ENVIRONMENTAL REQUIREMENTS
FOR GOOD PLANT GROWTH
Unit 4
Objectives
• List 4 factors that affect the roots of plants
• Describe the differences between clay, sandy, and
loamy soils and identify a sample of each
• Explain 3 ways to improve soil drainage and 2 ways to
increase moisture retention of soil
• Explain what is meant by pH value of soil
• List 4 aboveground requirements for good plant
growth
• List the 3 major plant food elements and 2 functions
of each
The Plant Environment
• In order to grow properly, plants require a certain
environment – divided into 2 parts:
• The Underground in which the roots grow and live
• Require optimum plant food balance, temperature, water
and oxygen balance, disease and pest control
• The Aboveground in which the plant visibly exists
• Require optimum light and temperature
• Control insects and diseases
THE UNDERGROUND ENVIRONMENT
• Rhizosphere – 24 inches of soil just below the earth’s
surface
• Soil – Made of sand, silt, and clay, organic matter,
living organisms, and pore spaces with water and air
• Very important factor that affects growth and
development of all plants
• Medium (plural – media) can be soil or soil substitute
• Anchors the roots and help them take up oxygen,
moisture and minerals – all vital to plant life
CLASSIFYING SOILS
• Soils are classified according to the amount of sand,
silt and clay they contain
• Particles vary greatly in size
• Sand – largest
• Silt
• Clay – smallest
• Hold moisture and plant food effectively
• Some clay in all soil is important
SOILS – GENERAL COMPOSITION
• Soils vary greatly –
depending on origin
• Normal soil profile
consists of 3 layers
• A.)topsoil (& Organic)
• B.) subsoil
• C.) soil bedrock or
lower topsoil
SOIL COMPOSITION
• A. Topsoil – depth normally plowed or tilled
• Contains the most organic matter or decaying plant parts
• B. Subsoil – deep rooting plants send their roots to
this layer
• Well-defined layer beneath the top soil
• Well drained soil allows deep root growth
• Roots penetrate until they hit rock, hard clay, or water
• C. Soil bedrock - if rock not present then lower
topsoil
SOIL COMPOSITION
• Most soil is 50% solid and 50% air and liquid
• 45% mineral matter, 5% organic matter
• 25% each water and air (pore space)
• Ideal ratio
Is 50/50
COMPOSITION OF SOILS – PORE SPACES
• Amount of moisture and air a soil hold depends on
the soil structure and type of soil
• Sandy soil has large pore spaces and well drained
• Increase clay content
increases water held and
may become poor
draining, not allowing
enough oxygen to roots.
TYPES OF WATER IN SOIL
• Gravitational Water
• Soil is unable to hold against the force of gravity
• Becomes part of the ground water or drains away
• Of little value to plant as it drains away quickly – carries
soluble plant food with it
• Seen more in soils with large pore space
TYPES OF WATER IN SOIL
• Capillary Water – held against force of gravity in small
pore spaces and thin film around particles
• 3 Types of Capillary Water
• 1. Free – moving capillary water
• 2. Unavailable capillary water
• 3. Available capillary water – or field capacity
CAPILLARY WATER
• 1. Free moving capillary water
• Moves in all directions
• Soil saturated at low levels for water to move upward
• Actually very little upward movement of water
• 2. Unavailable capillary water
• Not available to plants
• Held tightly by soil particles and moved as vapor
• Called “air dry” – under normal drying conditions, no
more moisture will move
CAPILLARY WATER
• 3. Available capillary water or field capacity
• The water left after capillary movement stops
• Water doesn’t continue to move through the soil at this point
• Plant roots must continue to move in search of water
• Soil surrounding them is dried out by root absorption
• Roots will not grow in air-dry soil where no moisture is present
• Field capacity is high in heavy soils (clay particles)
• More surface area + smaller pore spaces for water to cling to
• **Most important water for plants!
• Plants can use about ½ this water
TYPES OF SOIL
• Sandy Soil – aka Light
• Sand and silt make up less than 20%
• Drain well, but do not hold moisture and nutrients
• Clayey Soil – aka Heavy
• Contains at least 30% clay
• Poor drainage and aeration
• Holds more moisture than is good for plants, but
hold nutrients
Types of Soil
•
Loamy Soil –
• Most desirable for
general use
• Equal parts sand, silt
and clay
• Aka sandy loam,
clayey loam, and silty
loam
Textural Triangle
Soil Improvement
• Soils for outdoor growth
can be improved through
increased drainage,
irrigation, and addition
of organic matter and
plant food (fertilizers).
