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- chemical, made within the plant, that produce changes in growth
- cause root formation, seedless fruit formation, leaf drop, and stem lengthening
Plant growth regulators
synthesized chemicals like plant hormones, which have the same effects.
- the first hormones discovered have such diverse effects:
- promotion of rooting
- formation of underground tubers and bulbs
- Prevention of fruit formation, defoliation
- Prevention of abscission of leaves and fruits
- Promote Juvenility
- Auxin manufactured in the terminal bed is also responsible for suppressing the sprouting of axillary buds further down the stem of a plant
- is a retardant
- Later determined to be ethylene gas given off in the fumes that caused accelerated ripening
- Also produced by the ripening fits themselves, wounded plant parts or by cut flowers
- Ages plant parts
- are used occasionally as stimulants for plant growth and for use after transplanting
- Never be used in place of fertilizers
- Temperate: seasons, warm summer/cold winter, most of U.S.
- Subtropical: warm summer, mild winter, west coast, S.E. US, mediterranean climate
- Tropical: Warm year round, only "season" may be wet/dry, Hawaii
- Monsoon: Seasonal rain, no monsoon climate in US but sometimes have monsoon seasons
- Mediterranean climate
- mild wet winter
- dry summer
- two growing seasons
- Moist soils and longer days
- spring as days lengthen
- fall after the first rains
- For majority of plants in temperate zones, spring is when the majority of yearly growth takes place
- yearly growth flush includes:
- -Leafing out of trees
- -Emerging and blooming of bulbs
- -Blooming and fruit setting in fruit trees
- -New shoot growth in shrubs and trees
- Summer is a period of maturing in plants
- some plants have their flowering period (Tomatoes and corn)
- others, which flower in the spring enlarge/ripen fruits (deciduous fruit trees, apples)
- New, tender spring leaves toughen
- Many plants accumulate energy in the summer to enable them to live through the winter
- In temperate climates Fall is a transitional season for plants that live many years and the end of life for those living one season
- These surviving the winter enter dormancy to ensure their winter survival:
- -triggered by short days, cooler weather, or both
- -stop growth, drop leaves, decrease water content in the sap
- Plants that live one year must have produced seed capable of sprouting in spring
- Time of waiting
- -when temperatures are below freezing, water is solid and cannot travel readily throughout the roots and stems.
- Lack of water and leaves drastically slows biochemical processes in the plant
Elements combining to make up a climate:
the geographic range over which a plant will grow
- the lowest temp a plant can stand
- for many plant 28 degrees F is the minimum because at this temp the liquid contents of the plant cells freeze and expand, killing the plant
- In many plants the woody stem or root system is frost-hardy but not the flowers and leaves
- occurs when the air is cool and calm and skies are clear
- warmth from the sun accumulated by the soil and plants during the day is lost at night as heat radiating upward
- Radiation frost
- second type of frost is caused by a cold airy mass moving into an area, this is usually a more severe frost
- sprinkler irrigation of plants is used to prevent frost
- Rain, snow, hail, and sleet
- lack of rainfall is limiting factor to plant growth
- water stress can be a major growth limiting factor
- Coastal fog can supplement lack of rainfall
- Excessive rain or rain occurring out of season can be as detrimental to plants
- Frequent rains spread plant diseases by splashing microorganisms from one leaf to the next
- Snow cover plan an important role in plant survival in areas with cold winters
Precipitation- Snow cover
- Snow cover plays an important role in plant survival in areas with cold winters
- insulates low-growing plants form cold air
- protects stems form freeze drying
Percipitation-sleet and hail
- tear leaves and bruise or knock off fruits
- Freezing rain can often cause branch breakage on trees
- occurs when the air is warm and humid
- after sunset, the air temperature drops, and the atmosphere is unable to contain the amount of water it held during the daytime. The water then precipitates out over the area in small droplets called dew
- can be a factor in the spread of diseases in turf grass
What can high auxin concentrations be used for?
What are they used for in commercial agriculture?
- To prevent fruit on ornamental trees when the fruit is undesirable feature.
- In commercial ag synthetic auxins are used to defoliate plants before harvest, prevent sprouting of potatoes in storage, and prevent premature fruit drop in orchards.
- a second group of hormones
- associated with stem elongation
- other effects: breaking dormancy of seeds, buds, and tubers and inducing flowering in plant that normally require vernalization or a specific photoperiod.
- Used in greenhouses to form tall treee-form fuchsias and geraniums form cuttings because of their stem-elongation ability.
Plants that are able to to survive temperature lower than freezing are called frost-hardy
some houseplants and many tropical plants suffer from chilling injury at temperatures less than fifty degrees F. this is why bananas turn black in the fridge.
