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| Lettuce covered in frost looking decidedly other worldly. Want to bet it's growth was slowed in this situation? |
A. Growth defined
The progressive
development of an organism; an irreversible increase in volume due to
the division and enlargement of of cells. The processes of growth,
including the three major functions that are basic to plant growth
and development
- Photosynthesis – The process of capturing light energy and converting it to sugar energy, in the presence of chlorophyll using carbon dioxide and water.
- Respiration – The process of metabolizing (burning) sugars to yield energy for growth, reproduction, and other life processes.
- Transpiration – The loss of water vapor through the stomata of leaves.
There are two sets of
of factors that affect plant growth: Environmental and Genetic
Each can be a limiting
factor in plant growth. These environmental factors do not act
independently example - inverse relationship between soil moisture
and air
B.
Environmental Factors
1. Light –
variations, intensity, duration
The
nature of light
Light
changes through the seasons
Quality,
intensity and duration of light are important
1. Quality can't
be controlled on a field scale - Feasible on specialty crops
2. Intensity of
light (brightness) is an important factor.
photosynthesis
light intensity
3. Duration -
Photoperiodism - Plant behavior in relation to day length
-
long day plants - flower only if days are longer than same critical
period - 12 hours Grains and clovers
-
short day plants - flower only if days are shorter than a critical
period soybeans.
-
indeterminate - flower over a wide range of day lengths. Tomato,
cotton, buckwheat
Plants
compete with other plants for available light, nutrients and water –
weeds are invariably plants that can out compete our preferred
plants. Weeds grow faster, taller blocking out light or can access
water and or nutrients better than our desired plants; that's why we
remove them.
2.
Water/Moisture
Availability
and lack of water effects
Wilting
point and permanent wilting point
Water
and roots
Water
and leaves
Water
in the xylem and phloem
Plant
growth restricted by low and high levels of soil moisture
1.
can be regulated with drainage and irrigation
2.
good soil moisture improves nutrient uptake
If
moisture is a limiting factor fertilizer is not used efficiently.
3.
Temperature
Metabolic
changes
Nutrients
in cold/warm soils
Most
plant growth occurs in a fairly narrow
range - 60 - 100 degrees F
1.
Temperature directly affects
photosynthesis
(slows)
respiration
transpiration -
loss of water
absorption
of water and nutrients
2.
The rate of these processes increases with an increase in
temperature responses are different with different crops
cotton
vs collards or potatoes
fescue
vs bermuda grass
These
generalizations hold within a crops range of adaptation
3.
Temperature also affects soil organisms: nitrifying bacteria
inhibited by low temperature. pH may decrease in summer due to
activities of microorganisms
4.
Soil temperature affects water and nutrient uptake
High
temperatures cause increased respiration sometimes above the rate of
photosynthesis. This means that the products of photosynthesis are
being used more rapidly than they are being produced. For growth
to be sustained photosynthesis must be greater than respiration.
4.
Atmospheric conditions; effects of pollution
Carbon
dioxide makes up 0.03 per cent of air by volume. Photosynthesis
converts carbon dioxide to organic material in the plant.
Carbon dioxide is returned to atmosphere by respiration and
decomposition
In a corn field or closed
greenhouse CO2 level may drop and become a limiting factor in
growth.
Increasing CO2 can
increase crop yields respiration of plants and animals -
decomposition of manure or plant residue may release CO2
Adding it to a greenhouse
at very high concentrations for several hours will eliminate pests.
greenhouse crops
Plant growth and quality
can be enhanced by supplemental CO2. Growth responses have been shown
with tomatoes, lettuce, cucumbers, flower crops, greens, peas, beans,
potatoes
Air Quality
Air pollutants in
sufficient quantities are toxic to plants sulfur dioxide - provides
sulfur at low levels
Acid rain – acidifies
water has demonstrably killed trees
Thinning ozone –
permits ultraviolet radiation harming plant growth especially in
seedlings UV radiation is intimately tied with genetic mutations
Particulate matter in
atmosphere reduces photosynthesis and clogs stomata on plant leaves
also inhibiting photosynthesis
5. Nutrients
the
18 nutrients
Nutrients
from the atmosphere:
Carbon,
hydrogen and oxygen
Primary
nutrients:
Nitrogen,
Phosphorous, Potassium (NPK)
Minor
nutrients - they are minor only in that not that much is required by
the plant, still all are essential to plant growth
Calcium,
Magnesium, Iron, Boron, Manganese, Copper, Sulphur, Molybdenum, Zinc,
Choline
Justus
von Liebig (a German chemist) considered the father of modern
chemical agriculture
Leibig
gave us NPK – the three primary minerals for plant growth
Liebig's
Law of the Minimum
How
plants take up nutrients
Most
of the nutrients used by the plants are absorbed by the roots from a
soil solution
Nutrients
in the soil
Nutrients
in the plant
Over
fertilizing causes burning and leaves; possible collapse (death) of
the plant and is a principle cause of polluted ground water.
Furthermore the lush growth promoted by over fertilizing is
delightful eating for most insect pests.
C.
Genetic Factors (Heredity)
Yield
potential is determined by genes of the plant.
Characteristics such as quality, disease resistance, drought
hardiness are determined by the genetic makeup.
Ornamental
plants
- not interested in total growth as much as appearance
control
over the genetic factor by his choice of variety.
Field
crops - highest yielding, disease resistant, etc.
Nursery
- Best appearance - dwarf vs larger shrubs
Inheritance
in plants
F1
generation and beyond
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