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.