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Horticulture - Unit 4

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Horticulture - Unit 4 Environmental Requirements for Good Plant Growth The Plant Environment In order to grow properly, plants require a certain environment. – PowerPoint PPT presentation

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Title: Horticulture - Unit 4


1
Horticulture - Unit 4
  • Environmental Requirements for Good Plant Growth

2
The Plant Environment
  • In order to grow properly, plants require a
    certain environment.
  • This environment is divided into two parts
  • The underground in which roots grow and live.
  • The aboveground in which the plant visibly exits.

3
The Underground Environment
  • Rhizoshere The 24 inches of soil just below the
    earths surface.
  • Soil is made up of sand, silt, clay, organic
    matter, and pore spaces which hold air and water.

Air Liquid 50 Water 25 Air 25
Solid portion 50 Mineral Matter
45 Organic Matter 5
4
Soil
  • Soils are classified according to the percentage
    of sand, silt, and clay they contain.
  • Soil particles vary greatly in size. A sand
    particle is much larger than silt. Clay
    particles are by far the smallest.
  • Clay particles hold water and food elements much
    more effectively than larger particles.
  • A certain amount of clay in all soil is important
    for this reason.

5
Soil continued
  • Soils also vary greatly in general composition.
  • Some soils are formed from rock breaking down,
    others are formed as certain materials are
    deposited by water.
  • A normal soil profile consists of three layers
  • Topsoil-the depth normally plowed or tilled
  • Subsoil-a well defined layer under topsoil
  • Soil bedrock or lower subsoil

6
The Ideal Soil
  • The ideal soil is about 50 solid material.
  • The solid matter is mainly minerals and a small
    portion of organic matter.
  • The other 50 is pore space.
  • The pores are small holes between solid matter
    and are filled with water and air in varying
    amounts.
  • Ideal water/air ratio is half and half
  • The amount of water and air depends on the soil
    structure and type of soil.
  • Sandy soils have large pores and water is lost
    quicker (these are called well-drained soils)
  • If soils contain too much clay, they may not
    drain well enough to allow enough oxygen in pore
    space.

7
Types of Water in Soil
  • Gravitational Water that is unable to hold
    against the force of gravity. It is and becomes
    part of ground water. It is of little use to the
    plant because it drains away taking soluble plant
    food elements with it.
  • Capillary water Is held against the force of
    gravity. It is held in the small pores of the
    soil. There are three types
  • Free moving Moves in all directions
  • Available or field capacity Water left after
    capillary movement stops - Roots move toward it.
  • Unavailable Held tightly and can only be moved
    as vapor

8
  • Sandy Soil Sandy or light soils include soils
    in which clay or silt make up less than 20 of
    the material by weight. These soils drain well,
    but have little capacity to hold moisture and
    plant food.
  • Clayey Soil Must contain at least 30 clay. It
    is a heavy soil which has poor drainage and
    aeration capacities. Clayey soils tend to hold
    too much moisture.
  • Loamy soils The most desirable for general use.
    It is a mixture of equal parts of sand, silt and
    clay.

9
Soil Improvement
  • Soils may be improved by adding increased
    drainage, irrigation methods and organic matter
    and plant food.

10
Drainage
  • Add organic matter
  • Use of tile drains to remove water from the soil
  • Raising plant beds
  • Place ditches between planting beds

11
Moisture Retention
  • Adding organic matter
  • Mulch
  • Irrigate
  • Fertilize to add plant food

12
Disease control
  • Use resistant varieties of crops
  • Use chemicals sparingly
  • Pasteurize soil used in container
    gardening Soil or sand should be heated
    thoroughly for 30 minutes at 180 degrees F

13
Nutritional Deficiencies
  • Nutritional or plant food deficiencies often
    show up on the leaves.
  • Yellow or pale green indicates a nitrogen
    deficiency.
  • Purple color on the underside, shows a phosphorus
    deficiency.
  • By the time these symptoms appear, damage has
    already been done.
  • A soil test would have determined the plants
    needs

14
Advantages and disadvantages of planting media
mixes.
  • Advantages
  • Mix is uniform
  • Mixes are sterile
  • Soil less mixes lighter in weight therefore
    easier to handle
  • Good moisture retention and drainage are possible
    through the proper combination
  • Disadvantages
  • Since they are light, the containers may be blown
    over
  • Mineral content is low - Minor plant food
    elements may be missing
  • Plants may hesitate to extend roots when
    transplanted to soils.

15
Content of Mixes
  • Perlite a gray-white material of volcanic
    origin. Used to improve aeration.
  • Sphagnum moss the dehydrated remains of acid
    bog plants, used in shredded form. Used for
    covering seed because it has good moisture
    retention.
  • Peat moss Partially decomposed vegetation that
    has been preserved underwater. High moisture
    holding capacity.
  • Vermiculite Very light, expanded material with
    a neutral pH. Has a very high moisture-holding
    capacity.
  • Limestone Ground natural limestone.
  • Tree bark usually the bark of pine or oak trees
    broken into small pieces.
  • Slow releasing fertilizers Contain plant food
    which is gradually made available to plants.

