Soil Fragmentation and Friability. Effects of Soil Water and Soil Management

Soil fragmentation is a primary aim in most tillage operations in order to create a soil environment favourable for crop establishment and growth. Soils vary around the world from those exhibiting a self-mulching nature to those of a hardsetting nature. These extremes have been reported for Australian and other tropical and subtropical soils. In humid temperate climates, soil tillage is generally needed in order to produce a favourable environment for crop establishment and growth. The ease of preparing a favourable arable layer depends on complex interactions between climate, soil and the tillage implement. Especially soil water affects soil strength and fragmentation properties and thereby the ease of preparing a suitable arable layer. Soil management affects soil fragmentation and friability indirectly through effects on soil structure formation and stabilization and directly through the influence of soil tillage and traffic. The overall purpose of this thesis is to contribute to the understanding of soil fragmentation and friability as affected by soil management and soil water regime. The reaction of the soil upon tillage was evaluated within the concept of soil tilth as defined by Soil Science Society of America (SSSA) "the physical condition of soil as related to its ease of tillage, fitness as a seedbed, and its impedance to seedling emergence and root penetration". The study involved soils from two case studies, the Askov long-term experiment on animal manure and mineral fertilizers, a field experiment with non-inversion tillage and a field experiment on compaction and intensive tillage. All the soils included in the study were humid sandy loams predominantly developed on Weichselian glacial moraine deposits. The soils were classified as Oxy aquic Agriudolls/Glossic Phaeozems according to Soil Taxonomy/WRB except for the Askov soil that was classified as Ultic Hapludalfs/Dystric Luvisols according to Soil Taxonomy/WRB. For all soils the clay content ranged from about 12 to 21 g per 100g-1 and soil organic matter ranged from 1.8 to 3.9 g 100g-1. The case studies included two long-term forage cropping system soils with a grass ley in the crop rotation (DFG(1) and DFG(2)), which were compared with a neighbouring counterpart. DFG(1) was compared with a forage cropping system soil without grass ley in the crop rotation (i.e., only annual crops), labelled DFA, whereas DFG(2) was compared with a continuously cash cropped soil with very low input of organic matter (no animal manure and straw removed), labelled CCC. An unfertilized (UNF), animal manured (AM) and a mineral fertilized (NPK) soil was included from the Askov long-term experiment on animal manure and mineral fertilizers established in 1894. The tillage experiment included a non-inversion tilled soil, labelled NINV, (non-inversion subsoil loosening to 35 cm depth and seedbed preparation with rotovator) and a conventionally tilled soil, labelled CONV, (mouldboard ploughing to 22 cm and secondary tine cultivation). The experiment on soil compaction and intensive tillage involved two "extreme" tillage and traffic treatments and a reference treatment (REF). The extreme treatments were soil compaction (PAC) and intensive tillage (INT) that were performed on wet soil just after spring ploughing and prior to seedbed preparation. The field experiments on non-inversion tillage, and soil compaction and intensive tillage were both conducted at the organically managed Rugballegård Research Station. Ease of tillage is commonly extrapolated from measurement of tensile strength in a compression test using air-dry or oven-dry aggregates. This procedure may lead to erroneous conclusion on soil behaviour of moist soil in the field. Therefore a multi-level analytical strategy was followed, i.e., soil fragmentation and friability were characterized using qualitative and quantitative in situ, on-field and laboratory methods. Soil fragmentation and friability were assessed in the field qualitatively by visual examination and quantitatively by employing a simple drop-shatter fragmentation test, denoted soil drop test. The energy input in the soil drop test was low in comparison with the energy input in typical seedbed cultivation. However, the soil drop test was sensitive enough to display significant differences between treatments in most cases. In the laboratory soil fragmentation and friability were evaluated by measuring tensile strength and specific rupture energy on field-sampled aggregates. In general, tensile strength was determined on air-dry aggregates and in some cases on aggregates adjusted to pressure potentials in the range -100 hPa to -166 MPa (air-dry). In addition, a direct tension test was developed to measure tensile strength of moist soil without making assumptions on the mode of failure. Undisturbed field-sampled soil cores were used in the test. The method was applicable at high matric potentials (-50 and -100 hPa) but not at -300 hPa. The direct tension test results corresponded well with the predicted values determined from the indirect measurements of aggregate tensile strength. In general, a fairly good agreement was found between the different methods in the hierarchy of methods applied. This indicates that sophisticated laboratory methods for assessing soil strength