The soil quality concept as a tool for exposing values in science and promoting sustainability considerations

The term soil quality has mainly been used as a technical concept for grading soils. It is important that the values and goals in soil use planning and soil management are explicitly stated and related to the soil quality indicators. Such a cognitive soil quality concept may facilitate the urgent need of soil scientists to interact with stakeholders in the society. Useful approaches for such exercises have been proposed in the literature. A shift in research paradigm away from the classical, positivistic, ‘value-neutral’ approach is, however, a prerequisite for a fruitful outcome of this endeavour. The reflexive objectivity is a valuable tool in differentiating the basic scientific observations from societal priorities and personal values of the scientist. Other suggestions of associating ‘post-positivistic-science’ societal priorities to observations and experiments (e.g., ‘precautionary’ science) are strongly dissuaded. The suggested increase in focus on sustainability-based decisions on soil management induces a recommended search for ‘management thresholds’ rather than the more descriptive ‘soil quality indicator benchmarks/thresholds’. I strongly recommend the ESSC to increase its activities on prescriptive and management-oriented research and in this endeavour make use of the proposals given above

Soil Infrastructure, Interfaces & Translocation Processes in Inner Space (“Soil-it-is”): Towards a Road Map for the Constraints and Crossroads of Soil Architecture and Biophysical Processes

Soil functions and their impact on health, economy, and the environment are evident at the macro scale but determined at the micro scale, based on interactions between soil micro-architecture and the transport and transformation processes occurring in the soil infrastructure comprising pore and particle networks and at their interfaces. Soil structure formation and its resilience to disturbance are highly dynamic features affected by management (energy input), moisture (matric potential), and solids composition and complexation (organic matter and clay interactions). In this paper we review and put into perspective preliminary results of the newly started research program “Soil-it-is” on functional soil architecture. To identify and quantify biophysical constraints on soil structure changes and resilience, we claim that new approaches are needed to better interpret processes and parameters measured at the bulk soil scale and their links to the seemingly chaotic soil inner space behavior at the micro scale. As a first step, we revisit the soil matrix (solids phase) and pore system (water and air phases), constituting the complementary and interactive networks of soil infrastructure. For a field-pair with contrasting soil management, we suggest new ways of data analysis on measured soil-gas transport parameters at different moisture conditions to evaluate controls of soil matrix and pore network formation. Results imply that some soils form sponge-like pore networks (mostly healthy soils in terms of agricultural and environmental functions), while other soils form pipe-like structures (agriculturally poorly functioning soils), with the difference related to both complexation of organic matter and degradation of soil structure. The recently presented Dexter et al. (2008) threshold (ratio of clay to organic carbon of 10 kg kg-1) is found to be a promising constraint for a soil’s ability to maintain or regenerate functional structure. Next, we show the Dexter et al. (2008) threshold may also apply to hydrological and physical-chemical interface phenomena including soil-water repellency and sorption of volatile organic vapors (gas-water-solids interfaces) as well as polycyclic aromatic hydrocarbons (water-solids interfaces). However, data for differently-managed soils imply that energy input, soil-moisture status, and vegetation (quality of eluded organic matter) may be equally important constraints together with the complexation and degradation of organic carbon in deciding functional soil architecture and interface processes. Finally, we envision a road map to soil inner space where we search for the main controls of particle and pore network changes and structure build-up and resilience at each crossroad of biophysical parameters, where, for example, complexation between organic matter and clay, and moisture-induced changes from hydrophilic to hydrophobic surface conditions can play a role. We hypothesize that each crossroad (e.g. between organic carbon/clay ratio and matric potential) may control how soil self-organization will manifest itself at a given time as affected by gradients in energy and moisture from soil use and climate. The road map may serve as inspiration for renewed and multi-disciplinary focus on functional soil architecture

