Vegetable Growers' Handbook Chapter III: Soils and Fertilizers

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Soil is a habitat for plants. As such, the soil's physical, chemical, and biological properties affect plant growth. The physical properties of a soil largely determine the ways in which it can be used. The size, shape, and arrangement of the primary soil particles are known as the physical properties of soil. Other important physical properties center on these such as the size and shape of the spaces between the particle arrangements, called the pore space, which has a direct effect on the movement of air and water, the ability of the soil to supply nutrients to plants, and the amount of water available to the plant.
The proportions of the four major components of soils, inorganic particles, organic materials, water, and air, can vary greatly from place to place and with depth. The amount of water and air in a soil can also fluctuate widely from season to season. However, the physical characteristics of the solid components, inorganic and organic particles, are essentially unchanging.
Chemical properties of soils are important in that, along with their physical and biological properties, they regulate the nutrient supplies to the plant. Without these nutrients supplied by the soil or applied as inorganic fertilizers, organically by manures, and other vegetative materials, plant growth would cease.
The biological properties of the soil are dictated by the macroorganisms and microorganisms. Good physical and chemical properties supply the right environment and sufficient nutrients to the organisms for optimal biological activity. This in turn improves the soil physical and chemical properties through improved structure and nutrient cycling.

V. A. Haby
Marvin L. Baker
Sam Feagley
Texas AgriLife Extension Service