16
Plant Food and Fertilizers
  • Water is the most important plant food. It makes
    up 90 of the weight of plants.
  • Water is the most limiting factor of plant
    growth.
  • All food elements are dissolved in water and move
    into the plant in a soluble form.
  • Only approx. 1 of the water absorbed is used by
    the plant.
  • 99 is lost through the process of transpiration.

17
Transpiration
  • Transpiration of water is high when soils are wet
    and the stomata open wide to allow more water to
    escape.
  • It is estimated that there are 250,000 stomata
    in 1 square inch of the underside of an apple
    leaf.
  • For each 10 degree increase in temperature C, the
    loss of water is doubled.
  • A single corn plant can use 2 quarts of water per
    day.
  • Stomata open in response to light.
  • Transpiration is of little use. The cooling is
    minimal.

18
Plant Food Elements
  • Minor Elements
  • Required in smaller amounts
  • calcium
  • magnesium
  • sulfur
  • iron
  • manganese
  • boron
  • copper
  • zinc
  • Major Elements
  • Required in large amounts
  • nitrogen
  • phosphorus
  • potassium

19
Nitrogen
  • Encourages above ground vegetation growth and
    gives a dark green color to leaves.
  • Produces soft, tender growth
  • Seems to regulate the use of other major
    elements.
  • Too much nitrogen may lower plants resistance to
    disease, weaken the stem, lower the quality of
    fruit, and delay maturity or hardness of tissue.

20
Phosphorus
  • Encourages plant cell division
  • Flowers and seeds will not form without it
  • Hastens maturity
  • Encourages root growth and strong roots
  • Makes potassium more available
  • Increases plants resistance to disease
  • Improves the quality of grain, root and fruit
    crops

21
Phosphorus
  • TOO MUCH
  • Increases soluble salt which can dry out roots by
    pulling water from the roots
  • TOO LITTLE
  • Purple coloring on underside of leaves
  • Reduced flower, seed and fruit production
  • Susceptible to cold injury
  • Susceptible to disease
  • Poor quality fruit and seeds

22
Potassium
  • Rarely available in sufficient amounts
  • Encourages resistance to disease
  • Encourages strong roots
  • Essential for starch formation
  • Necessary for chlorophyll development
  • Essential for tuber development
  • Encourages efficient use of carbon dioxide

23
Lime
  • Acts as plant food
  • Affects soil acidity
  • Furnishes calcium which is important in formation
    of plant cell walls.

24
Soil Acidity (pH)
  • Most plants grow best in pH from 5.6 to 7
  • Soil at 7 is neither acid or alkaline (basic)
  • Values lower than 7 indicate acid soils
  • Above 7 indicate alkaline soils
  • To lower acidity, use materials such as sulfur,
    iron sulfate or aluminum sulfate
  • To increase acidity, apply lime

25
The Environment Above the Ground
  • Temperature
  • Light
  • Humidity
  • Plant diseases
  • Insects
  • Gases or air particles

26
Temperature
  • The temperature of the air has one of the
    strongest effects on plant growth
  • Some plants such as lettuce, cabbage and kale
    grow best in cool temperatures
  • Corn, beans and tomatoes prefer hot weather
  • Generally, plant growth increases up to a
    temperature of about 90 degrees

27
Light
  • Light must be present before a plant can
    manufacture food.
  • Some plants prefer full sunlight, others prefer
    shade
  • Light also affects plants other ways. Thr
    response to different periods of day and night is
    called photoperiodism.

28
Photoperiodism
  • Definition The response of plants to different
    periods of light and darkness in terms of
    flowering and reproductive cycles.
  • Short Day Flower only when days are short and
    nights are long. (chrysanthemum and Christmas
    Cactus)
  • Long Day Flower when days are long and nights
    are short. (lettuce and radishes)
  • Indifferent Plants that do not depend on
    periods of light to flower.

29
Other Reactions to Light
  • Plants grow toward their source of light because
    the plant stem produces more growth hormones on
    the shady side.
  • Dehlias develop fibrous root systems during long
    days but develop thick storage organs when days
    shorten.

30
Humidity
  • The moisture level in the air
  • Most plants are not affected greatly by minor
    changes
  • When humidity is very high (80-100), problems
    such as the spread of fungal disease may occur.

31
Plant Diseases and Insects
  • Any time a plants is suffering for disease or
    insect damage, production will suffer.
  • Leaf damage reduces ability to produce food
  • Stem damage may girdle (circle) or clog up a stem
    and kill the entire plant.

32
Gases and Air Particles
  • Carbon dioxide is vital for plant growth
  • Greenhouse operators find that adding carbon
    dioxide to the air increased growth to plants
    more than enough to pay for it
  • Some air pollutants cause damage to the plant
    (Sulfur dioxide from coal furnaces and carbon
    monoxide from cars)

33
Student Activities
  • Bring in one jar 1/2 full of soil. Add water to
    2 inches from top. Replace lid and shake well.
    Next class, examine layers. Classify soil
    according to texture triangle.
  • Examine label on plant food. List all plant food
    elements and record the percentage of each.
    Identify major and minor elements.
  • Using a soil test kits, test a sample for pH
    level, phosphorus and potassium.
  • Complete self-evaluation.
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