CommunicateThese master horizons may then be further annotated to give additional information about the horizon. The International Union of Soil Sciences has developed a system called the World Reference Base, which has 32 Reference Soil Groups ().
#Living earth soil series#
system, called Soil Taxonomy (/technical/classification/taxonomy/), groups soils into 12 broad orders at the most general level, and more than 19,000 soil series at the most detailed level (Ahrens & Arnold 1999). Soil scientists capture this vast diversity through systems of soil classification.
DiverseThe variety of soil formation processes operating on different parent materials under different climatic, topographic, and biological conditions over varying periods of time gives rise to the vast diversity of soils on earth.
Soil scientists have learned to predict the current stage of these processes if given five key pieces of information about the soil's history - the five factors of soil formation - climate, organisms, topography, parent material, and time (Jenny 1941). Horizons form, minerals and rocks weather, nutrients leach, and plant communities change. Soils change over time through a host of biological, chemical, and physical processes. New soils are born with every landslide, volcanic eruption, or glacial retreat. The oldest soils on earth may be in Australia, where stable land forms have allowed some soils to age several million years. Young to Very, Very OldIt can be difficult to say exactly when some soils were born, but we can say that while some are young, many are very old. Soil colors range from the common browns, yellows, reds, grays, whites, and blacks to rare soil colors such as greens and blues. Soil organic matter is plant, animal, and microbial residues in various states of decomposition it is a critical ingredient - in fact the percentage of soil organic matter in a soil is among the best indicators of agricultural soil quality () (Figure 3). The most common mineral in soils is quartz it makes beautiful crystals but it is not very reactive. For example, a clay mineral called smectite can shrink and swell so much upon wetting and drying (Figure 2) that it can knock over buildings. Soil minerals are divided into three size classes - clay, silt, and sand (Figure 1) the percentages of particles in these size classes is called soil texture. Soil is a material composed of five ingredients - minerals, soil organic matter, living organisms, gas, and water. The improved conservation and management of soils is among the great challenges and opportunities we face in the 21st century. They are critical ecosystem service providers for the sustenance of humanity. Soils are dynamic and diverse natural systems that lie at the interface between earth, air, water, and life.
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