meta-analyses that investigated synergies and trade-offs or help to explain the effects of soil and crop management in terms of the underlying processes and mechanisms. Finally, we identify how responses to alternative soil–crop management systems vary under contrasting agro-environmental conditions across Europe. This information may help practitioners and policymakers to draw context-specific conclusions concerning the efficacy of management practices as climate adaptation tools. Our synthesis demonstrates that organic soil amendments and the adoption of practices that maintain “continuous living cover” result in significant benefits for the water regulation function of soils, mostly arising from the additional carbon inputs to soil and the stimulation of biological processes. These effects are clearly related to improved soil aggregation and enhanced bio-porosity, both of which reduce surface runoff and increase infiltration. One potentially negative consequence of these systems is a reduction in soil water storage and groundwater recharge, which may be problematic in dry climates. Some important synergies are reductions in nitrate leaching to groundwater and greenhouse gas emissions for nonleguminous cover crop systems. The benefits of reducing tillage intensity appear much less clear-cut. Increases in soil bulk density due to traffic compaction are commonly reported. However, biological activity is enhanced under reduced tillage intensity, which should improve soil structure and infiltration capacity and reduce surface runoff and the losses of agro-chemicals to surface water. However, the evidence for these beneficial effects is inconclusive, while significant trade-offs include yield penalties and increases in greenhouse gas emissions and the risks of leaching of pesticides and nitrate. Our synthesis also highlights important knowledge gaps on the effects of management practices on root growth and transpiration. Thus, conclusions related to the impacts of management on the crop water supply and other water regulation functions are necessarily based on inferences derived from proxy variables. Based on these knowledge gaps, we outlined several key avenues for future research on this topic.

Soil degradation after the traffic of a military combat vehicle leopard 1a5br

Heavy vehicle traffic, especially large military combat vehicles, causes soil compaction, which reduces their physical quality and increases their susceptibility to soil erosion. A large contingent of the Brazilian Army conducts combat vehicle training at the Santa Maria Instruction Field (CISM), which has been caused degradation of the ecosystem. The aim of this study was to evaluate the effect of combat vehicle Leopard 1A5BR traffic on soil physical properties in an Abruptic Alisol with military vehicle traffic history. Two types of maneuvers were evaluated: (i) straight traffic with 0, 1 and 3 passes, and (ii) pivoting maneuver with 0, 1 and 2 pivots. Soil morphology, particle size distribution and organic carbon content were analyzed in the 0.00-0.10 and 0.20-0.30 m layers. Bulk density, total porosity, macroporosity, microporosity, saturated soil hydraulic conductivity, penetration resistance and preconsolidation pressure were evaluated in the 0.00-0.04, 0.10-0.14 and 0.20-0.24 m layers. The preconsolidation pressure of the surface layer indicated that the soil surface layer is susceptible to traffic compaction of Leopard 1A5BR. Only one pass (straight traffic) and one pivoting maneuver were sufficient to increase soil penetration resistance and bulk density and reduce the total porosity and macroporosity in the surface layer (0.00-0.04 m).

Residual effects of phosphogypsum rates and machinery traffic on soil attributes and common-bean (Phaseolus vulgaris) yield in a no-tillage system

Phosphogypsum (PG) affects many soil attributes, but its long-term effects on soil structure and physical properties remain unclear. We evaluated the residual effects of PG and induced soil compaction on selected soil chemical and physical attributes, and on common bean (Phaseolus vulgaris) yield. The experiment was initiated on a Typic Hapludox soil using a split-plot design with four replicates. In November (2009), PG at rates of 3, 6, 9, 12 Mg ha−1 was broadcast on the soil surface. In November (2012), traffic compaction was applied to the soil and the treatments were wheel-track (WTR), between wheel tracks (BWT) and no traffic/reference (REF) zones. Compaction was applied with a four-wheel-drive tractor with 2.4 and 3.6 Mg on the front and rear axles, respectively, at field water capacity (FC). Common bean was sown in February (2013) and its yield was assessed at physiological maturity. Forty-two months after application of traffic treatments, the 0.0−0.1 and 0.1−0.2 m soil layers were sampled. Phosphogypsum decreased exchangeable acidity and Al3+ concentrations, and increased pH and Ca2+ in both soil layers, as well as SO42- in the 0.1−0.2 m layer. Despite increasing water-dispersible clay (WDC), PG decreased aggregate tensile strength (TS) at the WTR and BWT zones. Phosphogypsum rates increased organic carbon concentrations in soil aggregates. Machinery traffic increased the values of WDC and TS, but also decreased common bean yield. PG application alleviated the negative impacts of wheel traffic on TS. We conclude that the residual effect of PG can positively affect soil chemical and physical attributes and contribute to alleviate the impacts of machinery traffic.

