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Thursday, January 31, 2013

Gardening Study School: Factors Affecting Plant Growth Outline

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
  1. Photosynthesis – The process of capturing light energy and converting it to sugar energy, in the presence of chlorophyll using carbon dioxide and water.
  2. Respiration – The process of metabolizing (burning) sugars to yield energy for growth, reproduction, and other life processes.
  3. 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)
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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