Soil Quality Management - Concepts and Terms

The industrialization of agriculture and the concurrent increase in societal concerns on environmental protection and food quality have put focus on agricultural management and its impact on soil quality. Soil quality involves the ability of the soil to maintain an appropriate productivity, while simultaneously reducing the effect on the environment and contributing to human health. This development has changed society’s expectations to science and there is an urgent need to improve the communication among researchers from different scientific disciplines. The interaction of scientists with decision-makers is a topic of utmost relevance for future developments in agriculture. Reflexive objectivity denotes the exercise of raising one’s consciousness of the cognitive context, i.e. societal priorities and the values and goals of the researcher. The term sustainability comprehends the priorities in the cognitive context and thus constitutes a valuable tool for expressing the basis of scientific work. Soil quality evaluations should include awareness of the stability of any given quality attribute to disturbance and stress. This implies addressing resistance and resilience of the soil functions and/or the physical form in question. Most existing literature on soil quality focuses on assessment of soil quality rather than the management tools available to influence soil quality. Identification of management thresholds rather than soil quality indicator thresholds is suggested as an important means of implementing the soil quality concept. The major challenges facing modern agriculture include proper nutrient cycling, maintained functions and diversity of soil, protection of an appropriate physical form, and avoidance of chemical contamination. It is suggested that these challenges and problems as related to the soil quality concept are discussed in the framework expounded above

Jordkvalitet, jordbrug og EU-planlægning af jordbeskyttelse – et eksempel på en proces med dansk indflydelse

• Jordkvalitet har to aspekter: 1) graduering god/dårlig og 2) behov og ønsker. Den amerikanske tilgang fokuserer næsten udelukkende på det første aspekt, hvorfor værdier og prioriteringer ikke er eksplicitte. Det giver kommunikationsproblemer og uklare løsninger • Den af DJF gennemførte udredning om effekter af jordbrugs-metoder på jordkvalitet påviste behovet for eksplicit håndtering af værdier og prioriteringer i forsknings- og planlægningsarbejde • Samme arbejde påpegede problemer med ikke-universalitet af indikatorer og – ikke mindst – indekser for jordkvalitet. I stedet peges på management-fokuseret problemløsning i tværfaglige projektgrupper • Den foreliggende EU tematiske strategi for jordbeskyttelse har gennem anvendelse af DPSIR-konceptet givet mulighed for den vigtige, eksplicitte håndtering af behov og ønsker (prioriteringer

Threats to soil quality in Denmark - A review of existing knowledge in the context of the EU Soil Thematic Strategy

The EU Commission is preparing a proposal for a Soil Framework Directive with the purpose of protecting the soil resources in Europe. The proposal identifies six major threats to the sustained quality of soils in Europe. This report addresses the threats that are considered most important under the prevailing soil and climatic conditions in Denmark: compaction, soil organic matter decline, and erosion by water and tillage. For each of these threats, the relevance and damage to soil functions as well as the geographic distribution in Denmark are outlined. We suggest a procedure for identifying areas at risk. This exercise involves an explicit identification of: i) the disturbing agent (climate / management) exerting the pressures on soil, and ii) the vulnerability of the soil to those stresses. Risk reduction targets, measures required to reach these targets, and the knowledge gaps and research needs to effectively cope with each threat are discussed. Our evaluation of the threats is based on soil resilience to the imposed stresses. Subsoil compaction is considered a severe threat to Danish soils due to frequent traffic with heavy machinery in modern agriculture and forestry. The soil content of organic matter is critically low for a range of Danish soils, which should be counteracted by appropriate management options. Soil erosion by tillage, and to a lesser degree by water, adversely affects soil quality on much of the farmland because degradation rates are much higher than generation of soil

Organic farming effects on clay dispersion in carbon-exhausted soils

Many Danish soils are depleted in organic matter (OM) after decades of intensive cereal cultivation (Schjønning et al., 2009). In this paper we show that clay particles (colloids) in soils that are low in OM content are easily dispersed in the soil water, which in turn has important effects on soil ecosystem functions and services. Organic farming systems generally tend to increase soil OM contents and may thus mitigate the negative effects

Searching the critical soil organic carbon threshold for satisfactory tilth conditions – test of the Dexter clay:carbon hypothesis

