Quiz #2 Flashcards
why does the earth have longer winter nights and shorter summer days?
Because of the Axial tilt of the earth.
photosynthesis is…
converting light energy to chemical energy
what are the two kinds of pigments?
Primary: Chlorophyll A
Accessory: Chlorophyll B, Caratinoids.
What is PAR?
Photosynthetically active radiation… What we can see!
What is PPFD?
The amount of light particles that hit a surface (plant leaves) in one second. We measure light in ppfd, (Photosynthetic photon flux density)
What is DLI?
Daily light integral. Total amount of PAR in a day.
Does climate change effect PAR>
Yes, climate change is changing the atmosphere so the light is struggling to get through. It does not change daylight.
What are the two types of light?
- Direct (from the sun)
- Diffuse (scattered direct light)
And plants cannot tell the different.
What are some things that happen to light ?
Reflection, Absorption, Transmittance (what’s coming through), Emissivity (ability to emit energy which it has absorbed; heat that has been radiated back out)
There can be a lot between the light and the plant… name a few
structural barriers, shade cloths, supplemental lighting. these can reduce useable light for plants 40%-50%.
What is glazing?
A material that lets light in.
1% light increase in light = ?
1% increase in plant production
at what angle is light most effective when it hits the glazing material?
90 degrees… although it rarely ever happens
What are the most common glazing materials for greenhouse production?
glass, laminated glass, diffused glass, tempered glass, rigid plastics and plastic films
Glass: glazing material
highest light transmittance, lasts the longest 30+ years, and is the most expensive.
Laminated glass; glazing material
Constructed of two layers of bonded glass with some kind of gas between the layers. When they break, it looks like a spiderweb and is often required in garden centers for this reason.
Diffused glass; glazing material
scatters light on its way in giving better light distribution, and is preferred for veggie growers because it provides a better surface area of light.
Tempered glass
is chemically or heat treated, breaks into bits.
Rigid plastics; glazing material
made of polycarbonate and acrylic, has lifespan of about 15 years. Is less expensive, and has a reduced transmittance of light over time.
Plastic films; glazing material
Made of polyethylene, has a lifespan of 4-5 years, has two layers and reduces heat loss by 40%. This is the material used for the hoophouses at the FIC.
what are some common glazing material add ons?
- Ultra violet protection
- Infrared Radiation blockers
- Anti-condensate surface treatments
what are the three types of bulbs used in supplemental lighting?
- T-5s
- HIID- High intensity Discharge.
- Light emitting diodes (LEDs): in grow room at FIC
T-5 lighting
Full spectrum fluorescent light.
HIID- High intensity discharge
Is currently the most cost effective, can get too hot and intense.
LEDs
An electrical current passes through a microchip and illuminates a diode. can cut energy usage up to 75%, is typically low maintenance and doesn’t get too hot. LEDs are the most efficient.
How do we use lights to influence plant growth?
Photoperiodism and Phototropism
Define Photoperiodism
Photoperiodism is how plants respond to daylight. It is a developmental response that synchronizes flowering, fruiting, germination and growth.
Define Phototropism
Tropisms are directional plant responses to stimuli. Positive = grow towards. Negative = grow away from.
How do plants sense light?
Plants sense light with photoreceptors that absorb photons.
What are the two types of Photoreceptors?
- Phytochrome
- Cryptochromes
Phytochrome
Red and far red light, good for germination, stem elongation and flowering.
Cryptochrome
Blue light, good for plant height, effects flowering time and morphological patterns.
Shade escape aka Shadow avoidance
Plants can tell the difference between the shade from a rock, and the shade from a plant.
The amount of continuous (?) influences flower formation in most plants
Darkness
Short day plants
Short day plants need more than 12 hours of darkness every day, they flower in the spring and fall. Plants like poinsettias and Christmas cactus are short day plants.
How do you create short days?
Using blackout cloths. This can cause a lot of heating up in the summer, so you’ll want to use them later in the day.
Long day plants
Long day plants need less than 12 hours of darkness a day. Many garden veggies are long day plants.
How do you create long days?
Supplemental lighting. for example, if the sunrise is at 7:51, and the sunset at 6:01, run the supplemental lighting until you reach 12 hours of light for that day. Night interruption is also a way to create long days.
Growing degree days (GGD)
GGD measures heat accumulation over time. Organisms have set temperature accumulation for development. We usually use a Base 50 to determine GGD
Base 50
Base 50 is a temperature used to determine Growing degree days. The threshold, or base temperature, is the temperature under which no significant crop development is expected. Also known as Maximum temperature threshold.
what is the growing degree days formula?
High temp + low temp/ 2 = average temp.
GGDx= average temp - X
X = 50 (normally)
What does temperature regulate when it comes to greenhouse growing?
Growth, water use, germination rates, flowering, ripening.
Greenhouse edge effects, what are some things around the edges of the greenhouse that can potentially alter the environment?
Heat, light, water, air flow, humidity, space, pests, people..
How does heat loss work?
Heat is lost through three different ways.
1. Conduction
2. Convection
3. Radiation
Conduction
Heat loss/transfer through touch. Floor heating systems.
Convection
Air circulation. Cold air displaces warm air and warm air rises, fans help!
Radiation
Something giving off heat.
What are some common hot water heating systems used in the greenhouse?
Finned pipe systems, floor slabbed systems, bench top systems, geothermal heating.
Geothermal heating
Geothermal energy is heat that is generated within the Earth. It is a renewable resource that can be harvested for human use.
BTU
British thermal unit = amount of energy it takes to heat one pound of water
BTUH
Number of BTUs transferred in one hour
U value
ability of a material to transfer heat
Air temperature is not the only thing to worry about, you also need to manage the temperature of the (?)
Media! plants exist in two unique environments, above and below the soil. both need to be managed
What is a photon
A light particle.
