EXTERNAL FACTOR
CLIMATIC FACTORS
AFFECTING GROWTH
The
climatic factors include water, light, temperature, relative humidity, air and
wind.
PRECIPITATION:
It
is the falling of water in droplets on the Earth from clouds. Other forms of
precipitation are freezing rain, sleet or ice pellets, snowfall, and hail
(Eagleman 1988, 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.
In crop agriculture, water is an
important climatic factor. It affects or determines plant growth and
development. Its availability, or scarcity, can mean a successful harvest, or
diminution in yield is increased from 1 to 2 but plant responses differ depending
on plant species. Most plant are mesophytes, that is, they are adapted to
conditions with moderate supply of water.
But
some, called hydrophytes, require watery or water – logged habitats while
others, called xerophytes, are more tolerant to dry conditions.
The resurrection plants are in fact
capable of surviving near complete desiccation. They are capable of losing 90%
or more of cellular water in their vegetative tissues and still remain alive.
They can remain dried and appear some dead for several years but when
rehydrated, suddenly spring back to life.
WATER:
Is
a substance with the unique property of being able to exist in three states:
(i) Liquid
(ii) Solid
(iii) Gas
As
a Liquid it is clear, colorless and odorless. In state of matter it has been described
as a fluid, a substance which flows freely without fixed shape. It melts and
freezes at Oo c (32o F) and boils at 100o c (212o F) under normal atmospheric pressure. Through
precipitation mainly rainfall, liquid water is made available to plants as
surface water, soil moisture, ore groundwater. It comprises about 70 – 90% of
the body or even more on fresh weight basis, although only a small fraction of
the water absorbed is utilized. Most of the absorbed water in plants is lost
through transpiration and only about I percent or less is used in the various
biochemical processes.
However,
the importance of water in plants can be negated in some cases. Water can
possibly cause unfavourable effects on plant growth and development. Excess
water in the soil can insure flood prone plants, like corn (maize), due to lack
of oxygen. In this case water stress due to flooding means oxygen stress by
deficiency (hypoxia) or total absence (anoxia) on the other hand, the injury
caused by acid rain indicates that purity and quantity relate to the importance
of water. With dissolved sulfuric acid and nitric acid that are formed in the
air from sulfur dioxide and nitric oxide generated by power plant, smelters,
other industrial plants, factories cars acid rain can seriously injure plant.
LIGHT:
Light
is a climatic factor that essential in the production of chlorophyll and in
photosynthesis the process by which plants manufacture food in the form of
sugar (carbohydrate). Other plants processed that are enhanced or inhibited by
this climatic factor include stomata movement, phototropism, photo
morphogenesis, translocation, mineral absorption, and abscission.
Light
is 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.
There
are three properties of light climatic factor that affect plant growth and
development are
(i) Light intensity
(ii) Light intensity
(iii) Day length or photoperiod
LIGHT QUALITY
This
refers to the specific wavelengths of light
LIGHT INTENSITY
Is
the degree of brightness of a plant receives
DAY LENGTH
Is
the duration of the day which respect to the night period
TEMPERATURE:
Is
the degree of hotness or coldness of a substance. 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
photosynthetic is faster so that plants tend to mature earlier.
In general, plant survive within a
temperature range is 0 to 50oc
enzyme activity and the rate of most chemical reactions generally increase with
the rise in temperature. Up to a certain point, there is doubling of enzymatic
reaction of 10oc
temperature increase.
But
at excessively high temperatures, denaturation of enzymes and other proteins
occur.
Excessively low temperatures can
also cause limiting affects on plant growth and development. For example, water
absorption is inhibited when the soil temperature is low because water is more
viscous at low temperature and less permeable. At temperature, the freezing
point of water, there is change in the form of water from liquid to solid. The
expansion of water at it solidifies in living cells causes the rupture of the
cells walls.
The
favourable or optimal day and night temperature range for plant growth and the
maximum yields varies among crop species.
According to McKinley (2005), orchid
plants are generally grouped into the following three temperatures and warm.
Orchids nee a day – night temperature difference of 10 – 15 F or about 5.55 –
8.34 c to flower. The exact temperature range are associated with these terms
vary, the flowing ranges being more common.
Cool
60 – 70 F or 15.55 – 21.11c (day), 50 – 55 F or 10 -12.77C (night) intermediate
70 – 80 F or 21.11 – 26.66 (day), 55 – 65 F or 26.66 – 32.22 C (day, 56.70 F or
18.33 – 21.11 C night.
