1 requirements for good plant growth. 2 underground environment rhizosphere –the 24 inches of soil...
TRANSCRIPT
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Requirements for Good Plant Growth
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Underground Environment• Rhizosphere
– The 24 inches of soil just below the earth’s surface.
– Unlocking the secrets of this area of the soil could result in the development of better crops.
• Salt tolerant, Higher yields, Use less fert and chemical.
– It is only recently that we have had tools to study the rhizosphere and the inter action of what goes on there.
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Underground Environment
• Medium– Soil or soil substitute in which plants are
grown.– This is a very important factor.– Plural of medium is media or mediums.
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Soil• Soil is made up of:
– Sand, Silt, Clay, Organic Matter, Living organisms, and pore spaces which hold water and air.
– 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 is much larger than a silt
particle.
• Clay particles are by far the smallest.
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Soil
• Clay particles hold moisture and plant food elements much more effectively than larger particles.
• A certain amount of clay in all soil is important for this reason.
• Soils vary greatly in composition.– Some were formed as a result of rock breaking
down over thousands of years.– Others were developed as materials were
deposited by water.
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Soil
• The normal soil profile consists of three layers.– 1. The topsoil
• This represents the depth normally plowed or tilled.• Contains the most organic matter or decaying plant
parts.
– 2. The subsoil• Well defined layer immediately below the topsoil.• If a soil is well drained, the roots will penetrate
deeper into the subsoil since oxygen is available at greater depths.
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Soil– 3. Soil bedrock, or lower subsoil.
• Natural structures of the soil is more important to:– Outdoor Gardeners, Fruit growers, and nursery
workers who plant outside.
• Workers who grow plants in containers can add ingredients to the soil to change its:– Structure, moisture holding ability, drainage
ability, or fertility.– Most container plants are grown in completely
soil less mixes.
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Soil
• An ideal soil is about 50% solid material.– This solid material consists mainly of
minerals and a small percentage of organic matter.
• The other 50% of the ideal soil is pore space.
– These pores are small holes between soil particles and are filled w/ water and air in varying amount.
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Soil– After rain or irrigation, the pores may be nearly
filled with water and the air is pushed out.– As the soil dries, the amount of water decreases
and the pores gradually fill with air again.– The ideal water to air ratio in the pores is about
half and half, 50% air and 50% water.– The amount of moisture and air the soil will
hold depends on the soil structure and type of soil.
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Soil– Sandy soils with large particles also have more
pore spaces. Water is lost more quickly from these large pores as the force of gravity drains the water out.
– These are called well drained soils.– As the clay content of these soils increases,
more water is held.– If soils contain too much clay, they may not
drain well enough to allow enough oxygen in the pore space for good plant growth.
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Water in Soil
• Types of water in soil:– Gravitational water
• Is water that the soil is unable to hold against the force of gravity.
• It becomes part of the groundwater or drains away into streams.
• It is of little value to the plant since it drains away quickly, carrying soluble plant food with it.
– Soils with larger pores lose water faster to the force of gravity than do soils with smaller pore spaces.
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Water in Soil
– Capillary water• Is held against the force of gravity.
• It is held in the small pore spaces of the soil and as a thin film of water around soil particles.
• There are three types of capillary water.– Free moving capillary water
» Moves in all direction in soil just as it does in a glass capillary tube.
» Soil must be saturated at low levels for water to continue to move upward in field soil.
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Water in Soil– Available capillary water or field capacity
» Water left after capillary movement stops.» The soil surface is now dry.» Any water held is as a thin film around soil
particles.» Water does not continue to move through the
soil at this point.» This is the most important water for plants.
– Unavailable capillary water» It is not available to plants.» It can only be moved as vapor.» Soil this dry is called air dry because under
normal conditions no more moisture will move.
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Types of Soil• Sandy Soil
– Include soils in which silt and clay 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– A soil must contain at least 20 % clay.– They are known as heavy soils.– Relatively poor drainage and aeration capabilities.– They also hold fertilizer and plant food, which can be
beneficial to plant growth.
