Macro- and microscale gaseous diffusion in a Stagnic Luvisol as affected by compaction and reduced tillage

Intensification of mechanical agriculture has increased the risk for soil compaction and deformation. Simultaneously, reduced tillage practices have become popular due to energy saving and environmental concerns, as they may strengthen and improve the functioning of structured soil pore system. Soil aeration is affected by both compaction and reduced tillage through changes in soil structure and in the distribution of easily decomposable organic matter. We investigated whether a single wheeling by a 35 000 kg sugar-beet harvester in a Stagnic Luvisol derived from loess near Göttingen, Germany, influenced the gas transport properties (air permeability, gaseous macro- and microdiffusivities, oxygen diffusion rate) in the topsoil and subsoil samples, and whether the effects were different between long-term reduced tillage and mouldboard ploughing. Poor structure in the topsoil resulted in slow macro- and microscale gas transport at moisture contents near field capacity. The macrodiffusivities in the topsoil under conventional tillage were slower compared with those under conservation treatment, and soil compaction reduced the diffusivities by about half at the soil depths studied. This shows that even one pass with heavy machinery near field capacity impairs soil structure deep into the profile, and supports the view that reduced tillage improves soil structure and aeration compared with ploughing, especially in the topsoil

The Belgian Contribution to Global 1968

The calendar year of 1968 is almost universally associated with student unrest. Belgium fits into this picture rather well, with major student mobilisations in Leuven and Brussels occurring in the first half of that notoriously restless calendar year.1 Yet all-inclusive assessments of the social movements and political reconfigurations happening that year, not only in Belgium but elsewhere in Europe and North America as well, must go beyond the relatively narrow confines of university student milieus. For the purposes of this essay, I propose also to address fresh developments occurring within the worlds of labor and cultural productions. In terms of political developments, particular attention will be placed on discussions affecting the forces composing the traditional Old Left, i.e. social democracy and communism, with special emphasis given to the rise of a New and – eventually – a Far Left. Mention will likewise be made of important reverberations of such trends in the lifeworld of Catholicism. Leaving aside certain national peculiarities, all aforementioned categories of analysis are crucial for an understanding of 1968 around the world (...)

Modifications of soil physical properties of forest floor horizons at previously fly ash affected forest sites in the region Upper Lusatia

In dieser Studie wird der Einfluss überwiegend historischer atmosphärischer Flugaschedepositionen auf physikalische Eigenschaften von Waldböden und insbesondere deren Humusauflagen untersucht. Es werden sechs Leitprofile der Region Oberlausitz mit und ohne Flugascheanreicherungen vorgestellt. Die flugascheangereicherten Standorte sind geprägt durch 1,0 bis 1,5 dm mächtige Durchmischungshorizonte (Humusauflage mit Flugasche), die extrem stark durchwurzelt sind. Die reinen Humusauflagen sind geringmächtiger (< 0,6 dm) und auch weniger stark durchwurzelt. Im Vergleich mit reinen Humusauflagen zeigen die flugascheangereicherten zum Teil signifikant höhere Luftkapazitäten, gesättigte Wasserleitfähigkeiten und Festsubstanzdichten, wohingegen emittentennah die nutzbaren Feldkapazitäten geringer sind. Für die flugascheangereicherten Standorte wurden mineralische Flugascheanreicherungen von 150 bis 280 t/ha berechnet, wobei emittentennähere Standorte höhere Werte aufweisen. Zeitweise Vernässung und anstehendes Ausgangsgestein schränken die Durchwurzelbarkeit stark ein. Die nutzbare Feldkapazität des effektiven Wurzelraums nFKWe ist daher deutlich von den Eigenschaften der Auflagen und des Oberbodens geprägt. Die flugascheangereicherten Humusauflagen stellen 20 bis 42% der nFKWe, die reinen Humusauflagen nur 8 bis 16%.This study describes the influence of predominantly historical atmospheric depositions of lignite fly ashes upon physical properties of forest soils and especially of forest floor horizons. We compared 6 soil profiles with and without fly ash enrichment in the region Upper Lusatia, Eastern Germany. Fly ash enriched sites have a 1.0 to 1.5 dm thick and densely rooted top horizon consisting of a mixture of humus and fly ash. Uncontaminated forest floor horizons are less thick (<0,6 dm) and less rooted. Fly ash enriched forest floor horizons show higher air capacities, saturated conductivities and particle densities, whereas plant available water is reduced emission source close. Deposition rates were estimated at 150 to 280 t/ha, whereby at sites located close to the emission source the highest values were calculated. The vertical root development of the trees is constrained at locations characterized by temporary water logging and shallow soils with surface-near bedrock. Hence, properties of forest floor horizons and the mineral top soil condition plant available water in the effective root zone. Fly ash enriched forest floor horizons amount to 20 to 42% of plant available water in the effective root zone, whereas uncontaminated forest floor horizons only amount to 8 to 16%