and fragmentation characteristics may well be used for evaluating soil behaviour under conditions prevailing in the field at the time of tillage. Nevertheless, it is recommended that laboratory methods are evaluated by using simple field methods at times and soil conditions appropriate for tillage. The friability index showed in general a low sensitivity to long- and short-term differences in soil management. However, a clear effect of soil water was found, i.e. maximum friability index values at -300 to -1000 hPa pressure potential. The effect of soil water on tensile strength and specific rupture energy of aggregates and on estimation of friability was investigated. As expected the study revealed the paramount influence of soil water. Interactions between soil water regime and treatment were found for cropping system soils (DFG(2) vs. CCC) and the fertilization treatments (UNF, NPK and AM) but not for the compaction treatments (PAC vs. REF). It was concluded that it might be hazardous to characterize soil fragmentation and friability properties of different treatments based on measurements at a single pressure potential and significant influence of pore characteristics was detected. Macroporosity was found to correlate to tensile strength and friability index. However, a clear correlation between tensile strength properties and pore geometry characteristics (e.g. tortuousity and continuity) was not shown. This may be due to large small-scale variations in these properties, i.e. the samples for tensile strength determination were taken next to the samples for pore characterization. Marked long-term effects of cropping systems and fertilization were found. For two neighbouring soils with a high input of organic matter, poorer soil mechanical characteristics were found for a soil with grass in the rotation (DFG(1)) than for a soil solely grown with annual crops (mainly cereals). This difference in strength and friability characteristics may be related to a higher amount of biological structural binding and bonding agents in the soil with grass included in the rotation. Two soils with high inputs of organic matter (DFG(2) and AM) displayed more desirable aggregate strength and soil fragmentation characteristics than their counterparts (CCC and UNF, respectively) receiving low inputs of organic matter. Evidence suggests that cementation of dispersed clay was a determining factor for the stronger increase in aggregate tensile strength with increased dryness (decreased pressure potential) found for the CCC and UNF soils receiving low inputs of organic matter compared with DFG(2) and AM. An early-stage effect of non-inversion tillage treatment (NINV) resulted in a poorer soil tilth in the topsoil layer (i.e., higher soil strength and lower ease of fragmentation and friability index) than for a conventionally mouldboard ploughed soil (CONV). Surprisingly, the effect of tillage on topsoil tilth was clearer by the end of the growing season in September than in May. This indicates that natural soil processes occurring during the growing season were not able eliminate the differences between the primary tillage treatments. Soil compaction (PAC) resulted in strongly increased aggregate tensile strength at all the investigated water regimes (i.e., pressure potentials: -100 hPa to -166 MPa) in comparison with a reference treatment (REF). Surprisingly, soil compaction did not significantly affect the specific rupture energy of the aggregates. This was related to a clear difference in the stress-strain relationship for the soils. Aggregates from the compacted soil failed at higher stress but at lower strain than aggregates from the reference soil (i.e., higher Young modulus, (Y/()). This was characteristic for all size-classes and at all pressure potentials. The results obtained in this study indicate that the prediction of soil fragmentation from tensile strength properties of soil elements may be very complex. We need more basic understanding of the fragmentation of "unconfined" soil at the different size-scales (aggregates to bulk soil) and the correlation between the different scales in order to be able to predict soil fragmentation in tillage (mainly superficial tillage) from a priori information. More specifically, the role of soil biology and soil water and pore characteristics needs to be studied in further detail. The development of new methods and the application of well-know methods to quantify soil fragmentation and friability of soil at conditions similar to soil conditions at tillage (including water content) has been a primary aim in this thesis. However, there is still a strong need to develop new methods and modify existing methods to quantify soil fragmentation and friability under controlled conditions. This study shows that soil compaction and intensive tillage significantly influence soil fragmentation and friability. Increasingly heavier machinery and - to some extent - more intensive seedbed preparation (PTO-driven implements) are being used in Danish agriculture. A thorough evaluation of this development on soil fragmentation and friability is needed. Furthermore, the accumulated knowledge of soil fragmentation and tensile failure in soil ought to be implemented in the design of new tillage implements

Danish and British Protection from Disability Discrimination at Work - Past, Present and Future.