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Types of Soil
• Loamy Soil– This is the most desirable soil for general use.– Loam is a mixture of approximately equal parts
of sand, silt, and clay.– If it has more sand than silt or clay it is known
as a sandy loam, more clay, clayey loam, more silt, silty loam.
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Soil Improvement
• Soils used for outdoor plant growth may be improved through increased drainage, irrigation, and the addition of organic matter.
• Since it would be very expensive to change the % of sand, silt, and clay in the soil to improve the soils drainage, aeration, or moisture holding capacity. Other practices must be used.
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Soil Improvement
• Drainage and aeration can be improved by changing the soil structure.– One way this is done is by adding organic
matter to encourage earthworms.– Their tunnels and castings result in better soil
structure through aggregation.• The clinging together of soil particles in large crumb
like shapes.
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Soil Improvement
– Lime and gypsum (calcium sulfate) also aid in soil aggregation and improve structure in some cases.
– Another method is the use of tile drains to remove water from the soil.
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Soil Improvement
• Moisture Retention– Adding OM improves the water holding
capacity of soils.– OM hold many times its own weight in water,
for example peat moss holds 15X its weight in water.
– OM also holds plant food effectively and allows the slow release of the food for plant use.
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Soil Improvement
• Mulches– Such as compost, wood chips, or bark, are
placed on the surface of the soil to help retain soil moisture by reducing runoff.
– Mulches also help keep the soil cool, thus reducing evaporation loss.
– Beyond these practices, the grower ahs little control over the soil structure or its moisture content.
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Nutritional Deficiencies
• Nutritional deficiencies often show up on the leaves of plants.– Yellow or pale green leaves indicate a N
deficiency.– P deficiency shows up as a purple color on the
underside of the leaf.• By the time these symptoms appear, damage has
already been done to the plant.
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Soil Pests• Soils harbor certain diseases such as root rot
and wilt.• Nematodes, which are tiny animals, and
insects may also damage roots.• Resistant varieties of crops or natural
controls such as crop rotation must be used to control these problems.
• Chemicals are sometimes used as a last resort
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Soil Pests
• Soil pasteurization is needed any time soil or sand is used for container growing.
• Soil or sand should be heated thoroughly to 180 F for 30 minutes before mixing with other materials.
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Planting Media Mixes
• More and more growers are using planting mixes that contain little, if any, soil.
• Advantages– The mix is uniform, it doesn’t vary in fertility,
acidity, or texture.– The mixes are sterile.– Soiless mixes are lighter in weight, thus easier
to handle and ship.
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Planting Media Mixes
• Disadvantages:– Since they are lightweight, containers kept
outdoors may blow over.– Mineral content is usually low, trace plant food
elements to plant life may be missing.– Plants transplanted from mixes to soils often
hesitate to extend roots into such a different growing medium.
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Planting Media Mixes
• Content of mixes:– Perlite: A gray-white material of volcanic
origin. Used to improve aeration of the media.– Sphagnum moss: Is dehydrated remains of acid
bog plants, used in shredded form for seeds. Has excellent moisture hold capabilities.
– Peat moss: Is partially decomposed vegetation that has been preserved underwater.
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Planting Media Mixes
– Vermiculite: Is a very light expanded material with a neutral pH. It has a very high moisture-holding capacity.
– Limestone: Refers to ground natural limestone. It is also known calcium carbonate. It tends to raise pH.
– Tree bark: Usually the bark of pine or oak trees broken into small pieces and used in planting mixes. Fine pine bark is now used extensively in container growing.
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Planting Media Mixes
– Slow release fertilizers: Are fertilizers containing plant food which is gradually made available to plants over a period of time.
• Mixes may contain two or more of these ingredients.
• Soiless mixes may be used as soil conditioners by digging them into the soil in varying amounts.
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Plant Food and Fertilizers
• Plants may be grown grown in soil, soilless mixes, or a combination of the two.
• Plant food must be readily available to the plant.