For temperate-zone fruits such as apples and cherries, an adequate number of cold days per winter, called the plant's chilling requirement
Growing degree requirement
- each crop also needs a certain number of adequately warm days in order to mature
- A baseline temperature is subtracted from the average temperature for a given day
Hoar frosts vs black frosts
- Hoar Frosts: crystal depositing frosts
- they occur when moisture from humid air condenses onto the plants because of the drop in temperature
- Black Frosts: if the moisture content of the air is low, the air temperature can reach freezing without moisture condensation, but plants will still be injured
the freezing of the soil causes the water contained in it to expand, this may cause a condition called frost heaving, in which the soil pushes up in chunks from around the roots of plants leaving deep cracks over the root area.
decrease in temperature of a wet object when water evaporates form its surface
- may determine how well a plant will grow
- defined as the amount of water the air contains relative to the amount it is capable of holding at that specific temperature
- the higher the temp, the greater the amount of water the air can hold
- Duration, intensity, and quality affect growth of outdoor and indoor plants and may control flowering.
- duration depends on distance from the equator
Areas in the home can be categorized into three categories:
- 1. full shade: where the sun rarely shines directly
- 2. Partial shade/partial sun: sunlight about 1/3 to 1/2 of the time
- 3. Full sun: on the south sides of houses or where there are no trees shrubs, or structures that block the light
- Ocean wind limits number of plants that can be grown near the shoreline
- Desert winds increase the rate of moisture loss from the soil and plant leaves
- subzero winds damage evergreens by removing moisture from the foliage, essentially freeze-drying it
Natural factors modifying climate include:
- distance from the equator
- nearby presence of large bodies of water
the higher the elevation of an area, the colder the average year round temperature
sloping terrains also can vary several degrees in temperature from the top portion of the slope to the lower part or valley. Cool air, which is heavier than warm air, will flow down a slope and collect at the bottom, a phenomenon called air drainage.
Bodies of water
larger bodies of water absorbs heat in the summer, making adjacent land cooler and gives it off in the winter raising the temperature
- air pollution can be composed of both gases and small airborne pieces of matter; combining and becoming smog
- smog affects plant growth by temperature modification. acts like an insulation layer over an area and prevents heat from escaping to the atmosphere. decreases the intensity of light, giving plants less light form which to manufacture carbohydrate.
- Main way smog affects plant growth is through foliage injury by toxic gases.
- small areas that have slightly different climate characteristics than the surrounding land. many be less windy, shadier, moister, warmer, or in any other way different form the typical climate.
- Outdoor Microclimate: example is a frost pocket, or under a tree where it is shadier and cooler
- Indoor Microclimate: Upstairs compared to a downstairs in a house. north side compared to the south side of a house
Plant adaptive strategies
- desert plants store water in their leaves and can protect themselves from excessive sun exposure.
- at high elevations both cold temperature and drying winds become factors in plant survival.
the elevation at which trees can no longer grow because of climate extremes. But other plants do grow
USDA plant hardiness zones
- maps showing zones of minimum winter temperatures in the U.S. and Canada
- Eleven zones are outlined, ranging form completely frost-free areas in Florida, Texas, and California to negative fifty degrees in Canada.
American Horticultural Society Heat-zone map
- The USDA plant heat zone map addresses plant hardiness in excessively hot temperatures instead of excessively cold temps.
- by the average number of days per year that the areas experience temps over 86 degrees F.
How are mineral soils classified?
- by the size and quantity of mineral particles present in the soil.
- From clay to silt to sand
- including muck and peat
- contain predominately decaying organic matter with smaller amounts of mineral components.
- Generally found in small pockets in the north central and northeastern sections of the United States and Canada as well as in the Everglades region of Florida.
- very fertile, but do not respond in many respects in the same manner as mineral soils.
- often referred to as heavy soils composed primarily of platelike clay particles.
- small spaces between clay particles (pore spaces) account for one of the main properties of clay soils- slow water and air movement into and out of the soil
property of clay soils attributable to the flattened shape of the particles is plasticity. This the property of clay responsible for its being sticky and moldable when wet and hard and cloddy when dry.
- or light soils
- do not retain moisture well; nor do they expand and contract, or compact readily
- CEC is low
- large particle size
- possess qualities of both sand and clay proportional to the relative amount of clay or sand in the loam soil
- ideal for most plants
- will absorb a large quantity of water and not require frequent irrigation, yet dry enough to be workable in a shorter amount of time than a clay soil
- hold more nutrients than do sandy soils
Soil texture triangle
a graphic representation of the percentage combinations of the three basic types of soils in natural soil and the the type of solid formed by each combination
Organic Matter in the soil
- is the result of vegetative matter such as leaves and roots and animal products such as manure returning tot he soil and decomposing.