GPR imaging of traffic compaction effects on soil structures

Spatial and depth variability of soil characteristics greatly influence its optimum utilization and management. Concealing nature of soil subsurface horizons has made the traditional soil investigations which rely on point information less reliable. In this study, an alternative use of ground penetrating radar (GPR)—a near-surface geophysical survey method—was tested to address the shortcomings. The focus of the study was on assessment of characteristics variability of soil layers at a test site and evaluation of effects of compaction caused by machinery traffics on soil. GPR methods utilize electromagnetic energy in the frequency range of 10 MHz and 3.0 GHz. Fourteen profiles GPR data were acquired at the test site-a farmland in Krakow, Poland. Compaction on parts of the soil was induced using tractor movements (simulating traffic effects) at different passes. Data were processed using basic filtering algorithms and attributes computations executed in Reflexw software. Attempt made in the study was on use of GPR geophysical technique for soil assessment. The method allows delineation of the soil horizons which depicts characteristic depth changes and spatial variability within the horizons. Moreover, traffic effects that caused compaction on parts of the soil horizons were discernable from the GPR profile sections. Thus, similar densification like hardpan that may develop in natural setting can be investigated using the method. The results have shown the suitability of the method for quick, noninvasive and continuous soil investigation that may also allow assessment of temporal soil changes via repeated measurement.

A simple method for predicting the hydraulic properties of unsaturated soils with different void ratios

Reliable estimates of the unsaturated soil hydraulic properties are needed in many research and engineering projects. The void ratio or bulk density is an important factor affecting the unsaturated soil hydraulic properties. The bulk density of one soil can change considerably due to the influences of rain, irrigation, and traffic compaction. It remains a difficult task to accurately describe the hydraulic hysteresis of the unsaturated soil with different void ratios or bulk densities. The aim of this study was to evaluate hydraulic hysteresis behavior and permeability of unsaturated soil with different void ratios or bulk densities based on the normalized soil water retention curves (SWRCs) method. After the normalization, the normalized main drying and wetting SWRCs are independent of the void ratio or bulk density. The hysteresis behavior between the normalized main drying and wetting SWRCs can be described by referring to the existing void ratio independent hysteresis model. Additionally, a simple estimation method to simulate the effects of the void ratio or bulk density on the relative permeability coefficient of unsaturated soils is proposed. The approach proposed here requires no additional parameters. The results show that the proposed hysteresis model can be used to describe the arbitrary main drying, wetting, and scanning curves at arbitrary void ratios over a wide suction range, and the predictions for the relative permeability coefficient with different void ratios by the proposed permeability model can match the experimental data well.

Laboratory Evaluation of a Vertical Vibration Testing Method for an SMA-13 Mixture

In order to simulate the on-site compaction conditions of a Stone Matrix Asphalt (SMA) mixture, The Vertical Vibration Testing Method (VVTM), Superpave Gyratory Compactor (SGC), and Marshall method are used to test the SMA-13 mixture, and the physical and mechanical properties of the asphalt mixture designed by these three methods are tested. Subsequently, the influences of the molding method on the mechanical properties are compared. The influence of vibration compaction time on the volume parameters of the SMA mixture is studied. Following the heavy traffic compaction standards, the vibration compaction time of the SMA mixture is determined. The results show that the densities of the heavy Marshall specimen, VVTM specimen, and SGC specimen are 1.018 times, 1.019 times, and 1.015 times greater than that of the standard Marshall specimen, respectively. The passing rate of the 4.75 mm aggregate of the standard Marshall specimen is 29.9%, and that of the VVTM specimen and SGC specimen is 31.1% and 30.5%, respectively, while that of the heavy Marshall specimen is 34.5%. The mechanical strength of the specimen can be greatly improved as the density increases. On the other hand, by the same compaction work, the mechanical strength of the VVTM specimens can be increased by at least 7% compared with the heavy Marshall specimen. The mechanical strength of the VVTM specimen is increased by at least 22% compared with the standard Marshall specimen. The results also show that under the optimal asphalt-aggregate ratio and the same compaction work, the compressive strength and shear strength of the VVTM specimens are increased by at least 6% and 9%, respectively, compared with the Marshall specimens. In summary, the performance of the asphalt mixture designed by the VVTM is superior, providing a wider choice for future asphalt mixture design.