• Fertilizers must be added as the plant requires food and the plant food elements must be in a water soluble form.
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Plant Food and Fertilizers
• Water is the most important plant food element.
• It makes up nearly 90% of the weight of plants and is the most limiting factor in plant growth.
• All plant food elements are dissolved in water and move into and throughout the plant in a water solution.
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Plant Food and Fertilizers• Only about 1% of the water absorbed is
actually used by the plant.
• The other 99% is lost through transpiration.
• As leaf temperature rises the more water lost through transpiration.
• For each 10 C increase in temperature, the loss in doubled.
• A single corn plant can transpire 2 qts of water/day.
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Plant Food and Fertilizers• Transpiration is of little value to the plant.
• It cools the leaf slightly, but air movement and heat radiation are most important in leaf cooling.
• Plant food may be divided into two groups:
• Major elements– Nitrogen, phosphorus, and potassium
• Minor elements– Calcium, magnesium, sulfur, iron, manganese, etc…
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Plant Food and Fertilizers• Elements are listed as major and minor according
to the relative amounts of each element needed for good plant growth.
• Commercial fertilizers and plant foods show the % or pounds per hundred weight of the three major elements in large numbers on the bag or container.
• If the fertilizer analysis has the numbers 5-10-5 on the label, the mix is 5% nitrogen 10% phosphorus and 5% potassium.
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Plant Food and Fertilizers
• The other 80% is filler material which makes it easier to spread the plant food evenly.
• Just as humans require balanced diets, plants need a balanced of food for best growth.
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Plant Food and Fertilizers• Nitrogen
– Nitrogen is purchased in one of four forms.– Nitrate of soda NaNO3
• Which is highly soluble and quickly available. It also tends to lower soil acidity. It contains 16% N.
– Ammonium Nitrate NH4NO3
• Is not as soluble and available over a longer period of time. It contains 33% N.
– Ammonium Sulfate (NH4)2SO4
• Becomes available more slowly and leaves the soil more acidic. It is good for plants that grow well in very acidic. It contains 21% N.
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Plant Food and Fertilizers
– Urea Formaldehyde• Is an organic for of N and is more slowly available than
the inorganic forms. It contains 38% N.
– Of the three major plant food elements, N has the most noticeable effect on plants.
– N encourages aboveground vegetation growth and gives a dark green color to the leaves.
– Because the addition of N quickly produces a visible effect, there is often a tendency to overuse it.
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Plant Food and Fertilizers
• Too much N may:– Lower the plants resistance to disease.– Weaken the stem because of long soft growth.– Lower the quality of fruits, causing them to be
too soft to ship.– Delay maturity of hardness of tissue and thus
increase winter damage to plants.
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Plant Food and Fertilizers
• Not enough N results in a plant being:– Yellowing or light green in color.– Stunted in root and top growth.
• N is lost from the soil very easily by leaching. It is very soluble in water and is not held by the soil particles because of the charges of the particles involved.
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Plant Food and Fertilizers
• Phosphorus– Superphosphate 20% P– Treble superphosphate 46% P– Rock phosphate 25-35% P– Ammonium phosphate 48% P– Phosphorus is present to some extent in all soils.– Unlike N it is held tightly by soil particles and
therefore is not easily leached from the soil.
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Plant Food and Fertilizers
– Because it may not be in the water soluble form, it is usually not available to to plants in the amount needed.
• Phosphorus affects plants in several ways:– It encourages plant cell division.– Flowers and seeds don’t form w/out it.– It hastens maturity, thereby offsetting the quick
growth caused by N.
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Plant Food and Fertilizers
– It encourages root growth and the development of strong root systems.
– It makes potash more easily available.– It increases the plants resistance to disease.– It improves the quality of grain, root, and fruit
crops.
• Insufficient phosphorus results in:– Purple coloring on the undersurface of the leaves.
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Plant Food and Fertilizers
– Reduced flower, fruit, and seed production.– Susceptibility to cold injury.– Susceptibility to plant diseases.– Poor quality fruits and seeds.
