Soil: Formation, Composition and Importance | 土壤：形成、组成与重要性

📚 Soil: Formation, Composition and Importance | 土壤：形成、组成与重要性

Soil is one of the most familiar materials on Earth, yet it is often misunderstood. In KS3 chemistry, soil is studied as a natural mixture whose properties depend on the rocks and organic materials it contains.

土壤是地球上最常见的物质之一，却常常被误解。在KS3化学中，土壤被当作一种天然混合物来研究，其性质取决于其中所含的岩石和有机物质。

Understanding soil helps us see how chemical weathering, particle size, water and pH all connect in the environment.

理解土壤有助于我们认识化学风化、颗粒大小、水和pH如何在环境中相互联系。

1. What Is Soil? | 什么是土壤？

Soil is the loose, weathered layer of material that covers much of the Earth’s land surface. It is not a single substance but a mixture of weathered rock, minerals, decaying organic matter, water, air and living organisms.

土壤是覆盖在地球大部分陆地表面的松散风化层。它不是单一物质，而是风化岩石、矿物质、腐烂有机质、水、空气和生物的混合物。

Because the parts of soil are not chemically combined, they can be separated by physical methods. A handful of soil from a garden may contain pieces of rock, plant roots, tiny shell fragments and water.

由于土壤的各组分不是化学结合，因此可以用物理方法将它们分开。从花园里抓起的一把土壤可能含有岩石碎块、植物根、细小的贝壳碎片和水分。

2. Soil Composition: Four Main Parts | 土壤的组成：四个主要部分

A typical fertile soil has roughly 45% mineral matter, 25% water, 25% air and 5% organic matter. These proportions vary greatly. Sandy soil has more air and less water, while clay soil can hold more water but less air.

典型的肥沃土壤大约由45%的矿物质、25%的水、25%的空气和5%的有机质组成。这些比例变化很大。砂质土壤空气更多、水分较少，而黏质土壤能保持更多水分，但空气较少。

The four main components can be remembered as: mineral particles, organic matter, water and air.

四个主要组分可以记为：矿物质颗粒、有机质、水和空气。

• Mineral particles come from broken rock and provide structure.
• Organic matter comes from dead plants and animals and provides nutrients.
• Water dissolves minerals and carries them to plant roots.
• Air supplies oxygen for root respiration and soil organisms.

• 矿物质颗粒来自破碎的岩石，构成土壤骨架。
• 有机质来自死去的动植物，提供养分。
• 水溶解矿物质，并把它们输送到植物根部。
• 空气为根呼吸和土壤生物提供氧气。

3. Mineral Particles: Sand, Silt and Clay | 矿物质颗粒：砂、粉砂和黏土

Mineral particles are classified by size. Sand particles have diameters between 0.05 mm and 2 mm. Silt particles are between 0.002 mm and 0.05 mm. Clay particles are smaller than 0.002 mm.

矿物质颗粒按大小分类。砂粒的直径在0.05毫米至2毫米之间。粉砂颗粒在0.002毫米至0.05毫米之间。黏土颗粒小于0.002毫米。

Sand feels gritty and drains water rapidly. Silt feels smooth and floury. Clay feels sticky when wet, holds water tightly and swells. The mixture of sand, silt and clay determines the soil texture.

砂摸起来有砂砾感，排水很快。粉砂摸起来光滑如面粉。黏土湿时黏稠，紧紧保持水分并会膨胀。砂、粉砂和黏土的混合比例决定了土壤质地。

A loam soil has a balanced texture. It contains enough sand for drainage, enough clay to retain moisture, and enough silt to make it workable. Most crops grow well in loam.

壤土具有均衡的质地。它含有足够的砂以保证排水，足够的黏土以保持水分，以及足够的粉砂使其易于耕作。大多数作物在壤土中生长良好。

4. Humus: The Organic Matter | 腐殖质：有机质

Humus is the dark, spongy organic component of soil. It forms when dead leaves, roots, animals and other once-living matter are broken down by decomposers such as bacteria, fungi, earthworms and woodlice.

腐殖质是土壤中深色、海绵状的有机成分。它由枯叶、根、动物和其他曾具有生命的物质在细菌、真菌、蚯蚓和潮虫等分解者的作用下分解而形成。

Humus is not fully decayed; it is a stable mixture of complex organic compounds. It holds water, improves soil structure and acts as a slow-release store of nutrients such as nitrogen and phosphorus.

腐殖质并未完全腐烂；它是复杂有机化合物的稳定混合物。

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