A framework for modelling soil structure dynamics induced by biological activity.

Soil degradation is a worsening global phenomenon driven by socio‐economic pressures, poor land management practices and climate change. A deterioration of soil structure at timescales ranging from seconds to centuries is implicated in most forms of soil degradation including the depletion of nutrients and organic matter, erosion and compaction. New soil–crop models that could account for soil structure dynamics at decadal to centennial timescales would provide insights into the relative importance of the various underlying physical (e.g. tillage, traffic compaction, swell/shrink and freeze/thaw) and biological (e.g. plant root growth, soil microbial and faunal activity) mechanisms, their impacts on soil hydrological processes and plant growth, as well as the relevant timescales of soil degradation and recovery. However, the development of such a model remains a challenge due to the enormous complexity of the interactions in the soil–plant system. In this paper, we focus on the impacts of biological processes on soil structure dynamics, especially the growth of plant roots and the activity of soil fauna and microorganisms. We first define what we mean by soil structure and then review current understanding of how these biological agents impact soil structure. We then develop a new framework for modelling soil structure dynamics, which is designed to be compatible with soil–crop models that operate at the soil profile scale and for long temporal scales (i.e. decades, centuries). We illustrate the modelling concept with a case study on the role of root growth and earthworm bioturbation in restoring the structure of a severely compacted soil.

Copper impact on enzymatic cascade and extracellular sequestration via distinctive pathways of nitrogen removal in green sorption media at varying stormwater field conditions.

Nutrient removal efficiency in green sorption media such as biosorption activated media (BAM) for treating stormwater runoff can be heavily influenced either on a short- or long-term basis by varying field conditions of linear ditches due to the presence of copper in stormwater runoff. It is also noticeable that the linear ditch undergoes physical or mechanical impacts from the traffic compaction, chemical impact of carbon sources from the nearby farmland, and biological impact from potential animal activities (such as gopher tortoises, moles, and ants). In the nitrogen cycle, two denitrification pathways, the dissimilatory nitrate reduction to ammonia and common denitrification, are deemed critical for such assessment. A fixed-bed column study was set up to mimic different linear ditch field conditions for BAM applications and measure the effect of short-and long-term copper addition on microbial dynamics given the varying decomposition of dissolved organic nitrogen (DON). The findings confirm that, as the denitrifiers (in the second pathway) were the dominant species, their population continued to grow and maintain small-sized cells for extracellular sequestration under long-term copper impact. Furthermore, the study indicated that the ammonia oxidizer comammox was found in higher quantities than ammonia oxidizing bacteria or archaea. An enormous amount of DON was released during this process to bind the copper ion and reduce its toxicity as the enzymatic cascade effect appeared. In addition, the long-term copper exposure posed salient inhibitory effects on the microbial community regardless of varying field conditions in BAM. Short-term copper toxicity exerted an important but varying role in the enzymatic cascade effect over different linear ditch field conditions in BAM.

Fate and transport processes of nitrogen in biosorption activated media for stormwater treatment at varying field conditions of a roadside linear ditch

Roadside drainage networks can result in changes to watershed hydrology and water quality. By acting as hydrological links between urban development, agricultural fields, and natural streams, roadside ditches may be modified by filling in some green sorption media to control nitrogen pollution. Biosorption activated media (BAM), one of the green sorption media, are composed of sand, tire crumb, and clay, which can remove nitrogen from stormwater and groundwater through integrated hydrological, chemophysical, and microbial processes. The fate and transport processes of interest are complicated by internal microbial processes including ammonification, nitrification, denitrification, and dissimilatory nitrate reduction to ammonium (DNRA), each of which is controlled by different microbial species in addition to some varying field conditions. In this study, BAM was tested in a suite of columns to address site-specific physical, chemical and biological concerns driven by in situ traffic compaction, carbon availability, and animal impact (such as gopher turtles, moles, and ants) all of which impose different impacts on nitrogen fate and transport processes that may be signified by changing dissolved organic nitrogen species (DONs). The traffic compaction condition resulted in the most suitable hydraulic retention time in the hydrological process, which is beneficial for the assimilation of DONs in a long-term carbon rich environment due to biofilm expansion. Denitrifiers were the most predominant microbial population and the microbial species of DNRA were the second most predominant one in all three field conditions. However, the relationship of denitrifiers and DNRA in BAM can be shifted from commensalism to competition or even inhibition after carbon addition in microbial ecology.