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Plant Food and Fertilizers
• Potassium– The most common sources of potassium are:
• Muriate of potash 60% K• Sulfate of potash 49% K• Nitrate of potash 44% K and 13% N
– K is rarely present in the soil in sufficient amounts to harm plants.
– It tends to modify both the fast, soft growth of N and the early maturity of P.
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Plant Food and Fertilizers• The presence of potassium is essential for
several reasons:– It increases the plant’s resistance to disease.– It encourages a strong, healthy root system.– It is essential for starch formation.– It is needed for the development of chlorophyll.– It is essential for tuber development.– It encourages the efficient use of carbon
dioxide.
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Plant Food and Fertilizers
• Potassium deficiency appears as a marginal yellowing or scorch on the edges of the leaves on the lower portion of the plant.
• This is easily mistaken for moisture shortage during dry soil conditions.
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Plant Food and Fertilizers
• Lime (CaCO3)
– Lime furnishes calcium, one of the most important of the minor food elements.
– Calcium is important in the formation of plant cell walls.
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Soil Acidity (pH)• Most plant grow best in soil with pH from 5.6
to 7.0.
• 7.0 is neutral
• Values of 1-6.9 are acidic.
• Values of 7.1-14 are alkaline or basic.
• Soils tend to be acidic in areas where the parent material of the soil was acidic and where the amount of rainfall exceeds evaporation of moisture from the soil.
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Soil Acidity (pH)
• This is due to water draining through the soil and washing out the salts of sodium and calcium.
• In areas where water evaporation form the soils is equal to or greater than the amount of rainfall, the salts of calcium and sodium tend to build up in the soils and increase the pH level.
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Soil Acidity (pH)
• These salts may build up enough so much that plants cannot grow in these soils.
• This occurs in many areas west of the Mississippi River.
• Whenever it is necessary to lower pH materials such as sulfur, iron sulfate, or aluminum sulfate may be used.
• Flushing these soils with low-salt irrigation water will also lower pH.
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The Aboveground Environment• The aboveground environment may be
explained by the factors affecting plants.
• These include:– Temperature– Light– Humidity– Plant diseases– Insects– Gases or particles in the air
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Temperature
• The temperature of the air has one of the strongest effects plant growth.
• Generally the plant growth rate increases as temperature increases up to temperatures of about 90 F.
• Providing that moisture is available to the plant and wilting doesn’t occur.
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Light
• Light must be present before plants can manufacture food.
• No green plant can exist for very long without light, whether that source is sunlight or light from an artificial source.
• Light affects plants in other ways.
• Some plants bloom only when the days begin to shorten. Ex. Chrysanthemums
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Light• Plants may be classified in 3 groups according to
this flowering reaction.– Short day plants
• Chrysanthemum and Christmas cactus
– Long Day plants• Lettuce and radishes, flower when days are long and nights
are short.
– Indifferent plants• Are plants that do not depend upon certain periods of light
or darkness to flower. African violets and Tomatoes.
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Humidity
• Most plants are not affected drastically by a minor change in humidity, the moisture level in the air.
• Most plants grow best in the 40 to 80% relative humidity range.
• Relative humidity is the amount of moisture in the air as compared with the % of moisture that the air could hold at the same temperature if it were completely saturated.
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Humidity
• When the humidity is very high (80 – 100%) other problems may arise.
• One of these is high humidity may cause the spread of fungus diseases
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Plant Diseases and Insects
• Any time a plant is suffering from disease or insect damage, production is reduced.
• The amount of reduction depends on how severe the damage is and what % or part of the plant is infected.
• Stem injury may clog up a stem and kill the entire plant because the supply of water and minerals to the plant top and food to the roots is completely cut off.
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Gases and Air Particles
• Carbon Dioxide is vital to plants for the production of food.
• There is rarely a severe enough shortage of CO2 to cause damage to plants.
• Some air pollutants damage plants.
• Sulfur dioxide from coal furnaces and carbon monoxide from cars are known to reduce plants growth and in severe cases, to kill plants.