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FACTORS OF PLANT GROWTH

The soil can be viewed as a mixture of mineral and organic particles of

varying size and composition in regard to plant growth. The particles occupy

about 50 percent of the soil's volume. The remaining soil volume, about 50

percent, is pore space, composed of pores of varying shapes and sizes. The pore

spaces contain air and water and serve as channels for the movement of air and

water. Pore spaces are used as runways for small animals and are avenues for the

extension and growth of roots. Roots anchored in soil support plants and roots

absorb water and nutrients. For good plant growth, the root-soil environment

should be free of inhibitory factors. The three essential things that plants absorb

from the soil and use are:(1) waterthat is mainly evaporated from plant leaves,

(2) nutrients for nutrition, and (3) oxygen for root respiration.

Support for Plants

One of the most obvious functions of soil is to provide supportfor plants.

Roots anchored in soil enable growing plants to remain upright. Plants grown by

hydroponics (in liquid nutrient culture) are commonly supported on a wire

framework. Plants growing in water are supported by the buoyancy of the water.

Some very sandy soils that are droughty and infertile provide plants with little else

than support. Such soils, however, produce high-yielding crops when fertilized

and frequently irrigated. There are soils in which the impenetrable nature of the

subsoil, or the presence of water- saturated soil close to the soil surface, cause

shall low rooting. Shallow-rooted trees are easily blown over by wind, resulting inwind throw.

Essential Nutrient Elements

Plants need certain essential nutrient elements to complete their life cycle.

No other element can completely substitute for these elements. At least 16

elements are currently considered essential for the growth of most vascular plants.

Carbon, hydrogen, and oxygen are combined in photosynthetic reactions and are

obtained from air and water. These three elements compose 90 percent or more of1

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the dry matter of plants. The remaining 13 elements are obtained largely from the

soil. Nitrogen (N), phosphorus (P), potassium (K), calcium Ca), magnesium (Mg),

and sulfur (S) are required in relatively large amounts and are referred to as the

macronutrients. Elements required in considerably smaller amount are called the

micronutrients. They include boron (B), chlorine (Cl), copper (Cu), iron (Fe),

manganese (Mn), molybdenum (Mo), and zinc (Zn). Cobalt (Co) is a micronutrient

that is needed by only some plants. Plants deficient in an essential element tend to

exhibit symptoms that are unique for that element.

More than 40 other elements have been found in plants. Some plants

accumulate elements that are not essential but increase growth or quality.

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