The climatic Site factors
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The climatic factors factors include rainfall and water,light, temperature, relative humidity, air, andwind. They are abiotic components, includingtopography and soil, of the environmental factors that influence plant growth and development.
Rainfall and Water
Rainfall is the most common form of precipitation. It is the falling of water in droplets on the surface of the Earth from clouds. Other forms of precipitation are freezing rain, sleet or ice pellets, snowfall, and hail (Eagleman 1985; Miller 2001). The amount and regularity of rainfall vary with location and climate types and affect the dominance of certain types of vegetation as well as crop growth and yield.
Light
Light is a climatic factor that is essential in the production of chlorophyll and in photosynthesis, the process by which plants manufacture food in the form of sugar (carbohydrate). Other plant processes that are enhanced or inhibited by this climatic factor include stomatal movement, phototropism, photomorphogenesis, translocation, mineral absorption, and abscission
Light is that visible portion of the solar radiation or electromagnetic spectrum. It is a form of kinetic energy that comes from the sun in tiny particles called quanta or photons, travelling in waves.
Three properties of this climatic factor that affect plant growth and development are light quality, light intensity, and daylength or photoperiod. Light quality refers to the specific wavelengths of light; light intensity is the degree of brightness that a plant receives; and daylength is the duration of the day with respect to the night period.
Temperature
The degree of hotness or coldness of a substance is called temperature. It is commonly expressed in degree Celsius or centigrade (C) and degree Fahrenheit (F) . This climatic factor influences all plant growth processes such as photosynthesis, respiration,transpiration, breaking of seed dormancy, seed germination, protein synthesis, and translocation. At high temperatures the translocation of photosynthate is faster so that plants tend to mature earlier.
In general, plants survive within a temperature range of 0 to 50C The favorable or optimal day and night temperature range for plant growth and maximum yields varies among crop species.
Enzyme activity and the rate of most chemical reactions generally increase with rise in temperature. Up to a certain point, there is doubling of enzymatic reaction with every 10 C temperature increase. But at excessively high temperatures, denaturation of enzymes and other proteins occur.
Excessively low temperatures can also cause limiting effects on plant growth and development. For example, water absorption is inhibited when the soil temperature is low because water is more viscuous at low temperatures and less mobile, and the protoplasm is less permeable. At temperatures below the freezing point of water, there is change in the form of water from liquid to solid. The expansion of water as it solidifies in living cells causes the rupture of the cell walls
Air
The air is a mixture of gases in the atmosphere. About 75% of this air is found in the troposphere, the innermost layer of the atmosphere which extends about 17 km above sea level at the equator and about 8 km over the poles.
In addition, about 99% of the clean, dry air in the troposphere consists of 78% nitrogen and 21% oxygen. The remainder consists of argon (slightly less than 1%), carbon dioxide (0.036%), and traces of other gases.
The oxygen and carbon dioxide in the air are of particular importance to the physiology of plants. Oxygen is essential in respiration for the production of energy that is utilized in various growth and development processes. Carbon dioxide is a raw material in photosynthesis.
The air also consists of suspended particles of dust and chemical air pollutants such as carbon monoxide (CO), carbon dioxide (CO2), sulfur dioxide (SO2), sulfur trioxide (SO3), nitrogen oxides, methane (CH4), propane, chlorofluorocarbons (CFCs), solid particles of dust, soot, asbestos and lead, ozone and many more.
However, the composition of this climatic factor is susceptible of variation. Recently, there has been a hightenend alarm about the increase of carbon dioxide in the atmosphere.
Relative Humidity
The amount of water vapor that the air can hold depends on its temperature; warm air has the capacity to hold more water vapor than cold air. There is almost one-half reduction in the amount of water vapor that the air can hold for every 10 C drop in temperature.
Relative humidity (RH) is the amount of water vapor in the air, expressed as the proportion (in percent) of the maximum amount of water vapor it can hold at certain temperature. For example, an air having a relative humidity of 60% at 27 C temperature means that every kilogram of the air contains 60% of the maximum amount of water that it can hold at that temperature.
The amount of water vapor in the air ranges from 0.01% by volume at the frigid poles to 5% in the humid tropics. In relation to each other, high RH means that the air is moist while air with minimal content of moisture is described as dry air. Compared to dry air, moist air has a higher relative humidity with relatively large amounts of water vapor per unit volume of air.
The relative humidity affects the opening and closing of the stomata which regulates loss of water from the plant through transpiration as well as photosynthesis. A substantial understanding of this climatic factor is likewise important in plant propagation. Newly collected plant cuttings and bareroot seedlings are protected against dessication by enclosing them in a sealed plastic bag. The propagation chamber and plastic tent are also commonly used in propagating stem and leaf cuttings to ensure a condition with high relative humidity.
Wind as Climatic Factor
Air movement or wind is due to the existence of pressure gradient on a global or local scale caused by differences in heating. On a global scale it consists of the jet stream flow and movement of large air masses. On the local scale only a smaller quantity of air moves. Surface winds are lower and less turbulent at night due to the absence of solar heating (Eagleman 1985).
