Soil physical characteristics are a necessary part of a soil's quality assessment, and have direct and indirect effects on crop production and environment. The quality of a soil is a combination of inherent and dynamic soil properties, which include soil texture, depth to bedrock, types of clay, CEC, and drainage class. Soil structure can have a profound effect on many other properties, as it is the shape and arrangement of soil particles into aggregates. Aggregated soil types are generally the most desirable for plant growth. The soil characteristics such as form, soil density, soil color, consistence, and pore space describe the unique physical properties of the soil. Soil colloids are most important in soil fractions due to their properties, which make them contribute most to the physical and chemical activity taking place in soil. Texture (the content of sand, silt, and clay) and the presence of impervious layers such as clay pan determines the permeability of a soil. Soil compaction destroys the quality of the soil because it restricts rooting depth and decreases pore size. Soil resistivity is a measure of a soil's ability to retard the conduction of an electric current. Soil temperature controls the microbiological activity and growth of plants.