Effect Forward Speed of Tractor-Implement, Its Number of Traffic and Soil Compaction Depth in Some Soil Physical Properties

Effect Forward Speed of Tractor-Implement, Its Number of Traffic and Soil Compaction Depth in Some Soil Physical Properties

Wide span – re-mechanising vegetable production

Vegetable production is characterised by intensive traffic, particularly during harvest. While tillage is used to remediate harvest-induced soil compaction and prepare seedbeds, both traffic and tillage require significant energy input and negatively impact soil physical and biological properties. Traffic compaction can be permanently eliminated from the crop growth zone by controlling traffic. This requires all implements to have a particular span, or multiple of it, and all wheel tracks to be confined to specific traffic lanes. The production, environmental and economic benefits of Controlled Traffic Farming (CTF) have been demonstrated commercially in the Australian grain and sugar industries. CTF adoption in the vegetable industry is challenged by the difficulty of achieving compatible track gauge and working width across a diverse range of equipment. Wide-span (gantry) tractors (WS) offer a new mechanization pathway for the industry. A WS tractor, spanning 6-12 m, allows multiple conventional implements of different widths to be mounted within the confinement of the span. A prototype Danish WS tractor equipped with an onion harvester shows that mounting harvest equipment on a WS platform is likely to be no more complex than modifying conventional tractor driven or self-propelled harvest machines to allow CTF. Wide, non-trafficked crop beds could provide yield increases of up to 20% in some crops, purely by growing more plants per ha of land, as less area is required for wheel tracks. Improvements in soil structure through the use of CTF can lead to further yield improvements, reduce energy use, and improve water use efficiency, infiltration and drainage. Using a mixed vegetable crop rotation as a modeling case study, it is estimated that CTF based on WS tractors could substantially improve the productivity and environmental sustainability of vegetable production.

Potential To Increase Productivity And Sustainability In Argentinean Agriculture With Controlled Traffic Farming: A Short Discussion

Abstract Drivers for and potential barriers against adoption of controlled traffic farming (CTF) systems in Argentina are reviewed. Traffic compaction is one of the main factors affecting crop productivity within Argentinean agriculture, and has significant although less quantified impacts on the whole-of-farm system. This suggests that the benefits of no-tillage (NT), which represents the dominant form of cropping in Argentina, are not fully realised. Conservative estimates indicate that crop yields could be improved by at least 15% if NT is used in conjunction with CTF. Cost-benefit analyses of available options for compaction management are required. Despite this, and based on reported evidence internationally, a shift toward increased uptake of CTF within Argentinean agriculture is likely to: (1) improve productivity and farm profitability, (2) enhance environmental performance, and (3) maintain competitiveness of the agricultural sector. Appropriate technical advice and support is a key requirement to drive adoption of CTF. Therefore, the adoption process will benefit from collaboration developed with well-established research and extension organisations in Australia and the United Kingdom, and active engagement of machinery manufacturers.

Atributos físicos de Cambissolo Háplico em vinhedos submetidos a intensidades de tráfego