Denmark and the United Kingdom both became members of what is now the European Union (EU) in 1973 and are thus equally matched in terms of opportunity to bring their anti-discrimination laws into line with those of the EU and other supra-national bodies such as the United Nations (UN) and the Council of Europe. Our investigation, based on existing reports, academic analysis and case law rulings involving alleged discrimination on grounds of disability, has revealed some major differences in the level of protection provided by each country’s legislature and judicature, but also by other mechanisms that extend beyond these traditional measures, such as workplace collective agreements.While the UK has a long history of supporting people with disabilities by legislating in all aspects of society, Denmark has been at the forefront with social mechanisms, but has been reluctant to ensure equality in the labour market. However, both countries have been equally unsuccessful in ensuring opportunities for disabled workers, and consideration is given here as to whether one system of dealing with this is better than another. We conclude that neither strict regulation imposed by the EU or national governments, nor the laissez-faire method of leaving the level of protection to be decided by collective agreement is entirely satisfactory. A different perspective altogether would be to adopt the substantive diversity theory which would focus on a person’s abilities and what they are able to do, and to gear society to embrace diversities, as the Danish employment agency Specialisterne has done so successfully in the case of adults with autism. Countries such as Denmark and the UK have much to learn from each other to tackle successfully this last bastion of workplace inequality

Non-inverting Tillage: Early-Stage Effects on Soil Mechanical Behaviour

Organic farmers often claim positive effects of non-inverting and reduced tillage systems. There is a need of quantifying tilth characteristics in the former plough layer of soil converted to such tillage systems. A non-inverting tillage system (NINV) was tested in a field experiment conducted on a Danish sandy loam soil. It included deep loosening and shallow intensive cultivation and was compared to a conventional ploughing-harrowing tillage system (CONV). A hierarchical analytical procedure was applied in studies of soil fragmentation and soil strength characteristics for the 7-14 cm soil layer. A visual description was carried out and ease of fragmentation was evaluated in the field using a soil drop test. Soil strength was measured in the field with a cone penetrometer and a torsional shear box method, and in the laboratory using an annulus shear strength method. Tensile strength was determined in the laboratory on field-sampled aggregates. The CONV treated soil displayed a higher ease of fragmentation in the field in May as well as in September. In general, aggregates from the NINV treated soil were stronger than aggregates from the CONV treatment. The soils had similar friability indices in May. In September, however, a higher friability index was found for the CONV treated soil (k=0.22 and 0.16, respectively for CONV and NINV). The NINV treated soil also displayed the highest soil strength. The soil tilth was evaluated to be best in the CONV treated soil. Supposed meliorating actions during the growing season did not eliminate the differences between the treatments

Biotic and abiotic binding and bonding mechanisms in soils with long-term differences in management

During the last decades Denmark has experienced a growing interest in low-input farming systems like organic farming. These systems rely on a high soil fertility to maintain nutrient availability and plant health. Soil aggregation contributes to this fertility, because it is crucial to soil porosity, aeration and infiltration of water. This paper reports a study of two pairs of differently managed, neighboring fields. The aim was to elucidate long-term effects of the different farming systems on physical and biological variables with influence on bonding and binding mechanisms of soil aggregation. Each pair consists of an organically grown dairy farm soil, based on a forage crop rotation system, including grass (Org-FCS(G)) and a conventionally managed soil. One of the conventional farms has a forage crop rotation with annual cash crops and no grass (Conv-FCS(NG)) and one has been grown continuously with small grain cereals and rape (Conv-CCS). Our results indicate that the Org-FCS(G) soils stimulate biotic soil aggregating agents as measured by extracellular polysaccharides (EPS) and hyphal length measurements, respectively. Generally, the Conv-CCS soil, which relies exclusively on synthetic fertilisers and cereal production, offered poor conditions for the biotic binding and bonding agents. Nevertheless this soil contained a large amount of stable macro-aggregates. This is explained by the physical results, which indicated that the strong macro-aggregation was due to clay dispersion and cementation processes rather than to biotic processes

