Soil Processes

Understanding soil systems is critical because they form the structural and nutritional foundation for plants and thus every terrestrial habitat and agricultural system. In this paper, we encourage increased use of mathematical models to drive forward understanding of interactions in soil ecological systems. We discuss several distinctive features of soil ecosystems and empirical studies of them. We explore some perceptions that

Current agriculture in Europe is predominantly reliant upon external inputs, such as fertilisers and pesticides, rather than upon soil processes, for the resources it needs for crop growth. Inputs of fertilisers have environmental disbenefi ts, some of which have been highlighted by the introduction of the Water Framework Directive. Here we review the scope to improve current production systems so as to reduce environmental impact while broadly maintaining productivity. The review focuses upon both the potential impacts of means of increasing soil nutrient supply, in the absence of fertilisers, and the potential impact on nutrient uptake of modifi cations to the functioning of the root system. Assessments of the functioning of the root system must allow for all root types and for the contribution of arbuscular mycorrhizal fungi (AMF). The development of productive systems based around soil processes will thus depend upon both better management of soil processes, especially when they relate to holding nutrients such as nitrogen within the system, and to developments in understanding roots and their associated microbes.

After several decades of unquestioned success, agriculture is now facing important global problems. Huge increases in productivity in developed countries have been accompanied by a severe depletion of "soil quality" in terms of resistance to erosion, organic contents, concentrations of heavy metals, and pesticide residues. Agricultural intensification in developing countries has been less successful because of various socioeconomic limitations. Nevertheless, traditional agricultural practices do not conserve the quality of soils; stocks of organic matter are rapidly becoming depleted, and erosion removes fine particles from the soil surface horizons. In a context of increasing human population pressures, particularly in developing countries, this degradation of soils results in many social and environmental problems (Eswaran 1994; FAO 2000). Features common to all kinds of soil degradation are a significant decrease in organic reserves, degradation of the soil structure, and severe depletion of soil invertebrate communities, especially earthworms (Decaëns et al. 1994; Lavelle et al. 1994). The contributions of earthworms to soil fertility have been described in several hundreds articles and books (Lee 1985; Edwards and Bohlen 1996; Lavelle and Spain 2001). This has led to a growing expectation from soil users for provision of methods that protect soil fertility through the enhancement of biological processes. Earthworms may be considered a biological resource for farming systems, and the management of earthworm communities provides a promising field for innovation in agricultural practices (Lavelle et al. 1999). Demand for techniques, making use of earthworms as a resource, is likely to increase, although basic research is still needed to support such developments.

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Forest thinning to protect the soil and improve hydrologic function is used to alter stand structure and increase residual tree growth. However, little is known about how surface and belowground wood decomposition (i.e., soil process changes) respond to aboveground vegetation manipulation. We determined mass loss of three species of wood stakes (loblolly pine (Pinus taeda L.), trembling aspen (Populus tremuloides Michx.), and Chinese pine (Pinus tabuliformis Carriére)) placed horizontally on the soil surface and vertically in the mineral soil after thinning a Chinese pine plantation in northern China. Restoration thinning treatments consisted of three levels of overstory removal (30%, 41% and 53% of the standing biomass) plus an unthinned control. Stakes were extracted every 12 months for 2years, and then at 6 month intervals until the end of the study (3.5 years). Surface stake mass loss was significantly greater (9.0%) in the 30% overstory removal treatment than the control, but overall mass loss at the soil surface was very low (< 10%) after 3.5 years. In the mineral soil, aspen stake mass loss was greater than either Chinese or loblolly pine stakes, which had similar mass loss. In addition, mass loss was greatest in the 41% overstory removal plots. Stakes of all species decomposed faster deeper in the mineral soil than near the soil surface, but they were not affected by changes in soil N, OM, and pH after thinning. Overall, thinning this Chinese pine stand had little impact on surface and belowground wood stake decomposition.

After several decades of unquestioned success, agriculture is now facing important global problems. Huge increases in productivity in developed countries have been accompanied by a severe depletion of "soil quality" in terms of resistance to erosion, organic contents, concentrations of heavy metals, and pesticide residues. Agricultural intensification in developing countries has been less successful because of various socioeconomic limitations. Nevertheless, traditional agricultural practices do not conserve the quality of soils; stocks of organic matter are rapidly becoming depleted, and erosion removes fine particles from the soil surface horizons. In a context of increasing human population pressures, particularly in developing countries, this degradation of soils results in many social and environmental problems (Eswaran 1994; FAO 2000). Features common to all kinds of soil degradation are a significant decrease in organic reserves, degradation of the soil structure, and severe depletion of soil invertebrate communities, especially earthworms (Decaëns et al. 1994; Lavelle et al. 1994). The contributions of earthworms to soil fertility have been described in several hundreds articles and books (Lee 1985; Edwards and Bohlen 1996; Lavelle and Spain 2001). This has led to a growing expectation from soil users for provision of methods that protect soil fertility through the enhancement of biological processes. Earthworms may be considered a biological resource for farming systems, and the management of earthworm communities provides a promising field for innovation in agricultural practices (Lavelle et al. 1999). Demand for techniques, making use of earthworms as a resource, is likely to increase, although basic research is still needed to support such developments.