AIR:
Is
a mixture of gases in the atmosphere. According to Miller (2001), about 75% of
this air is found in the troposphere the innermost layer of the atmosphere
which extends about 17km above sea level at the equator and about 8km over the
poles.
About
99% of the cleanly 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 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 lighten
and alarm about the increase of carbon dioxide in the atmosphere.
RELATIVE
HUMIDITY:
Is
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. According to
Eagleman, there is almost one – half reduction in the amount of water vapor
that the air can hold for every 100 drop in temperature.
Relative
Humidity (RH) is the amount of water vapor is 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
27c temperature means that every kilogram of the air contains 60% of the
maximum amount of water that it can hold at the 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 cutting and bareroot
seedlings are protected against desiccation by enclosing them in a sealed
plastic bag. The propagation chamber and plastic tent and also commonly used in
propagating stem and leaf cuttings to ensure a condition with high relative
humidity.
WIND:
Is
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.
When
air that close to the ground cools, it contracts and the pressure rises, when
it warms, it expands and loses pressure. When both cold and warm air occur in
proximinity, as over a lake and its adjacent shore, the cold flows to the
direction of the warm correct the pressure imbalance. This also happens n
tropical Asia but in a larger and more complex way, as the monsoon winds.
This
climatic factor serves as vestor 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 n many grasses.
Moderate
winds favor gas exchanges, but strong winds can cause excessive water loss
through transpiration as well as lodging or toppling of plant. when
transpiration rate excesses of water absorption, partial or complete closure of
the stomata may ensure which will restrict the diffusion of carbon dioxide into
the leaves. As a result, there will be a decrease in the rate of photosynthesis
growth and yield.
Each
of the above discussed climatic factors has been shown to produce limiting
effects on various growth processes. However, the various climatic factor
always operate together and interact with each other under natural conditions.
ADAPHIC FACTOR
AFFECT GROWTH
Adaphic
factor include topography and soil
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 of inclination of a land
inclination of a land n 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. It is know
that where a landscape serves as a barrier against the movement of pollen or
seed between two plant populations, the populations will begin to differ either
through mutation or genetic drift. However depending on the plant species and
their modes of dispersal, habitat fragmentation and their separation by
distance may not always become effective barriers.
Researcher
recently found that hummingbirds seem to be more effective than bees in
transferring pollen of penstemon from one mountain range to another across
large distance. The altitude or elevation of the sea surface influences plant
growth temperature effect.
SOIL:
The
word soil is derived from the Latin word Solum meaning earthy material in which
plant grow. The science which deals with the study of soil is called soil
science, pedology (pedos = earth) or edaphology (edaphos = soil).
The
process of formation of soil is called pedogenesis. A soil complex is formed of
5 categories of components namely mineral matter, organic matter or humus, soil
water, soil air, and living organisms. This quality of soil is due to its
fertility, texture, structure, organic content and air – water relationship.
SOIL PROFILE:
The vertical layered structure of
soil is called the soil profile. There are four main horizons in a soil profile.
O
– Horizon is the organic layer composed of deed organic residues.
A
– Horizon is the top soil, the upper most layer which contains roots.
B
– Horizon is the sub soil.
C
– Horizon is the less weathered parent.
The
organic matter in the soil is of two type:
1. Freshly dead and partially decomposed
plant and animal material called litter or detritus.
2. Colloidal, amorphous and dark coloured
humus.
SOIL HELPS IN:
·
Providing
water and mineral to the land plants.
·
It
act as a substratum for a variety of organisms like bacteria, fungi, many kinds
of animals and plants.
·
It
is the site for decomposition of plants and animals.
·
It
provides water, minerals and fossil fuels to man.
TYPES OF SOIL
(Clayed
Sand and Loamy) and it water retention aeration and mineral contents determine
the nature of plant and animals on the basis of these characters of soil, the
plants are divided into 5 ecological categories
·
Halophytes
– plants found on saline soil.
·
Psammophytes
– plants found on sandy soil.
·
Lithophytes
– plants found on rock surface
·
Chasmophtyes
- plants found in rock crevices
·
Oxylophytes
– plants found on acid soil.
The
ground dwelling animals which may be censorial (running) such as ostrich, rhea,
ungulates, wolves, cats, bears, hyaenas etc. salutatory (jumping) such as
rodents, rabbits, wallabies, kangaroos or gravipon – tal (heavy) such as
turtles armadillos, elephants etc, different kinds of soil for example, if the
soil is firm and hard, the large animals inhabiting the ecosystem tem tend to
have small hooves or paw. If the soil is wet and spongy, they tend to have
broad hooves or paws.
