Q. Which soil horizon is commonly referred to as 'Humus'?
Answer: O Horizon
Notes: The 'O Horizon', also known as the organic horizon, is the topmost layer of soil that contains decomposed organic matter and is hence referred to as 'Humus'. This layer is critical in the soil ecosystem as it contributes nutrients and promotes microbial activity. The 'A' and 'B' Horizons, although important in their respects, do not contain as much organic matter and therefore are not considered to be the 'Humus' layer.