- In sandy soils, organic matter increases water and nutrient-holding capacity
- in clay soils it improves drainage and air movement
- clay particles have a tendency to lie very close together and exclude air
- the clumping together of soil particles into large groups
when organic matter decomposes, the resulting humid acid acts as a glue and casuist the clay particles to clump together loosely.
- is the relative capacity of the soil to attract and hold nutrients (cations) on the surface of the soil particles.
- the ability of a growing medium or soil to attract and hold nutrients
Soils with poor CEC
the numbers of cations each sand particle can attract is quite low
Soils with high CEC
such as clays or those high in organic matter, a very large quantity of nutrients can be held by each soil particle
Fertilizers and CEC
- fertilizers need to be applied less frequently to soils high in CEC because of the nutrient storage capabilities.
- fertilization can be reduced in high CEC soils by using fertilizers with nitrogen or urea
Cohestion vs Adhesion
- Cohesion: the attraction of identical molecules for each other, for example the cohesion of water molecules
- Adhesion: the attraction of liquids for solids, for example, the attraction of water for soil
Permanents wilting point
the only water left in the soil is hygroscopic water, which is held too tightly by the soil particles for plants to remove. Thus, available water plant growth is that water between field capacity and the permanent wilting point.
- the layers in soil. They can be distinguished by the change in color between the layers.
- the topmost horizon is called the A horizon which corresponds with the topsoil
- B and C horizons are the subsoils with are low in organic matter and relatively infertile
- hardpan- a layer of compacted soil that slows or stops the movement of water and air and the growth of roots into lower layers. can occur naturally or the result of heavy equipment moving over the soil.
- the movement of soil par tiles from one place to another and is a process that is detrimental to the fertility of the soil.
- water and wind are usually the agents of the movement with the soil either being washed by heavy rain or improper irrigation or blown away by the wind
Large + animals include mammals like gophers and mice, plus burrowing insects such as crickets, beetles that tunnel and brings subsoil to the surface on a continual basis
pH of a soil
- is a measure of its acidity or alkalinity
- measured on a logarithmic scale that runs from 0 to 14.
- 7 is neutral
- optimum range for the majority of plants is 6.5 to 7
What is used to raise the pH of soil
What is used to lower the pH of soil
- sulfur or aluminum sulfate
- or by using organic amendments such as oak leaves, pine needles, or sphagnum moss that are acid-forming
- resistant to pH change
- soils with a high buffering capacity will require larger quantities of pH-adjusting materials than those with a low buffering capacity.
a material added to soil to improve physical properties such as drainage, CEC, aeration, and water retention.
- is composed of partially decomposed plants and is made from rotted garden refuse such as weeds, grass clippings, fallen leaves, and plant clippings.
- material should be kept damp by sprinkling with water as necessary
- are known to be used by plants are classified for was of discussion into two groups:
- used in fairly large quantities by plants:
- -Nitrogen (N)
- -Phosphorus (P)
- -Potassium (K)
- -Calcium (Ca)
- -Magnesium (Mg)
- -Sulfur (S)
- -Hydrogen (H)
- -Oxygen (O)
- -Carbon (C)
- trace elements, used in small quantities include:
- -Iron (Fe)
- -Copper (Cu)
- -Zinc (Z)
- -Boron (B)
- -Molybdenum (Mo)
- -Manganese (Mn)
- -Cobalt (Co)
What happens when nitrogen is lacking?
What does it stimulate?
- plants grow slowly and loose their deep green color, especially on lower leaves.
- stimulates rapid vegetative growth, disadvantage of stimulating leafy growth
What does phosphorus influence?
- flowering and fruiting, root development, disease resistance, and maturation
- because it is insoluble, it will remain where it is placed and will not leach through the soil
What is potassium essential for?
essential for starch formation, movement of sugars, formation of chlorophyll, and flower and fruit coloring
- derived from decomposition of plant and animal products
- include blood and bone meal, manure and sewage sludge
- manufactured using raw materials such as natural gas and phosphate rock
- more concentrated than organic fertilizers
- can be fast or slow release
- the series of transformation nitrogen undergoes in the environment
- Nitrogen comprises about 70% of the atmosphere
Legumes with the aid of bacteria that live in nodules on their roots, are able to enrich the soil by fixing atmospheric nitrogen found in the air spaces in the soil
- soluble powders
Most common form of fertilizer
- slow release because nutrients need not soluble in water
3 categories based on numbers of NPK on fertilizer bag
- Balanced fertilizers: all the same 8-8-8
- Complete fertilizers: contain some of each 5-10-15
- Single element: one of the three 46-0-0