Multi-level assessment of soil quality – linking reductionistic and holistic methodologies

Soil quality is often used as a qualitative, general term. However, quantification is an important feature of the scientific approach to nature. On the other hand, addressing specific soil parameters as indicators of soil quality includes a reduction of the whole soil system. Therefore, results obtained by specialized methodologies ought to be evaluated by methods integrating the soil characteristics in situ. In this presentation, results are given from an investigation of the tilth of two differently managed loamy soils. One of the soils had been managed for decades with a forage crop system (labeled FCS), which included fertilization with farmyard manure, while the other had been grown with a continuous cereal system (labeled CCS), receiving no input of organic matter. In the field, the structure of the top 30-cm soil layer was described visually (spade analysis) and by studying the fragmentation behavior (soil drop test). Further, the field measurements included determination of soil strength by a torsional shear box method. In the laboratory, shear strength was determined on bulk soil sampled in metal cylinders, and tensile strength was estimated from crushing tests of individual, differently sized aggregates. The FCS soil appeared porous, with crumbs as structural units, while the CCS soil was compact with blocks as structural units. The soil drop test yielded the highest degree of fragmentation for the FCS soil. The torsional shear box method showed the CCS soil to have the highest bulk soil strength. This was confirmed by the laboratory shear annulus method. Finally, the tensile strength measurements revealed a much higher strength of 8-16, 4-8 and 2-4 mm dry aggregates from the CCS soil as compared to the FCS soil, while 1-2 mm aggregates were strongest in the FCS soil. This indicates a higher friability for the FCS soil, which is in accordance with the soil behavior in the field tests. In conclusion, the quality of the FCS soil – as evaluated by its mechanical behavior – was found to be higher than that of the CCS soil. An important result is the good correlation between the integrating field methods and the differentiating laboratory methods. This means that the quantifying, reductionistic scientific approach is not conflicting with the ‘holistic’ descriptions in the field

A Comparison of Continuously Controlled and Controlled K-theory

We define an unreduced version of the e-controlled lower $K$-theoretic groups of Ranicki and Yamasaki, and Quinn. We show that the reduced versions of our groups coincide (in the inverse limit and its first derived, $\lim^1$) with those of Ranicki and Yamasaki. We also relate the controlled groups to the continuously controlled groups of Anderson and Munkholm, and to the Quinn homology groups of Quinn

The literary representation of reality

This article presents a reflection of the epistemological question of literary representation of reality. The epistemological status of literature is not obvious, because literature is fictional. Therefore, it is not evident in what way literature represents reality and to what degree the literary representation is true in the corresponding sense of the word. Through an exploration of Proust and his reflections on the same question in A la recherche du temp perdu, this article will analyse the representational question. This analysis will focus on a conflict between an essential understanding of truth, detached from the temporal reality, and a superficial referential realism. It will present an alternative phenomenological and semiotic realism, which connects the specific description in literature with a general conceptual level. In addition, the relationship between the perceptual and conceptual level will further be linked to cognitive semantics and Lakoff’s concept of cognitive models

Oplevelsesdesign - et metasemiotisk fænomen

 Artiklen karakteriserer det nye fænomen oplevelsesdesign som et metasemiotisk fænomen, der udgør en reaktion på det postmoderne meningstab. Oplevelsesdesign bestemmes om en redefinering af oplevelsesøkonomi, der fokuserer på, at det er design, og mere præcist den æstetiske formgivning, der skaber oplevelser. Artiklen beskriver det postmoderne meningstab med afsæt i Baudrillard og Lyotard, og undersøger oplevelsesdesign igennem en række eksempler, som udviser et særligt fokus på æstetik og refleksion som en bestræbelse på at skabe mening på en ny måde. Desuden beskrives konceptuel design som et særligt tydeligt eksempel på den metasemiotiske tendens