Soil Improvement
• Drainage and aeration
• Improved by changing soil structure
• Add organic matter to encourage earthworms
• Tunnels and castings increase aggregation (clinging of
soil together in crumb-like particles)
• Lime and gypsum (calcium sulfate)
• Also increase aggregation by adding sand
• Use tile drains, raised beds, and/or ditches between
beds
Soil Improvement
• Moisture Retention
• Add organic matter to improve the water-holding
capacity by up to 15 times
• Also holds plant food and allows slow release of food
• EX: animal manure, green manure (plow under green
cover crop), peat moss and sawdust
• Mulch – wood chips or bark help reduce runoff, keeps
soil cool and reduces evaporation loss
• Use Fertilizers when needed and according to soil
test recommendations
(4B Notes)
Nutritional Deficiencies
• Plant food or
nutritional
deficiencies
often show up
on the leaves
Nutritional Deficiencies
• Nitrogen – deficiency
• Yellow or pale green
leaves
Phosphorous – deficiency
• Shows up as a purple
color on the underside
of the leaf
Nutritional Deficiencies
• By the time these
symptoms appear on the
leaf of the plant, the
damage has already
been done.
• Avoid this by using a soil
test to determine plant
needs
Soil Pests and Disease Control
• Soils harbor diseases such as root rot and wilt,
nematodes and insects – all can damage roots
• Control by:
• Planting resistant varieties
• Use chemicals sparingly
• Natural controls such as crop rotation
• Pasteurize soil used in containers by heating thoroughly
to 180oF for 30 minutes
Planting Media Mixes
• Most planting mixes for
use in greenhouses and
nurseries (and home
gardens) use little or no
actual soil
• AKA “soilless media”
Using Soilless Media Mixes
ADVANTAGES
DISADVANTAGES
• Mix is uniform
• Mixes are sterile (no weeds,
bugs, diseases)
• Soilless mixes lighter – easier
to handle and ship
• Good moisture retention and
drainage
• Since they are light, the
containers may blow over
• Mineral content is low –
minor plant food elements
may be missing
• Plants may hesitate to
extend roots when
transplanted into soil
Content of Mixes
• 1. Perlite – gray- white material of
volcanic origin. Improves
drainage and aeration
• 2. Sphagnum Moss – dehydrated
acid bog plants – shredded form.
Used to cover seeds – sterile and
lightweight, controls moisture
and disease
• 3. Peat Moss – partially
decomposed vegetation
preserved underwater from
marshes, bogs, swamps. High
moisture holding capacity
Content of Mixes
• 4. Vermiculite – very light,
expanded mineral ore, neutral
pH, high moisture holding
capacity
• 5. Limestone – calcium
carbonate –Ca(CO3)2 – raise pH
• 6. Tree Bark – pine or oak –
broken into small pieces (not
always!)
• 7. Slow-release fertilizers –
Plant food that is gradually
made available to plants
Content of Mixes
• Most mixes contain 2 or more of these ingredients
• Depends on requirements:
• For increased drainage and/or aeration – use mixes with
bark and/or perlite
• For moisture retention – use high organic material such as
sphagnum or peat moss
• Most popular mix: 50% sphagnum moss and 50%
vermiculite with slow release fertilizer. (sustainable/safe?)
• Other popular mixes 1/3 sphagnum, 1/3 peat, 1/3 perlite
• Can also be used as a soil conditioner/amendment
Plant Food and Fertilizers
•Plants grown in any
type of soil or soilless
mixture need
nutrients that are
readily available
•Plant food must be
water soluble
Plant Food and Fertilizers
•WATER
• Most important plant food element!
• Makes up 90% of weight of plants
• Most limiting factor in plant growth
• Only 1% absorbed by plant is used
• Other 99% lost through transpiration
Transpiration
• Transpiration of water is high
when soils are wet and the
stomata open wide to allow
more water to escape.
• For each 10 degree increase in
temperature C, the loss of
water is doubled.
• A single corn plant can lose 2
quarts of water per day.
• Stomata open in response to
light.
• Transpiration is of little value.
The cooling is minimal.
Plant Food Elements
•Major Elements
• Required in large
amounts
• nitrogen
• phosphorus
• Potassium
• (NPK)
•Minor Elements
• Required in smaller
amounts
• calcium
• magnesium
• sulfur
• iron
• manganese
• boron
• copper
• zinc
(4C and D Notes)
Nitrogen
•Generally comes in 4 forms
• 1. Nitrate of soda (NaNO3) – highly soluble,
lowers soil acidity (16% N)
• 2. Ammonium Nitrate (NH4NO3) – not as soluble,
longer time period (33%)
• 3. Ammonium Sulfate ((NH4)2SO4 – available
slowly, increases soil acidity (21%)
• 4. Urea Formaldehyde, organic form – very slowly
absorbed (38%)
Nitrogen
•Most noticeable effect on plants (of NPK)
•Encourages above ground vegetation growth
and gives a dark green color to leaves.
•Produces soft, tender growth
• ex: Lettuce – tastes good
•Seems to regulate the use of other major
elements.
Nitrogen
•Too much nitrogen may
•lower plants resistance
to disease,
•weaken the stem, due
to long, soft growth
• lower the quality of
fruit
• delay maturity or
hardness of tissue.
