Soil Horizons

Soil horizons are distinct layers of soil that form naturally in undisturbed soil over time. The formation of soil horizons is called soil geomorphology and the types of horizons are indicative of the soil order. Like other natural processes, the age of the horizon increases with depth.

The reason why it’s useful to have a soil sensor in each horizon is because different horizons have different hydrological properties. Some horizons will have high hydraulic conductivities and thus have greater and more rapid fluctuations in soil moisture. Some horizons will have greater bulk densities with lower effective porosities and thus have lower saturation values. Some horizons will have clay films that will retain water at field capacity longer than other soil horizons.

Knowledge of the soil horizons in combination with an accurate soil sensor will allow the user to construct a more complete picture of the movement of water in the soil. The horizons that exist near the surface can be 6 to 40 cm in thickness. In general, with increasing depth, the clay content increases, the organic matter decreases and the base saturation increases. Soil horizons can be identified by color, texture, structure, pH and the visible appearance of clay films.

O: Surface layers Decaying plants on or near surface
A: Topsoil Organic & rich soil
B: Subsoil
  • Most diverse horizon
  • Horizon with the most sub classifications
C: Weathered Rock Aged parent material
R: Bedrock

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