Horticulture - Unit 4

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Horticulture - Unit 4

• Environmental Requirements for Good Plant Growth

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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.

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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
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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.

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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

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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.

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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

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• 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.

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Soil Improvement

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

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Drainage

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

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Moisture Retention

• Adding organic matter
• Mulch
• Irrigate
• Fertilize to add plant food

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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

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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

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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.

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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.

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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.

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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.

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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

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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.

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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

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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

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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

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Lime

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

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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

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The Environment Above the Ground

• Temperature
• Light
• Humidity
• Plant diseases
• Insects
• Gases or air particles

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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

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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.

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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.

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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.

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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.

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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.

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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)

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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.