Nitrogen
•Not enough Nitrogen
results in plant being
•Yellow or light green
in color
•Stunted in root and
top growth
Nitrogen
• Nitrogen is easily lost from the soil by leaching
(washing) out
• Organic matter helps hold insoluble nitrogen
• Excess Nitrogen should be avoided because:
• 1. It is quickly lost from the soil through leaching,
especially in sandy soils
• 2. it can damage plants if applied in too great an amount
(fertilizer burn)
• Some plants - legumes (peas, beans, etc) put
nitrogen back into soil
Phosphorous
•4 forms:
•1. Superphosphate (20%)
•2. Treble phosphate (46%)
•3. Rock phosphate (25-35%)
•4. Ammonium phosphate (48%)
•Phosphorous held tightly by soil, not easily
leached
•Not usually available to plants, must be added
Phosphorous affects plants
•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
Phosphorous
•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
Potassium
•Common sources: potash – potassium ash
•1. Muriate of potash (60%)
•2. sulfate of potash (49%)
•3. nitrate of potash ( 44% potash) (13%
Nitrogen)
Potassium
•Rarely available in sufficient amounts to harm
plants
•Since it is a major element, it is generally
added to the soil
•Amount is determined by soil tests
Potassium
•Encourages resistance to disease
•Encourages strong, healthy roots
•Essential for starch formation
•Necessary for chlorophyll development
•Essential for tuber development
•Encourages efficient use of carbon dioxide
Potassium
Deficiency appears as
a marginal yellowing
or scorch on the edges
of leaves on lower
portion of the plant.
Mistaken for moisture
shortage
Lime
•Lime – AKA: Calcium Carbonate (CaCO 3)
•Acts as a plant food and affect soil
acidity, which affects availability of other
plant food elements
•Furnishes calcium, - most important
minor food elements
•Important in formation of plant cell walls
4D - Soil Acidity (pH)
•pH – measure of acidity or alkalinity
•pH scale from 0-14
•Neutral – pH 7
•Acidic – below 7
•Alkaline or Basic – above 7
•Most plants grow best from pH 5.6 – 7.0
pH scale
pH preference of common vegetables
pH preference of common plants
Soil pH according to location - US
•In United States, soils tend to be acidic
where parent material of soil was acid
and rainfall exceeds evaporation
•Due to water draining through the soil
and washing out (leaching) salts of
sodium and calcium
•Occurs in Eastern US and West Coast
down to central California
Soil pH according to location - US
•Soils in US tend to be alkaline (higher pH)
in areas where water evaporation from
soils is greater than the amount of rainfall
•Salts of sodium and calcium tend to build
up, which increases the pH – to the point
that some plants cannot survive
•Occurs in areas west of Mississippi
(Grasslands/Deserts)
Adjusting pH in soils:
•To lower pH (if too alkaline) – add sulfur,
iron sulfate, or aluminum sulfate.
•Can also flush with low salt irrigation water
•To raise pH – (too acidic) add lime
•Lime also affects availability of other
plant nutrients
•Adding lime helps release phosphorous
and decreases aluminum and iron
*Nutrient uptake according to pH *
ABOVEGROUND ENVIRONMENT
•Factors affecting plants:
•1. Temperature
•2. Light
•3. Humidity
•4. Plant diseases
•5. Insects
•6. Gases or particles in the air
TEMPERATURE
•Air temperature – one of the strongest
effects on plant growth
•Some plants (cabbage, kale, lettuce)
grow best in cool conditions
•Corn, beans, tomatoes prefer hot temps
•Temps too high or too low (freezing) can
stop all plant growth
•Plant growth increases up to about 90 oF
if enough water available
LIGHT
•Must be present
before plants can
make food – can be
sunlight or artificial
•Plants vary in light
requirements,
some need full sun,
part sun, dappled
sun or shade
LIGHT - PHOTOPERIODISM
•Response to different periods of day and night
in terms of growth and maturity
•Classified into 3 groups:
• 1. Short day – flower when days are short and
nights are long – (spring)
• Ex: Poinsettias, mums, some onions – bulb
formation, some strawberries
• 2. Long day – flower when days are long and
nights are short (summer)
• EX: Lettuce, radishes
LIGHT - PHOTOPERIODISM
•3. Day length indifferent – plants do not
depend on length of light or darkness
• EX: African violet, tomato, some strawberries
• Light also affects when and how plants develop
roots and store food
LIGHT - PHOTOTROPISM
Plants grow towards a light due to producing more
growth hormone on the shady side causing
elongation. Ever see sunflowers “follow” the sun?
HUMIDITY
•Moisture level of the air
•Relative Humidity – RH –
• Amount of moisture air can hold compared to % of
moisture air can hold at same temp if air is
saturated
•Most plants grow best in 40-80% RH
•Too high humidity can cause wilting or spread
fungal diseases
PLANT DISEASES AND INSECTS
• Causes reduced
production in plant
• Lowers fruit and
vegetable quality
• Depends on severity
and location
• Can be
controlled/prevented
with resistant varieties,
crop rotation or
chemicals
GASES AND AIR PARTICLES
•Carbon dioxide (CO2) is vital to plants for the
production of food
•Greenhouses improve growth rate by adding
CO2 to air, not needed for field crops
•Air pollutants cause damage – reduces plant
growth and can kill
• Sulfur dioxide (SO2) – burning coal
• Carbon monoxide (CO) - cars