Kids Research Express

Soil, surface layer of the earth, composed of fine rock material disintegrated by geological processes; and humus, the organic remains of decomposed vegetation. In agriculture, soil is the medium that supports crop plants, both physically and biologically. Soil may be from a few inches to several feet thick. Components and Structure The inorganic fraction of soil may include various sizes and shapes of rocks and minerals; in order of increasing size these are termed clay, silt, sand, gravel, and stone. Coarser soils have lower capacity to retain organic plant nutrients, gases, and water, which are essential for plants. Soils with higher clay content, which tend to retain these substances, are therefore usually better suited for agriculture. In most soils, clay and organic particles aggregate into plates, blocks, prisms, or granules. The arrangement of particles, known as soil structure, largely determines the soil's pore space and density, which translates into its capacity to ho

Healthy soil is indispensable for a healthy garden. Plants derive water, oxygen for their roots, and essential nutrients from the soil. Soil consists of two components: minerals from weathered rocks and organic matter from decayed organisms and animal wastes. The mineral content of the soil provides plants with nutrients, such as calcium, potassium, and phosphorus. Organic matter improves drainage and helps prevent waterlogged soils, reducing the occurrence of diseases such as root rot. Soil texture, the size of the individual soil particles, affects how fast water drains and how well plants absorb nutrients. The largest soil particles are grains of sand . Sand grains fit loosely together with large gaps between them, resembling marbles in a jar. The large pores let water (and the nutrients dissolved in it) drain out too quickly for most plants to absorb it. Clay particles, on the other hand, are very tiny, and they pack closely together, resembling tiny beads in a jar. The pores bet