Loam is soil containing 40-40-20% sand, silt, and clay by weight. Particle size ranges from >63 micrometres to <2 micrometres. USDA defines loam as soil not predominantly sand, silt, or clay
Soil science studies soil as natural resource on Earth's surface. Main branches are pedology (formation, chemistry) and edaphology (soil-living interactions). Soil occupies pedosphere, one of Earth's spheres. Soil scientists collaborate with engineers, agronomists, and other disciplines
Topsoil is the upper layer of soil containing highest organic matter concentration. Extends to 5-10 inches depth and holds water and air. Contains high concentration of roots for plant nutrient acquisition. Hosts significant bacterial, fungal and entomological activity
Surface roughness is the quality of a surface not being smooth. Measured by deviations of normal vector from ideal form. Can be measured using profilometers with contact or optical methods
Humus is dark organic matter formed from plant and animal decomposition. Contains nutrients, especially nitrogen, with C:N ratio between 8:1 and 15:1. Has amorphous structure lacking cellular organization. Composed of lignin, polyphenols, proteins, and carbohydrates
Porosity equals pore volume divided by total volume. Soil particle density is assumed to be 2.66 g/(cm³). Porosity can be expressed as (1 - bulk density) divided by particle density