MINERALS
Minerals
are also called as biogenic materials and are essential for the proper growth
of plant and animals are determined by specific distribution of minerals.
Deficiency or absence or excess of minerals results in abnormal growth or even
death or organisms are adapted differently.
Examples:
A). Plants found in nitrogen – deficient bog
soil have either nitrogen fixing bacteria or become in sectivorous.
B). Snails occur in soils rich in calcium
content to form their shell.
C). Halophytes and many marine animals have
salt secreting glands.
D). Leguminous plants like pea, gram meth
show symbiosis with nitrogen fixing bacterial in their root nodules.
High
concentration of minerals generally limits the distribution of animals.
FIRE:
Fire
has important effects on the environment. Fire removes plant cover, burns
litter on the soil surface and causes loss of nutrients. Due to forest fires a
variety of animals groups die.
Range of
tolerance
Plants
and animals show a range of tolerance to environmental factors. The factor,
which is present in least amount may become limiting. For example water
availability limits plants growth in deserts.
But,
on only “to little” of something is a limiting factor, even “too much” may be
the limiting factor. The organisms and abundant in the central optimum range in
the zone of stress, only a few organism survive and in the zone of intolerance,
organisms are absent. If is organism has wide range of tolerance range is
narrow it is restricts.
BIOLOGICAL FACTOR
·
WEEDS
Weeds
are foreign plants i.e. they are plants net intend to be where they are.
Weeds
are a problem because they compete for the same soil and nutrients within it,
sunlight and water that are intended for those plants specifically placed in an
area within the garden. Some cause little harm but other more aggressive weeds
can destroy areas of a garden rapidly especially in the spring and early summer
months.
The
most common perennial garden weeds are.
- Dandelion
- Bindweeds
- Creeping butter cup
- Nettle
- Ground elder
- Horsetail
The most common annual garden weeds are
- Groundsel
- Bitter cress
As
with diseases weeds are difficult to eliminate and regulate maintenance is best
form of defense. The removal of weeds little or often will help prevent
establishment and spread and it is paramount not to let the weed develop to the
sede producing stage.
The application of anti weed material can also
help. By laying weed control fabric before planning a beed will provide a
defense wall a prohibit weeds and the use of mulches and /or chipped barks on
beds around plants will also provide a deterrent to weeds
PEST
Garden
pest can take many forms with insects, birds and animals all providing a threat
to health plant successful plant growth. Health plant tend to be resilient to
some pest damage but action should be out of control.
INSECTS
The
list of insect pests in the garden is extensive and includes wasps on fruits
aphids and whitefly on a whole range of plant. vine weevil are also a pest.
Removal of these insect is most effective when using nature reduce them. For
instance wasps can be lured to traps filled with sugary bait and the attraction
of birds into your garden will keep caterpillar numbers down, the introduction
of lady bird, lace wing and lover flies will all reduces the aphid population as will nematodes particularly in
war locations.
ANIMALS
A
whole variety of animal can be regarded as garden pests from the over exuberant
to the neighbors stray cats, each individual garden will have its own hit list
of animal problems. Cats can be deterred by using cat repellant using strong
scents where they tend to use the garden as a toilet. Citrus peel or moth ball
are recommend here. Wild animal such as deer or bulgers can also present a
problem. Badgers are protected and therefore be encouraged to explore other
areas and not your garden. Badgers have been known to destroy fences and
barriers to gain access to their usual foreign grounds so simply re fence the
area will not solve the problem.
DISEASE
When
dealing with all living things disease can always be present disease are caused
by either bacteria, virus or fungus and can have a devastating effect, even
killing plants in extreme cases when left untreated. Diseases can affect all
growing stages of plants and all areas of it from the roots to the flowers,
sometimes affecting the whole plant and sometimes just part of it.
INTERNAL FACTORS - GENETIC
FACTORS
The
basis of the genetic control of plant expression is the gene a carrier of
information that determines a biological characteristic of an organism and is
transmitted from parents to progeny upon reproduction.
The gene is composed of the
deoxyribonucleic acid (DNA) the chemical basis of heredity or transmission of
traits from parents to progeny. The DNA directs the synthesis of proteins,
particularly enzymes, by the plant. Each enzyme in turn catalyzes specific
biochemical reaction which leads to the formation of certain products. In order
for a biochemical reaction to proceed, a specific enzyme must be available.
The
genetic control of plant growth and development also has reference to the
chromosome. The genes are located at specific loci in the chromosome, those
cellular bodies within the uncleus which, under the microscope, appear as
coiled contracted threads or rod – like bodies at certain stage of mitosis. The
number as well as the size and shape of chromosomes, called karyotype, varies
from species to species.