Em vinhedos, o tráfego de máquinas agrícolas causa compactação do solo que pode ser mais acentuada nas entrelinhas pela maior intensidade de tráfego. Este trabalho objetivou avaliar a variabilidade dos atributos físicos do solo em razão da posição de amostragem em relação à linha de plantio, em vinhedos comerciais da variedade Bordô em pé franco, submetidos a diferentes manejos da cultura. Em fevereiro de 2012, três vinhedos foram selecionados no município de Major Gercino (SC), sendo um manejado sem a utilização de máquinas agrícolas (vinhedo 1: com seis anos de implantação) e dois que utilizam máquinas nas entrelinhas (vinhedos 2 e 3: com oito e 17 anos, respectivamente). Na linha de plantio (Lp), na linha do rodado (Lr) e entre a linha de plantio e a linha do rodado (El), foram coletadas amostras indeformadas de solo nas camadas de 0,00-0,05, 0,05-0,10, 0,10-0,15 e 0,15-0,20 m de profundidade. Avaliaram-se a densidade do solo (Ds), a resistência à penetração (Rp), as classes de poros (macroporos - MaP, mesoporos - MeP, microporos - MiP e porosidade total - PT), os índices de agregação e de estabilidade de agregados (Diâmetro médio geométrico dos agregados secos ao ar e estáveis em água - DMGsa e DMGea, índice de estabilidade de agregados - IEA), a umidade gravimétrica (Ug), a densidade das partículas e a granulometria do solo. O estado de compactação aumentou no sentido da Lp para a Lr. A ocorrência de tráfego, em geral, influenciou negativamente os atributos avaliados. Entre as posições de amostragem, os maiores valores de Ds e Rp ocorreram na Lr, em que a Rp atingiu valores críticos ao desenvolvimento de raízes; nos vinhedos mecanizados, foram encontrados elevados valores de Rp e baixos de MaP nas camadas de 0,00-0,05 e 0,05-0,10 m. Observaram-se agregados com maior diâmetro e menores IEA, o que indica deterioração da qualidade física do solo. No vinhedo 1, houve menor variabilidade dos atributos físicos, enquanto no vinhedo 2 verificou-se influência negativa do tráfego de máquinas, principalmente para os atributos relacionados à agregação e elevada MiP. No vinhedo 3, observaram-se os maiores índices de Rp e de Ds, bem como o menor valor de MaP. Portanto, em relação aos vinhedos estudados, verificou-se aumento da degradação física do solo proporcionado pelo tráfego de máquinas (vinhedos 2 e 3). Dentre as posições de coletas e os vinhedos, evidenciou-se, por meio da análise de componentes principais, a separação da posição Lr do vinhedo 3, em razão dos atributos Ds e Rp, permitindo inferir que o manejo adotado na posição Lr está ocasionando maior degradação da qualidade física do solo.

Controlled traffic for vegetable production: Part 2. Layout considerations in a complex topography

Controlled traffic farming (CTF) maintains the same machinery wheel tracks in cropping fields year after year, thereby isolating the impacts of traffic compaction from the soil used for crop growth. The benefits of CTF include reduced energy use, improved soil health and crop yield, better timeliness of field operations and improved economics.

Controlled traffic for vegetable production: Part 1. Machinery challenges and options in a diversified vegetable industry

Controlled traffic farming (CTF) maintains the same machinery wheel tracks in cropping fields year after year, thereby isolating the impacts of traffic compaction from the soil used for crop growth. Benefits of CTF include improved energy efficiency, soil health, crop yield, timeliness and economics. The successful adoption of CTF in the Australian grain and cane industries has been largely based on a limited equipment suite and flat to mildly sloping topography. The Tasmanian vegetable industry faces a very different scenario, with a wide diversity of machinery, and topography ranging from gently to steeply undulating. Two key technical challenges to the adoption of CTF in vegetable and mixed cropping were investigated – 1) working and track width compatibility of current equipment, and 2) farm layouts suited to steeply undulating topography. Almost no machines are currently compatible with a common track or working width, although some are suitable for modification to enable CTF operation. Some harvest machinery (e.g. single row potato harvesters) provides few options for change. Seasonal CTF represents a possible starting place for adoption until more compatible machinery is available. Findings in relation to farm layouts are reported in a companion paper ( McPhee, Neale, & Aird, 2013 ). • Mixed vegetable farming requires a diverse range of equipment. • Machinery incompatibility needs to be resolved to enable use of CTF in vegetables. • Seasonal CTF is an achievable start point for adoption of full CTF in vegetables. • Mixed track gauges can be accommodated with careful selection of track gauge and working width combinations.

