topography and soil, abiotic factors affecting crop 
growth, development and productivity

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 genetically-dictated characters are expressed in the plant.

Topography as Abiotic Factor

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.

Farms here differ in topographical features such as elevation, slope, and aspect, the direction that a crop area faces (example, north-facing)

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 as Abiotic Factor

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 Soil and Climatic 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 has distinct effects on plant growth and development, depending on natural adaptation.

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 or compactness 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.

Biological properties refer to the living organisms present in the soil including both beneficial microorganisms and pathogens. This last property though is treated under biotic rather than abiotic factors of the environment.

Click here to read the importance of microbes in improving agricultural productivity

By way of example, clayey or heavy soils have high water holding capacity and do not easily dry up than sandy or loose soils. However, the former, being compact, tend to have poor drainage and aeration. Soil pH, with values ranging from 0 to 14, dictates the availability of certain essential elements  to crop plants. Most crops are productive at pH levels near pH 7 which is the pH of  pure water (H₂O). The organic matter content of the soil is also important in assessing the capacity of the soil to make certain elements available to plants. Soils with plenty of humus, the end product of organic matter decomposition, tend to have high cation exchange capacity.

Plants Are Not Soil Eaters

Yes, plants are not soil eaters. There's no question about it, there's no more doubt about it. Indeed, it has already been established since a long time ago that this abiotic factor is not essential to plant growth and development and to crop productivity. Rather, it is the nutrient elements that are present in the soil as well as water and non-mineral elements from air that plants absorb. These make plants grow, enable them to complete their life cycles, and allow them to produce the yields that humans harvest.

REFERENCES

1. ABELLANOSA AL, PAVA HM. 1987. Introduction to Crop Science. CMU, Musuan, Bukidnon: Publications Office. p. 23-64.
2. EAGLEMAN JR. 1985. Meteorology: The Atmosphere in Action. Belmont, CA: Wadsworth Publishing Company. 394 p.
3. LANTICAN RM. 2001. The Science and Practice of Crop Production. college, Los Banos, Laguna, Phils.: SEAMEO SEARCA and UPLB. 330 p.
4. MILLER GT Jr. 2001. Environmental Science: Working With The Earth. 8th ed. Pacific Grove, CA, USA: Brooks/Cole. p. 135-167.
5. (PCARRD) PHILIPPINE COUNCIL FOR AGRICULTURE AND RESOURCES RESEARCH AND DEVELOPMENT. 1983. The Philippines Recommends for Coconut. 89 p.
6. WENT FW, THE EDITORS OF LIFE. 1963. The Plants. NY: Time Incorporated. p. 139-158.

(Ben G. Bareja 2011, edited Apr. 14, 2019)

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