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The abiotic factors that affect plant growth and development include topography, soil, and climatic factors. They are the nonliving components of the environment which, along with the biotic or living factors, determine the extent in which the genetic factor is expressed in the plant.
Topography is a nonliving factor that refers to the “lay of the land.” It includes the physical features of the earth such as the land elevation, slope, terrain (flat, rolling, hilly, etc.), mountain ranges and bodies of water.
The slope or inclination of a land is the percentage change in its elevation over a certain distance. It is measured by dividing the vertical distance from the foot to the top of the land by the horizontal distance between those points, multiplied by 100. A 45-degree angle of elevation is equivalent to 100% slope.
The steepness of a slope affects plant growth through differential incidence of solar radiation, wind velocity and soil type. A steep slope is susceptible of rapid surface runoff and soil erosion which cause soil degradation.
The altitude or elevation of the land with respect to the level of the sea surface influences plant growth and development primarily through temperature effect. The relationship of this abiotic factor to temperature is like that of distance from the equator to the arctic poles. According to Stiling (1999), temperature decreases by 1 C for every 100 m increase in altitude in dry air.
This abiotic factor is an important consideration in crop or site selection for more productive crop farming. Coconut prefers an elevation not exceeding 600 meters above sea level (masl) (PCARRD 1982); for better quality, tea is best grown above 1000 masl while rubber requires not more than 500 masl because at higher elevation latex flow is restricted (Abellanosa and Pava 1987); the seasonality of ripening of various fruit crops, e.g. durian , is modified when they are planted in different elevations.
The effect of land elevation on plant growth and development is apparent when exploring a high-rise mountain. Dominance of certain plant types varies with elevation. With change in height from sea level to 16,000 feet (4,876.8 meters) from the foot to the top of a mountain in the Peruvian Andes or New Guinea, temperatures change from tropical to subtropical, temperate, and subarctic to arctic.
Likewise, the influence of this abiotic factor on plant growth and distribution is noticeable. There is a change from tropical vegetation at the coastal base to the oak forest, then conifers, and finally a tundra-like scene with hardy grasses, mosses and dwarf shrubs. At the arctic top, only occasional lichens are found on exposed rocks.
In the tropics, the timber line above which no more tree grows may be found between 13,000 to 14,000 feet above sea level or 3,962-4,267 masl (Went and The Editors of Life 1963).
Soil
is the outermost layer of the surface of the earth in which plants
grow. It is composed of eroded rock, mineral nutrients, decaying plant
and animal matter, water and air. This abiotic factor is likewise
important in crop farming and is treated under the heading Soil and Climatic Adaptation or Requirement of crops.
Most plants are terrestrial in that they are anchored to the soil through their roots, with which they absorb water and nutrients. But epiphytes and floating hydrophytes
do not need soil to live. Variation in the physical, chemical, and
biological properties of the soil have distinct effects on plant growth
and development, depending on
natural adaptation.
There are two properties of the soil having pronounced direct effects on plant growth and crop production: physical and chemical properties. There are also biological factors
or living organisms in the soil such as the earthworms, insects,
nematodes and microorganisms like bacteria, fungi, actinomycetes, algae,
and protozoa. These organisms help in improving soil structure, tilth,
aeration, water permeability and soil nutrient availability.
The physical and chemical properties of the soil are referred to as edaphic factors of the plant environment. The physical properties include the soil texture, soil structure, and bulk density which affect the capacity of the soil to retain and supply water while the chemical properties consist of the soil pH and cation exchange capacity (CEC) which determine its capacity to supply nutrients.
It is now known that this abiotic factor (soil) is not essential to plant growth. Rather, it is the nutrient elements that are present in the soil that make plants grow and enable them to complete their life cycle.
REFERENCES
(Ben G. Bareja, January 2011)
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