Impact of Small-Scaled Differences in Micro-Aggregation on Physico-Chemical Parameters of Macroscopic Biopore Walls

Macroscopic biopores, like earthworm burrows or channels which remain after a root decayed, act as preferential flow paths for water, gas, and heat transport processes, and viewing at agricultural production, as preferential elongation paths for plant roots. These processes result in intense alterations of the soil volume and its composition that surrounds the pores. The effects of these processes were analyzed at small-scale and physico-chemical soil parameters, i.e., relative oxygen diffusion coefficient (Ds/DO), oxygen partial pressure pO2, Eh and pH of biopore walls, were measured. The analyses were carried out on undisturbed soil samples with different colonization history, excavated from a haplic Luvisol derived from loess. Soil resistance to penetration was determined simultaneously with Ds/DO and pO2 using a coupled, self-developed approach, and four matric potentials (namely, Ψm = −1 kPa; −3 kPa; −6 kPa or −30 kPa) were considered. We hypothesized that physico-chemical soil parameters in biopore walls were altered due to differing influences on the soil aggregation. Aggregation was visualized with scanning electron microscopy, classified and used to explain differences in–soil properties. Plant roots and earthworms altered aggregation next to biopore surfaces in a contrasted way, either by enhancing aggregates diversity or homogenizing it. Roots led to the formation of subpolyeders while earthworms formed subplates. Pore functions of microaggregates were comparable to those of larger scale, and subpolyeders showed much more favorable soil properties in terms of soil aeration (Ds/Do, pO2). Replicates of all parameters scattered intensely and showed deviations up to several orders of magnitude in case of Ds/DO underlining the large variability of soil properties in biopore walls

Approaches to investigate the crack formation of mineral landfill liner systems

The municipal landfill in Rastorf (Schleswig-Holstein) is covered with a temporary till based capping system. Investigations of structural changes (water conductivity, pore function, shrinkage behaviour) were carried out with undisturbed soil cores and two- and three-dimensional measurement techniques. The usage of different techniques to evaluate the soil volume changes resulted in variations of the available water capacity (ver>ver+hor>3D) and the unsaturated hydraulic conductivity. In summary, a critical matric potential between -500 and -1000 hPa in conjunction with a low shrinkage tendency (Vs < 5 %) could be seen as main argument for the utilization of till as sealing substrate

Shrinkage Characteristics of Boulder Marl as Sustainable Mineral Liner Material for Landfill Capping Systems

The soil shrinkage behavior of mineral substrates needs to be considered for engineering long-term durable mineral liners of landfill capping systems. For this purpose, a novel three-dimensional laser scanning device was coupled with (a) a mathematical-empirical model and (b) in-situ tensiometer measurements as a combined approach to simultaneously determine the shrinkage behavior of a boulder marl, installed as top and bottom liner material at the Rastorf landfill (Northern Germany). The shrinkage behavior, intensity, and geometry were determined during a drying experiment with undisturbed soil cores (100 cm 3 ) from two soil pits; the actual in-situ shrinkage was also determined in 0.2, 0.5, 0.8, and 1.0 m depth by pressure transducer tensiometer measurements during a four-year period. The volume shrinkage index was used to describe the pore size dependent shrinkage tendency and it was classified as low (4.9%) for the bottom liner. The in-situ matric potentials in the bottom liner ranged between −100 and −150 hPa, even during drier periods, thus, the previously highest observed drying range (pre-shrinkage stress) with values below −500 hPa and −1000 hPa was not exceeded. Therefore, the hydraulic stability of the bottom liner was given

Buffer zone water repellency: effects of the management practice

Water repellency index R was measured in a heavy clay and a sandy loam, used as arable land or buffer zone (BZ). Further, effect of management practise and ageing of BZs were studied. Water repellency was proved to be a common phenomenon on these soils. Harvesting and grazing increased water repellency as does ageing.Low water repellency is supposed to prevent preferential flows and provide evenly distributed water infiltration pattern through large soil volume, which favours nutrient retention

Influences bibliographiques sur la « génération 68 »

Remarques méthodologiques La formation culturelle et intellectuelle de la « génération 68 » est une question souvent abordée dans la littérature autobiographique ou biographique des principaux acteurs, sans jamais toutefois être étudiée en profondeur. Il y a, bien sûr, toute une gamme de raisons qui expliquent la marginalisation de cette question. Les biographies et autobiographies, malgré une floraison assez récente, sont encore rares et cette production demeure très inégale en ce qui concer..