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Soil texture
Soil texture is a qualitative classification tool used in both the field and laboratory to determine classes for agricultural soils based on their physical texture. The classes are distinguished in the field by the "textural feel" which can be further clarified by separating the relative proportions of sand, silt and clay using grading sieves: The Particle-size distribution (PSD). The class is then used to determine crop suitability and to approximate the soils responses to environmental and management conditions such as drought or calcium (lime) requirements. A qualitative rather than a quantitative tool it is a fast, simple and effective means to assess a soil's physical characteristics. Although the U.S.D.A. system uses 12 classes while the UK-ADAS uses just 11, the systems are mutually compatible as shown in the combined soil textural triangle below.
==Field assessment using a hand texture chart==
Hand analysis, while an arbitrary technique, is an extremely simple and effective means to rapidly assess and classify a soil's physical condition. Correctly executed, the procedure allows for rapid and frequent assessment of soil characteristics with little or no equipment. It is thus an extremely useful tool for identifying spatial variation both within and between plots (fields) as well as identifying progressive changes and boundaries between soil classes and orders.
The method involves taking a small sample of soil, sufficient to roll into a ball of approx 2.5 cm diameter, from just below the surface. Using a small drop of water or 'spit' the sample is then moistened to the sticky point (the point at which it begins to adhere to the finger). The ball is then molded to determine its workability and its class according to the steps in the chart opposite.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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