Search

The soil’s position in the material cycle of the lithosphere (Fig. 2.1) shows that a large number of processes are involved in the formation of rocks, lithogenesis, in the form of a cycle. At the beginning of lithogenesis, rocks are formed through crystallization when the molten magma cools down. They are subject to further diverse changes through the processes of weathering, erosion, transport, deposition, diagenesis, metamorphism and anatexis, which are connected to one another in a cycle. Soils are a significant station in this cycle. On the one hand, they are the result of the transformation of rock in contact with the atmosphere, hydrosphere and biosphere (pedogenesis), and on the other, they deliver material for the formation of new rocks. For this reason, soils cannot be understood and classified without knowledge of the rocks; however, the same is true for many rocks without knowledge of the soils (Kittrick 1985).

In most topsoils, the mass of the soil organic matter only amounts to a few percent, but has an important influence on all soil functions and plays a central role in the global carbon cycle. For this reason, the carbon content, or the dark color value, is a differentiating criterion for soil descriptions in German and international classifications.

Many regulating functions of soils (Sect. 1.2) are based on biogeochemical processes, and are therefore affected by soil chemical properties. Examples are the storage and supply of nutrients, the sorption and degradation of contaminants, as well as the buffering of acid deposition. The chemical processes taking place at biogeochemical interfaces are of outstanding importance. About 40–60 % of the soil volume consists of pores, which can be filled with water (soil solution) or gases (soil air), depending on the actual soil moisture. The soil solids mainly consist of minerals and smaller fractions of organic matter. This porous system of mineral and organic soil particles, gases, aqueous solutions and organisms leads to the formation of very large and chemically reactive interfaces. These interfaces can adsorb, complex, precipitate or chemically transform various ions and molecules. This chapter provides an introduction to the chemical properties and processes regulating the behavior of nutrients and contaminants in soils.

All soils on our planet are useful. They serve the ecological balance, plant and animal production or various uses of civilization (cf. Sect. 1.2). The larger the population of our Earth, the more different uses are competing for one and the same soil. This is why the following fundamental question is being raised more and more frequently: Is this soil suitable for a specific use? This question is as old as human interactions with soils. Already in the Stone Age, people had to ask themselves whether it would be profitable to clear the forest and convert it for agricultural purposes. The beginnings of soil classification are also rooted in the suitability of soils (cf. Chap. 7). The most important assessment is still the question of soil fertility or yield potential of soils for different crops. This is best portrayed in Roman and Greek literature, with the coincidence of the classification of soils and their suitability for use.

Soils are the biologically active part of the outermost layer of the Earth’s crust, ranging in thickness from a few centimeters to several decameters. The Earth’s crust, in turn, generally has a thickness of 5–40 km and is part of the lithosphere, which has an average thickness of approx. 100 km and consists of the tectonic plates with the continents. The total distance between the ground surface to the Earth’s center is of 6370 km. These orders of magnitude illustrate how soils form a thin and fragile skin on the Earth’s surface, requiring special care.

Soils are the natural sites for all terrestrial plants, developing roots in the soil space that anchor them in the soil, and absorbing water, oxygen and nutrients from the soil through their root system. This requires good rootability and distance to bedrock (Sect. 9.1). Furthermore, soils must be able to store sufficient plant available water (Sect. 9.2), provide enough gas exchange (Sects. 6.5 and 9.3) and thermal fluxes (Sects. 6.6 and 9.4), and also contain large enough quantities of available plant nutrients (Sect. 9.5). These properties are significantly determined by the thickness of the rootable soil zone. Because fertile soils are the basis for supplying a growing human population with food and because arable soils are a limited good, they must be protected from damage and destruction, in order to preservetheir fertility and to prevent famine among the population. Their capacity to produce any kind of yield is called soil fertility or productivity (Chap. 11).

Soil genesis is the study of the development of soils. Soil is a natural body, developing from rock at the Earth’s surface through pedogenic processes (weathering and mineral formation, decomposition and humification, structure formation and various substance translocations) under a specific climate, specific litter-delivering vegetation, and population of soil organisms.

Soils, as a part of ecosystems, fulfill a series of functions for human beings and the environment. These include habitat, utilization, transformer, filtering, buffering, and archive functions (see Chap. 1). They are potentially endangered by human activities. On the one hand, these include chemical contaminations such as industrial emissions, spreading of sludges, dredged material and physical soil degradation including soil erosion, soil compaction or excavations.

Soils are natural entities and as such, each soil is characterized by typical physical properties, with color (Sect. 6.8) and texture (Sect. 6.1) being the most readily visible. Therefore, they are important components of any soil description.

Boden sind Naturkorper und als solche durch jeweils typische physikalische Eigenschaften gekennzeichnet; Farbe (Kap. 6.8) und Kornung (Kap. 6.1) fallen am meisten ins Auge. Sie sind daher wichtige Bestandteile einer jeden Bodenbeschreibung.

Although much progress has been achieved in revealing more about the chemical structure of soil organic N and P and the mechanisms involved in their formation, we are still far from completely knowing the structures and understanding the formation and dynamics of these major soil organic matter components.

Kohlenstoffbilanzierungen und Untersuchungen zur Humusbildung sind darauf angewiesen, pedogene organi sche Substanz zu quantifizieren und zu charakterisieren. Oftmals kommt es in anthropogenen Boden zu einer Beteiligung von kohlenstoffhaltigen Materialien aus industriellen Prozessen, wie Z. B. Kahle oder Rus, so das die Charakterisierung und Quantifizierung der im Laufe der Bodenentwieklung akkumulierten rezenten organischen Substanz erschwert wird. Ein Beispiel sind die forstlich rekultivierten Kippenboden des Lausitzer Braunkohlenreviers. Hier liegen Braunkohle (geogener Kohlenstoff) und Humus (pedogener Kohlenstoff) in Mischung vor und lassen sich weder makromorphologisch noch mit einfachen chemischen Parametern unterscheiden. Der Kohlegehalt sollte jedoch aus bodenokologischer Sicht bei der Beschreibung des Gehaltes organischer Substanz von den Zersetzungsprodukten organischer Pflanzenreste unterschieden werden (AG Boden 1994), weil Kohle aufgrund ihrer grosen Oberflache das Bindungsvermogen eines Bodens fur Wasser und organische Schadstoffe verandern und bodenchemische Parameter, wie Sulfitgehalt und pH, beeinflussen kann.