土壤 (tǔ rǎng) is the formal, scientific term for 'soil' — the upper layer of earth in which plants grow. It consists of mineral particles, organic matter, water, air, and microorganisms. The character 土 means 'earth' or 'soil' and conveys the basic material; 壤 means 'loam' or 'fertile land', emphasizing texture and agricultural suitability. Together, they form a precise, technical compound used in ecology, agriculture, geology, and environmental science — not in casual speech.

This word appears frequently in academic texts, government reports on land conservation, and discussions about sustainable farming. Unlike the more general or colloquial 土 (tǔ), which can mean 'dirt', 'land', or even 'local/vernacular', 土壤 carries no informal or metaphorical meanings — it refers strictly to the physical, biologically active medium supporting plant life and ecosystem functions.