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🔗 Meteorology 🔗 Chemicals 🔗 Soil 🔗 Weather

Petrichor () is the earthy scent produced when rain falls on dry soil. The word is constructed from Greek petra (πέτρα), meaning "stone", and īchōr (ἰχώρ), the fluid that flows in the veins of the gods in Greek mythology.

🔗 Environment 🔗 Agriculture 🔗 Soil 🔗 Horticulture and Gardening

Hügelkultur (German pronunciation: [ˈhyːɡl̩kʊlˌtuːɐ̯]), literally mound bed or mound culture, is a horticultural technique where a mound constructed from decaying wood debris and other compostable biomass plant materials is later (or immediately) planted as a raised bed. Considered a permaculture practice, advocates claim that the technique helps to improve soil fertility, water retention, and soil warming, thus benefitting plants grown on or near such mounds.

🔗 Physics 🔗 Soil

The angle of repose, or critical angle of repose, of a granular material is the steepest angle of descent or dip relative to the horizontal plane to which a material can be piled without slumping. At this angle, the material on the slope face is on the verge of sliding. The angle of repose can range from 0° to 90°. The morphology of the material affects the angle of repose; smooth, rounded sand grains cannot be piled as steeply as can rough, interlocking sands. The angle of repose can also be affected by additions of solvents. If a small amount of water is able to bridge the gaps between particles, electrostatic attraction of the water to mineral surfaces will increase the angle of repose, and related quantities such as the soil strength.

When bulk granular materials are poured onto a horizontal surface, a conical pile will form. The internal angle between the surface of the pile and the horizontal surface is known as the angle of repose and is related to the density, surface area and shapes of the particles, and the coefficient of friction of the material. Material with a low angle of repose forms flatter piles than material with a high angle of repose.

The term has a related usage in mechanics, where it refers to the maximum angle at which an object can rest on an inclined plane without sliding down. This angle is equal to the arctangent of the coefficient of static friction μ_s between the surfaces.