Horticulture test 3

leaf area
smaller leaf area decreases transpiration
leaf orientation
vertically oriented leaves decrease transpiration
leaf surface
waxy, hairy or shiny leaf surfaces decrease transpiration
when stomata are closed, transpiration decreases
high humidity decreases transpiration
a) low temp. decreases transpiration
b) high temp. increases transpiration, but when it gets too hot the stomata close, then transpiration may decrease
a)darkness decreases, b/c stomata close (except for CAM plants open at night)
b) high light intensity increases temp. which increases transpiration, until stomata close then transpiration may decrease; occurs midday during heat of summer.
as wind increases transpiration increases, but if it gets too windy, stomata may close and transpiration may decrease.
a) when soil is moist, transpiration occurs according to the above factors
b) when soil is too dry, stomata close causing transpiration to decrease (overrides above factors)
DECREASE TRANSPIRATION: mist or spray foilage
a) in propagation an intermittent mist system is used
b) mid-afternoon sprinkler irrigate plants in greenhouses/nurseries
DECREASE TRANSPIRATION: decrease light intensity
grow plants under shade
DECREASE TRANSPIRATION: harden off seedlings
a) decrease watering
b) decrease temperature
c) decrease fertilizer, especially N.
chemicals that close or clog stomata
a) physiologically cause stomatal closure
b) wax, resin or latex that clogs stomata
the outer weathered layer of the earth's crust
growing medium
the substrate in which plants grow. Usually appied to manufactured or synthetic soils.. EX: "potting soild", or highly amended soils (landscape beds)
Functions of soil or growing medium
1. Support and anchorage
2. Supplies mineral nutrients
3. Supplies water
4. Allows gas exchange- especially O2 and CO2, but also ethylene
Soil profile
morphology of horizons (layers) in a soil
A Horizon or topsoil
-highly weathered
-abundant life, therefore, high in organic matter
-dark coloed
plow plan
a compacted, impermeable layer in the A horizon due to repeated plowing or tilling (approx. 6 inches deep)
B Horizon or subsoil
-less weathered; higher in clay
- less life, therefore, low in organic matter
-lighter colored
clay pan
impermeable layer high in clay
hard pan
impermeable layer high in iron
C Horizon or parent material
-little weathered
-little life, except deep rooted plants and little to no organic matter
D Horizon or bedrock
- rock base
uptake of water by roots
movement of water through plants, mainly through xylem
-loss of liquid water from leaves
- occurs through hydathodes (similar to stomata, but they do not close)
young roots
most absorption, manly through roots hairs
YOUNG ROOTS: very numerous
14 billion on a typical rye plant
YOUNG ROOTS: large surface area
14,000 ft2 (1310 m2) on a typical rye plant
YOUNG ROOTS: rapidly and constantly produced
975 linear ft (300 m) er day on a squash plant
older roots
little absorption due to:
a) suberization of endodermis
b) periderm (bark) formation
Cohesion Theory of Translocation in the Xylem
1) Transpiration occurs and is driving force
2) Causes negative pressure in leaves
3) Column of water is pulled up in the xylem and translocated
driving force for translocation
transpiration causes a negative pressure in leaves, which "pulls" the water up the xylem
evaporative coling of leaves
540 cal of heat energy is dissipated for every gram of water that evaporates from leaves, which is a major contributor to the cooling of leaves
Organic Soil
contain 20% or more organic matter
peat soil
contains greater than 65% organic matter (Sphagnum is the BEST)
muck soil
contains 20-65% organic matter
Mineral Soil (field soil)
contains less than 20% organic matter
4 Major Components (in a well watered, but well drained loam soild)
air, water, mineral particles, organic matter
approx. 25% of volume; in larger pores
approx. 5% of volume; in smaller pores
Mineral Particles
44-49% of volume
Organic Matter
typically about 1% in nature
partially decayed organic matter on the soil surface
highly decomposed, fine, amorphous organic matter in the soil
SAND: Physical
structurally simple; relatively unweathered, physically broken down parent material
SAND: Chemical
relatively inert; results in:
a) a little effect on soil chemistry and pH
b) poor nutrient holding capacity (CEC)
Pore Space
a) less total pore space
b) more large (macro) pores, fewer small (capillary) pores
Sand causes...
1) increased aeration
2) increased drainage
3) decreased water capacity
intermediate chemical and physical properties between clay and sand
CLAY: Physical
structually complex
a) colloidal
b)wet: viscous and gelantinous; sticky--dry: hard, packed and cohesive
c) Micelles: laminated into stacks
d) very large surface area
e) very small pores
CLAY: Chemical
very complex; negatively charged.... more
negative log of the hydrogen ion concentration
Low pH (below pH 5.5)
Cu,Zn, had B,Fe with a Mn
Intermediate pH (pH 6-7)
High pH 9above pH 6.5)
Mo, N, K Ca,S,Mg
Chemicals that increase pH
lime, dolomite, nitrate
Chemicals that decrease pH
sulfur, sulfate, acidic fertilizers (urea, ammonia, ammonium)
Acid soils
soils with acid pH; in areas of high rainfall
Basic or Alkaline soils
soils with basic pH; in arid regions
BASIC: saline soil
pH 7-7.5 and greater than 2,000 ppm total soluble salts
BASIC: sodic soil
pH 8.5-10, 15% or more of CEC is occupied by Na.
BASIC: saline-sodic soil
pH 8-8.5, greater than 2,000 ppm total soluble salts and 15% or more of CEC occupied by Na
3 ways to improve saline, sodic, or saline-sodic soils
leach-- application of large volumes of water to remove excess soluble salts
Add element sulfur (S)-- acidifies the soil
Add gypsum-- Ca promotes good soil structure, drainage and Na leaching