When air that is close to the ground cools, it contracts and the pressure rises; when it warms, it expands and loses pressure. Where both cold and warm air occur in proximity, as over a lake and its adjacent shore, the cold flows to the direction of the warm air or from high to low pressure area to correct the pressure imbalance. This also happens in tropical Asia but in a larger and more complex way, as the monsoon winds (Ripley and The Editors of Time-Life Books 1974).
This climatic factor serves as a vector of pollen from one flower to another thus aiding in the process of pollination. It is therefore essential in the development of fruit and seed from wind-pollinated flowers as in many grasses
Moderate winds favor gas exchanges, but strong winds can cause excessive water loss through transpiration as well as lodging or toppling of plants. When transpiration rate exceeds that of water absorption, partial or complete closure of the stomata may ensue which will restrict the diffusion of carbon dioxide into the leaves. As a result, there will be a decrease in the rate of photosynthesis
Microclimate is a local set of atmosphericconditions that differ from those in the surrounding areas, often with a slight difference but sometimes with a substantial one. The term may refer to areas as small as a few square meters or square feet (for example a garden bed or a cave) or as large as many square kilometers or square miles. Because climate is statistical, which implies spatial and temporal variation of the mean values of the describing parameters, within a region there can occur and persist over time sets of statistically distinct conditions, that is, microclimates. Microclimates can be found in most places.
Microclimates exist, for example, near bodies of water which may cool the local atmosphere, or in heavy urban areas wherebrick, concrete, and asphalt absorb the sun's energy, heat up, and re-radiate that heat to the ambient air: the resulting urban heat island is a kind of microclimate.
Bioclimate is (biology|meteorology) a climate, as it influences, and is influenced by, biological organisms.
Topographic Factor
Biotic Factors
Physical and Chemical Properties of Soil
Physical properties
1. Soil Separates and Soil Textures:
Mineral fraction of soil consists of particles of various sizes. According to their size, soil particles are grouped into the following types
The particle sizes of above groups are suggested by International Society of Soil Science. In India, international system of particle differentiation is commonly followed. The particle types are generally called ‘soil separates’ or ‘soil fractions’. Amount of soil separates is determined by a process known as mechanical analysis. In this process, soil sample is crushed and screened through a 2 mm round hole sieve. The screened soil is then homogeneously dispersed in water and allowed to settle.
2. Structure of Soil:
Sand, silt and clay are found in aggregated form. Arrangement of these soil particles on certain defined patterns is called soil structure. The natural aggregates of soil particles are clod peds whereas an artificially formed soil mass is called clod. Ped differs from fragment because the latter refers to the broken ped. Ped differs from concretion in the sense that the latter is formedinthe soil by precipitation of salts dissolved in percolating water.
Soil structure also reveals the colour, texture and chemical composition of soil aggregates. Soil structure is influenced by air moisture, organic matter, micro-organisms and root growth. When many particles or peds are aggregated into cluster, a compound particle is formed.
3. Density and Soil Weight:
Density of soil is the mass per unit volume. It is expressed in terms of gm per cubic centimeter. Average density of the soil is 2.65 gms per cubic centimeter. Density of soil varies greatly depending upon the degree of weathering.
Chemical properties
1. Inorganic Matters of Soil:
From the accounts given in the description of weathering process it is clear that compounds of aluminium, silicon, calcium, magnesium, iron, potassium and sodium are chief inorganic constituents of soils. Besides these, the soils also contain small quantities of several other inorganic compounds, such as those of boron, magnesium, copper, zinc, molybdenum, cobalt, iodine, fluorine etc. The amounts of these chemicals vary in soils of different places. Chemical composition of soil of one horizon differs greatly from the composition of soil in the other horizon.
2. Organic Matters in Soil:
Organic component of the soil consists of substances of organic origin; living and dead. In sandy soil of arid zone, it is found in very poor quantity (one or less than one per cent) but in peaty soil, it may be as high as 90%. When the plants and animals die, their dead remains are subjected to decomposition.
As a result of decomposition a number of different organic products or compounds are formed from the original residues. In the course of decomposition, the original materials are converted into dark coloured organic complexes, called humus. Sometimes living micro-organisms add sufficient amount of organic matters in soil in the form of metabolic wastes.
4. Coagulation or flocculation of colloidal particles:
Colloidal particles in the suspension can be coagulated either by heating or by adding some substances which contain opposite charged ions. When substances carrying positive ions are added in suspension containing negatively charged colloid particles, ions will move and accumulate on the surface of colloids carrying opposite charge. Finally a stage comes when colloidal particles cannot attract more opposite charged ions This is called isoelectric point As a result of ion accumulation on their surface, the colloids first become large and heavier and finally they tend to settle at the bottom in floccules. This process is known as flocculation.
5. Tyndal phenomenon:
Colloidal particles in suspension can be seen when a strong beam of light is passed through suspension and observer looks it from the place at right angle to the path of light. The colloidal particles become visible as strongly illuminated particles and they appear bigger than normal size. This phenomenon is known as “Tyndal effect”.
6. Brownian movement:
Colloidal particles when suspended in dispersion medium show a characteristic continuous zig-zag motion, called Brownian movement. This type of movement was first observed by English botanist Robert Brown, hence it is called Brownian movement. The movement is exhibited because of characteristic collision of one particle with others. This prevents the particles from settling down.