The concern for deteriorating soil structure at low soil organic matter (SOM) contents calls for better knowledge of SOM interaction with soil minerals as well as guidelines for soil conservation. We measured clay dispersibility in a field with a textural gradient. Our results support the concept of differentiating soil content of clay in a complexed and non-complexed part although our data did not point out an exact clay/OC ratio threshold. Our results also indicated that labile fractions of SOM may play an important role in soil physical behavior. We revisited literature data and found evidence that soil content of fines (<2 or <20 μm) is a major determinant of soil specific surface area (SA). We noted that soil SA coverage with SOM changed dramatically at a specific ratio of either clay (<2 μm) or clay+silt (<20 μm) with soil OC. This is an indirect support of the recently suggested quantification of the soil mineral ‘saturation’ hypothesis. More studies are needed on the causal relationships. We conclude that clay/OC~10 or (clay+silt20μm)/OC~20 are corresponding indices reflecting shift in soil physical behavior

Carbohydrates in hot water extracts of soil aggregates as affected by long-term management

Microbial carbohydrates are immediate by-products of microbial metabolism and play an important role in the formation and stabilization of soil structure. The effect of long-term management on soil carbohydrate content and monosaccharide composition was investigated in five. Danish sandy loams under organic and conventional management with animal manure and mineral fertilizers. Hot-water (80°C)extraction was used to measure the distribution and composition of carbohydrates in aggregate size. Carbohydrates released to hot water were determined after hydrolysis as reducing sugars equivalent to glucose. The monosaccharide composition in hot-water extracts was analyzed as the corresponding alditol acetates. Sites with a history of long-term continuos management practices were used. Three treatments from the >100 year Askov long-term field experiment were used to show results of contrasting fertilization on soil carbohydrate content. These were all grown to a four-course crop rotation. Total carbohydrate content was signifcantly infuenced by long-term management practices, with a signifcantly higher carbohydrate content in soils fertilized with either mineral fertilizers or animal manure (1200 to 800 mg C kg-1 DM aggregate)than in an unfertilized soil (600 to 500 mg C kg-1 DM aggregate). These results were as true for micro-aggregates (,0.25 mm)as for the 0.5–1. 0mmand 4.0–8.0 mm fractions. The organically managed soil (>40years) was sited at a commercial farm with forage crop rotations, organic manure and nouse of crop protection chemicals. These results showed signifcantly higher levels of carbohydrate both in micro-aggregate and macro-aggregates (1200 to 900 mg C kg-1 DM aggregate) than an adjacent conventionally managed soil with annual cash crop, mineral fertilizers and use of cropprotection chemicals (960 to 760 mg C kg-1 DM aggregate). Carbohydrate Ccontent generally increased as aggregate size decreased in both soils. Monosaccharide distribution was generally similar among three aggregate size classes studied. In all soils the content of monosaccharide was highest in micro-aggregates and lowest in macro-aggregates. Mannose and galactose were normally the most common monosaccharides in the hot-water extracts of aggregate fractions, indicating a predominantly microbial origin

Er der krummer i din jord – eller er det bare knolde

Jordens krummer er vigtige for vækst. Både vækst af afgrøden og de svampe og bakterier, der laver bindemidler til nye krummer. Vi har undersøgt, hvordan praktisk økologisk og konventionel drift påvirker dette samspil. Et varieret sædskifte med meget græs og husdyrgødning gav gode stabile krummer med højt indhold af biologiske bindemidler. Et ensidigt kornsædskifte med kunstgødning gav i stedet stabile knolde, hvor bindemidlet var ler. Sådan nogle knolde kan give et dårligt såbed, fordi våd jord bliver blød som mudder og tør jord hård som beton

Soil aggregation – a matter of proper management

Soil crumbs are important to soil functions. These include plant growth, and the growth of fungi and bacteria forming agents for binding and bonding of new crumbs. We have studied how commercial organic and conventional farming affect this interaction. A diverse crop rotation, including grass, and animal manure resulted in stable crumbs with a high content of biological binding and bonding agents. A cash crop rotation with the addition of only synthetic fertilizers resulted in small, stable aggregates – more like clods - with clay as binding agent. Such a soil will provide poor conditions for preparing seedbeds, because prolonged rain makes it soft and muddy while drought makes it hard as brick