New Global Soil Database

A new database on the world’s soils improves knowledge of the current and future land productivity as well as the present carbon storage and carbon sequestration potential of the world’s soils. It helps to identify land and water limitations, and assist in assessing the risks of land degradation, particularly soil erosion risks, said FAO today.

Derived from the soil database, FAO has produced a global Carbon Gap Map that allows for the identification of areas where soil carbon storage is greatest and the physical potential for billions of tons of additional carbon to be sequestrated in degraded soils.

Soil information has often been the one missing information layer, the absence of which has added to the uncertainties of predicting the potential for and constraints to food and fibre production as well as the capacity of soils to hold carbon and to act as a sink.

Until now, most efforts to use agriculture to manage greenhouse gases have involved above-ground sequestration, primarily through planting trees, since the amount of carbon that can be sequestered in this way is substantial. However, there is also growing interest in finding ways to increase carbon sequestration in soils. Soils are presumed to be the largest carbon reservoir of the terrestrial carbon cycle, although estimates of their magnitude vary widely. Soil can be a source or a sink for green house gases depending on land use management. For long-term sequestration, organic carbon must be stored in forms and in locations in the soil profile with slow turnover.

“The chemical and physical properties of soils also help to determine specific information about how well a soil will perform as a filter of wastes, as a home to organisms, as a location for buildings and as pool for carbon. The more information we have about soil properties, the more we can evaluate the quality of our natural resources all over the world and their potential to produce food now and in future scenarios of climate change” said Alexander Muller, FAO Assistant Director General for Natural Resources and Environment Management.

“Soil characterization data are a key piece of the picture of how an ecosystem work,” said Freddy Nachtergaele, FAO soil expert. “Soil properties also tell us whether the soil has the potential to store enough water to keep plants growing through a drought or to withstand a flood. Farmers’ knowledge of soil properties also forms the basis of managing fertilizer application efficiently thus reducing avoidable nutrient losses to the environment.”

Land Potential Assessment

FAO and the International Institute for Applied Systems Analysis combined recent regional and national updates of soil information worldwide and incorporated the FAO-UNESCO Soil Map of the World into a new Harmonized World Soil Database (HWSD). Other partners such as The European Soil Bureau Network; the Institute of Soil Science of the Chinese Academy of Sciences and ISRIC World Soils contributed significantly to the information.

Soils as carbon stores

Different soils have different capacities to act as a store for carbon which has direct implications for capturing greenhouse gases. The world's soils hold more organic carbon (1500 Gt) than the atmosphere that contains about half this amount as CO2 (720 Gt), and the vegetation (600 Gt) combined. Thus, relatively small changes in the flow of carbon into or out of soils have significant effect on a global scale. In addition to predicting the effect of changing rainfall patterns under climate change scenarios, scientists require information on soil moisture storage capacities which are provided by this database.

The HWSD provides improved soil information worldwide particularly needed in the context of the Climate Change Convention and post Kyoto Protocol instruments for soil carbon measurements and carbon trading. It can also be used by agronomists, farm experts and scientists in planning the sustainable development of agricultural production and will improve land degradation assessments, environmental impact studies and sustainable land management options.

The database will also serve to guide policies aimed at addressing land competition issues concerning food, energy and biodiversity.

***www.fao.org

Behaviour of Plastics and Elastomers

The relationship between wear and surface hardness obtained for metals would predict a comparatively poor behavior for polymers. However, their special structural features give rise to properties that can play a special role in wear.

The viscoelastic deformation behavior is characterized by time-, temperature- and velocity-dependent deformation processes. Relatively low levels of hardness and strength, high plasticity, low thermal conductivity, and high thermal expansion are effects of the weak secondary bonding forces between the macromolecules and their coiled structures. In particular, the low tendency to adhesion gives polymers their good slip characteristics with steels as the sliding partners — in the absence of additional abrasive particles — because of the low frictional forces involved, and the slip system is characterized by additional emergency running properties. Polyamide and PTFE occupy the prime positions here as they possess good cohesive linkage properties compared with other unreinforced polymers.

If abrasive sliding stress is present, the dependence on hardness known for metals cannot really be depicted in the same way. It has been demonstrated that polymers exhibit a good relationship between wear resistance and crack propagation energy, or even between wear and the product of tensile strength and fracture strain.

Due to their material properties, polymers have proved successful where streams of small particles cause impact stress in addition to sliding wear, i.e., with abrasive impact wear and with erosive attack. Although polymers generally have poor resistance to abrasive sliding attack, their ductility, especially of elastomers, leads to a behavior superior to that of metals when the impacting component is dominant. Their behavior therefore differs significantly depending on the angle of impact. The material becomes heated due to internal friction, which can lead to complete failure at high jet intensities.

The preferred elastomers include the polyurethanes and synthetic rubbers because of their outstanding resistance to wear. In polyurethanes, greater resistance is found in the hardness range 70 – 95 Shore A, whereas normal grades of rubber reach their optimum between 50 and 70 Shore A. It is not possible to separate the influencing factors systematically with respect to tribological behavior because of the large number of additives, types of rubber, and applications.

If, for rubber and C 60 H steel, the amount of wear relative to St 37 steel is plotted versus the impact angle and the hardness of the jet material then, it is possible to show the very different wear behavior of these two materials.

Abrasion and Erosion - An Introduction

Practical experience with industrial equipment, machinery, and plant has shown that components have only limited service lives. Damage and ultimate failure of the component can occur as a result of changes in the material that originate at the surface, even if the components are designed such that long-term action of the forces alone causes neither fracture nor undue deformation.

If the reactions responsible for the damage are of electrochemical or predominantly chemical nature, the term corrosion is normally used, whereas mechanical damage to the surface of the component is defined as wear.

Attempts to avoid a loss of material due to wear, or at least to reduce the loss, concentrate on making the affected surface more resistant to wear. This can be achieved by mechanical, thermal, or thermochemical treatment of the surface or by applying or depositing metallic coatings.

Under some circumstances the wear conditions can be changed by design measures so that the danger for the affected component surface is eliminated or reduced to a tolerable level.

With few exceptions (e.g., running-in of bearings), wear in engineering means an undesired change that causes very high costs every year; in a highly developed, industrialized country this can amount to ca. 1 – 2 % of the gross national product [1].

Excluding the contribution from the automobile sector, the proportions occurring in the various branches of industry can be divided up approximately as shown in Table (1). From this, it can be seen that the plant construction typical of the chemical industry plays an insignificant role, and wear is correctly known as "the problem child of mechanical engineering" [2].

Wear, friction, and lubrication are described under the term tribology as the science of the study, industrial application, and modification of the phenomena and processes occurring between surfaces which are acting against each other and moving relative to one another; this includes boundary surface interactions between solids, and between solids and their gaseous or liquid surroundings.

Since at least two components of a system are involved in wear, it is not a pure material characteristic, but only a system characteristic. Wear itself is generally understood as progressive loss of material from the surface of a solid body caused by mechanical action, i.e., contact and relative motion with a solid, liquid, or gaseous phase.

[1] BMFT-Report: Damit Rost und Verschleiß nicht Milliarden fressen, BMFT, Bonn 1984.
[2] B Genath

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