The
chromosomes are considered the physical basis of heredity. They occur single in
haploid (1N) spores and gametes, in pairs (2N) in the diploid body (somatic)
cells, mother cells and the fertilized egg, in triplicates (3N) in the triploid
endosperm cells; and in multiple sets in the polyploidy cells.
The
diploid (2N) number of chromosomes in the body cells in humans is 46, 24 in
rice and tomato, 20 in corn, and 14 in garden pea. In 2005, Genome refers to
all the genes present in one complete haploid set of chromosomes or an
organism.
In
diploid organisms such as garden pea, the gene exist n two alternative forms
called alleles that are always found at
the same point or locus on homologous chromosomes (pair chromosomes). These
alternative genes are always denoted by letter symbols. For example, the
experiment conducted by Gregor Mendel on garden pea is illustrated by assigning
the capital letter “s” for the smooth character of seeds and the small letter
‘S’ for the wrinkled character.
The
credit for the formulation of the basis of genetic control goes to Gregor
Mendel he discovered that the genes are transmitted between generations in
uniform predictable fashion. He crossed strains true – breeding pea that offer
in seven of the alternative characters. It is now know that in pea the
inheritance of these observable characters, or phenotype is controlled by a genetic
constitution, organenotype consisting of a single gene pair.
The
entire genetic make – up determines whether an organism should be a plant, an
animal a fungus, a protest, or a mineral. This factor also determines whether a
plant should be a tree, a shrub, a herb, a vine, a liama, either a vascular or
a non vascular plant, a gymnosperm or an angiosperm, and down to the smallest
classification of a species, a variety alone or a strain.
REFERENCES
Rhodes,
1.970 competition between herbage grasses, herb. Abst 4;115 – 121
Goetz
. H.1969. composition and yield of native grassland sites fertilized at
different rates of nitrogen: Range manage. 27:384 – 390
Deltilis,
J.k M.I. Dyer and D.T winn 1979. Net photosynthesis root respiration and
regrowth of bouteloua gracile following stimulated grazing. Oecology 41;127 –
137
Davidson,
J.L and F.C mithorope. 19660 leaf growth in daclylis glumerate following
defliation annuals of botany 30;173 – 184.
Mastaler
2, J.W. 1977. The Green House Environment. John Wiley and Sons. Pp.629
RESEARCH INSTITUTE IN NIGERIA
1. Arable Crops Research Institutes
2. National Agricultural Extension
Research & Liaison Services (AERLS)
3. Institute of Agricultural Research
(IAR)
4. Institute of Agricultural Research and
Training (IART)
5. National Cereal Research Institute
(NCRI)
6. Lake Chad Research Institute (LCRI)
7. National Root Crops Research Institute
(NRCRI)
8. National Stored Products Research
Institute (NSPRI).
9. Forestry, Horticulture and Tree Crop
Research Institute
10. Forestry Research Institute of Nigeria
11. National Horticulture Research Institute
(NIHORT)
12. Cocoa Research Institute of Nigeria
(CRIN)
13. Nigeria Institute for oil palm Research
(NIFOR)
14. Rubber Research Institute of Nigeria
(RRIN)
15. Animal Production, Fisheries and
Oceanography Research Institute
16. National Animal Production Research
Institute (NAPRI)
17. National Institute for Freshwater
Fisheries Research (NIFFR)
18. Nigeria Institute for Oceanography and
Marine Research
19. Animal Health Research Institute
20. Nigeria Veterinary Research Institute
(NVRI)
21. Nigerian Institute for Trypansomiasis
Research (NITR)
22. International Institute for Tropical
Agriculture (IITA)
RESEARCH
AGAENCIES IN NIGERIA
1. Agricultural
Marketing Service (AMS)
2. Agricultural
Research Service (ARS)
3. Animal
and Plant Health Inspection Services (APHIS)
4. Centro
for Nutrient Policy and Promotion (CNPP)
5. Economics
Research Service (ERS)
6. Farm
Services Agency
7. Food
and Nutrition services (FNS)
8. Food
Safety and Inspection Service (FSIS)
9. Foreign
Agriculture Service (FAS)
10. Forest
Services (FS)
11. Gain Inspection Packers and Stockyards
Administration (GIPSA)
12. National
Agriculture Library (NAL)
13 National
Agricultural Statistics Service (NASS)
14. National
Resources Conservation Service (NRCS)
15. National
Institute of Food and Agriculture (NIFA)
16. Risk
Management Agency (RMA)
17. Rural
Development (RD)