Sand fraction dominated by mineral quartz (SiO2) which is highly resistant to weathering processes, while the fraction of the dust is usually derived from mineral feldspar and mica are quickly obsolete, and at the time of weathering would release a number of nutrients, so textured soil dust are generally more fertile than soils sand. From this description shows that the fraction of sand and dust over the role physically, whereas most of the clay fraction size <1μm is an electrically charged colloidal particles or active as the anion or cation exchange, the clay fraction chemically bigger role than physically.
In determining the soil texture in the field with a sense method (by feel), then the sand fraction feel rough and not tacky, dust fraction will feel slightly soft and slightly sticky, but not slippery, while the fraction of the hat will feel smooth, sticky and slippery. Based on the results of laboratory analysis of the fractions making up ground, then according to the classification of the US Department of Agriculture (USDA) soil texture is divided into 12 classes as shown in Figure 1.6.
Based on the above image texture triangle, then a land called textured sand if it contains a minimum of 85% sand, textured dust when the dust content of at least 80%, and if it has a textured loamy clay fraction of at least 40%. In general, ideal berkomposisi soil composed of sand fraction from 22.5 to 52.5%, 30-50% and 10-30% dust fraction clay fractions or so-called textured clay.
Figure 1.6. Diagram USDA soil texture classes triangle
Based on the soil texture class is classified into three groups, namely:
1. Land textured rough or sandy soil means soil that contains a minimum of 70% sand. Soil texture classes including coarse textured soils there are 3 types is the texture of sand (sand), sand argillaceous texture (loamy sand) and sandy loam (sandy loam).
2. Soil fine textured or clayey soil means soil that contains a minimum of 37.5% clay fraction. Soil texture classes including fine-textured soils there are 3 types of clay soils (clay), dusty clay (silty clay) and sandy clay (sandy clay). 3. Soil textured or ground argillaceous, consisting of:
a) Soil texture was a bit rough but there are two types include textured sandy loam soil (sandy loam) or fine sandy loam,
b) Land textured there are 4 types of cover which is very smooth textured sandy loam, clay (loam), dusty clay (silty loam) or dust (silt), and
c) Soil finely textured but rather there are three types of cover clayey loam (clay loam), sandy clay loam (sand clay loam) or dusty clay loam (sandy silt loam).