Evaluation of Functional Properties of Porous Asphalt Pavements Subjected to Clogging and Densification of Air Voids

This study was motivated by concerns that porous asphalt concrete (PAC) might not perform well under severe environmental and traffic conditions. It was feared that the drainability, friction, and noise benefits of PACs would be rapidly lost. PAC sections were constructed with three types of asphalt: nonmodified bitumen (NMB), polymer-modified bitumen (PMB), and highly modified bitumen (HMB). These sections were completed in 2008 and evaluated twice a year for their functionality. Clogging and densification were shown to be the main reason for the reduction in PAC air voids. For the NMB and PMB sections, more than 70% of the reduction in air voids resulted from traffic compaction; this reduction was less than 30% for the HMB section. The decrease in drainability corresponded well with the decrease in air voids. Cleaning of PAC mixtures did not appear to be effective for the NMB and PMB sections because most of the reduction in air voids resulted from traffic compaction. Because of the significant amount of macrotexture produced within PAC pavement surfaces, PAC layers maintained adequate frictional characteristics even after becoming clogged and condensed. The noise characteristics of PACs depended on the air void content. No rutting, raveling, cracking, or other failures have been observed to any significant extent on the three monitored sections since they opened to traffic in 2008; these results suggest that PACs may be a viable type of pavement surface for use on highways to provide good performance, including good friction, reduced splash and spray, and reduced tire–pavement noise.

Soil Carbon Dioxide Flux in Response to Wheel Traffic in a No-Till System

Measurements of soil CO2 flux in the absence of living plants can be used to evaluate the effectiveness of soil management practices for C sequestration, but field CO2 flux is spatially variable and may be affected by soil compaction and the percentage of total pore space filled with water (%WFPS). The objectives of our study were: (i) to evaluate the effect of wheel traffic compaction on CO2 flux at two landscape positions with differing soil properties; and (ii) to examine the relationship of CO2 flux and %WFPS under field conditions and a wide range of soil porosities. Carbon dioxide flux was measured near Ames, IA, in a no-till system without living plants using the closed chamber method on nine cylinders inserted into the soil at each measurement site and evenly spaced across three rows, an untracked interrow, and a tracked interrow. Flux, volumetric water contents, and soil temperature were measured on 12 or 13 d between day of the year (DOY) 164 and 284 in 2001, 2004, and 2005. Bulk density, soil organic C concentration, and soil texture were determined after DOY 284. On most days, CO2 flux was less in the tracked interrow than in the row or untracked interrow positions. In all 3 yr, the cumulative flux of the tracked position was significantly less than one or both of the other positions. Landscape position did not affect the response of CO2 flux to traffic. Percentage water-filled pore space was not a good predictor of surface CO2 flux in the field. The effect of wheel traffic compaction on CO2 flux should be considered when soil CO2 flux is used to compare management practices.

Root growth and yield of maize as affected by soil compaction and cover crops

The yield of rainfed crops is commonly limited by the availability of soil water during the summer growing season. Channels produced by cover crop roots in fall/winter when soils are relatively moist may facilitate the penetration of compacted soils by subsequent crop roots in summer when soils are relatively dry and hard. Our objective was to determine the effects of fall cover crops on maize (Z ea mays) growth and soil water status under three levels (high, medium, and no) of imposed traffic compaction. The study was conducted on coastal plain soils (fine-loamy Typic/Aquic hapludults and siliceous, Psammentic hapludults) in the mid-Atlantic region of the United States from 2006 to 2008. Cover crop treatments were FR (forage radish: Raphanus sativus var. longipinnatus, cv. ‘Daikon’), rapeseed ( Brassica napus, cv. ‘Essex’), rye (cereal rye: Secale cereale L., cv. ‘Wheeler’) and NCC (no cover crop). Maize under high compaction achieved more deep-roots following FR and rapeseed than following rye or NCC. However, maize had greater yield following all cover crops than NCC control regardless of compaction levels and soil texture. Compaction reduced maize yield only under the high compaction in the lightly textured soils. During 24 June–24 July 2008, soils at 15 and 50 cm depths were drier under no compaction than high compaction and drier following FR than other cover crop treatments. Our results suggest that FR benefited maize root penetration in compacted soils while rye provided the best availability of surface soil water; rapeseed tended to provide both benefits. However, as rapeseed is relatively difficult to kill in spring, a mixture of FR and rye cover crops might be most practical and beneficial for rainfed summer crops under no-till systems in regions with cool to temperate, humid climates.