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Covering extensive parts of China, karst is a critically important landscape that has experienced rapid and intensive land use change and associated ecosystem degradation within only the last 50 years. In the natural state, key ecosystem services delivered by these landscapes include regulation of the hydrological cycle, nutrient cycling and supply, carbon storage in soils and biomass, nutrient cycling, biodiversity and food production. Intensification of agriculture since the late-20 th century has led to a rapid deterioration in Critical Zone (CZ) state, evidenced by reduced crop production and rapid loss of soil. In many areas, an ecological 'tipping point' appears to have been passed as basement rock is exposed and 'rocky desertification' dominates. This paper reviews contemporary research of soil processes and ecosystems service delivery in Chinese karst ecosystems, with an emphasis on soil degradation and the potential for ecosystem recovery through sustainable management. It is clear that currently there is limited understanding of the geological, hydrological and ecological processes that control soil functions in these landscapes, which is critical for developing management strategies to optimise ecosystem service delivery. This knowledge gap presents a classic CZ scientific challenge because an integrated multidisciplinary approach is essential to quantify the responses of soils in the Chinese karst CZ to extreme anthropogenic perturbation, to develop a mechanistic understanding of their resilience to environmental stressors, and thereby to inform strategies to recover and maintain sustainable soil function.

After several decades of unquestioned success, agriculture is now facing important global problems. Huge increases in productivity in developed countries have been accompanied by a severe depletion of "soil quality" in terms of resistance to erosion, organic contents, concentrations of heavy metals, and pesticide residues. Agricultural intensification in developing countries has been less successful because of various socioeconomic limitations. Nevertheless, traditional agricultural practices do not conserve the quality of soils; stocks of organic matter are rapidly becoming depleted, and erosion removes fine particles from the soil surface horizons. In a context of increasing human population pressures, particularly in developing countries, this degradation of soils results in many social and environmental problems (Eswaran 1994; FAO 2000). Features common to all kinds of soil degradation are a significant decrease in organic reserves, degradation of the soil structure, and severe depletion of soil invertebrate communities, especially earthworms (Decaëns et al. 1994; Lavelle et al. 1994). The contributions of earthworms to soil fertility have been described in several hundreds articles and books (Lee 1985; Edwards and Bohlen 1996; Lavelle and Spain 2001). This has led to a growing expectation from soil users for provision of methods that protect soil fertility through the enhancement of biological processes. Earthworms may be considered a biological resource for farming systems, and the management of earthworm communities provides a promising field for innovation in agricultural practices (Lavelle et al. 1999). Demand for techniques, making use of earthworms as a resource, is likely to increase, although basic research is still needed to support such developments.

Understanding soil systems is critical because they form the structural and nutritional foundation for plants and thus every terrestrial habitat and agricultural system. In this paper, we encourage increased use of mathematical models to drive forward understanding of interactions in soil ecological systems. We discuss several distinctive features of soil ecosystems and empirical studies of them. We explore some perceptions that

The spatial distribution of soil constituents at the micrometer scale is of great importance to understand processes controlling the formation of micro-aggregates and the stabilization of organic carbon. Here, the spatial distribution of organic and mineral constituents in Podzol horizons is studied by concerted measurements of (i) the content of various forms of Fe, Al, Si and C determined by selective extraction in the fine earth fraction of soil (f < 2 mm); (ii) the elemental composition of the clay fraction (f < 2 μm) with lateral resolution using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and with surface selectivity using X-ray photoelectron spectroscopy (XPS); (iii) the specific surface area (SSA) of fine earth and clay fractions by krypton physisorption. The SSA of the fine earth in illuvial horizons is predominantly due to finely divided Fe oxides, including goethite, characterized by an equivalent particle size of about 10 nm. Kaolinite platelets of about 2 μm size account for a large volume proportion in the clay fraction but have a minor contribution to SSA. Fe oxides and organic matter (OM) are intimately associated. Heterogeneity at the μm scale is created by local variations in the relative amounts of kaolinite and Fe-OM associations. These two kinds of physical entities are in random mixture. Moreover, variation of C/Fe atomic ratios reveals sub-μm scale heterogeneity. The latter is due to variation in the relative proportion of organic compounds and Fe oxides, indicating that aggregation of nanoparticles, and not only mere adsorption or pore filling, plays a role in these associations. In this regard, our results highlight that OM associated with Fe protects Fe oxides against physical displacement and that part of this associated OM is oxidizable by NaOCl treatment. These findings demonstrate that the concept of OM stabilization through association with Fe must be revisited when considering the sub-μm scale level because fine Fe oxide particles can be easily dispersed during oxidation of associated carbon. Combination of physical fractionation and micro-analysis (e.g. SEM-EDS, vibrational spectroscopy) offer promising perspectives to clarify the relationship between chemical composition and sub-μm scale architecture, and to better understand soil processes.