HORT 321 Hydroponics Midterm (Purdue)

Hydroponics became a necessity during World War II due to

- Problems with soil-borne pathogens

- Presence of night soil

- Lack of local fresh food crops

- Lack of qualified farmers in the warzone

Presence of night soil (human waste used as fertilizer in the fields, huge food safety issue)

What motivated the US armed forces to start the first viable hydroponic farm on an island?

- Lack of qualified farmers

- Problems with soil-borne pathogens

- The need to feed the local community

- Lack of local fresh food crops

Lack of local fresh food crops

Soilless culture is defined as a system of growing plants without the use of soil, with or without the use of a ___________ and with the active application of irrigation, typically provided with a nutrient solution. Hydroponics refers to water culture alone, without a ___________, or a ___________ that contributes very little to the nutrition of plants.

- substrate

- container

- production system

- transplant

substrate

What was a hydroponic system was perfected at Purdue University?

- Deep water culture

- Ebb-and-flood

- Nutrient film technique

- Kratky

Ebb-and-flood

Which two research programs that have made the most significant contributions in the development of hydroponics?

- Plant nutrition

- Space agriculture

- Integrated pest management

- Tourism

plant nutrition and space agriculture

How can a hydroponic tomato grower increase fruit quality?

- By changing relative humidity to increase the accumulation of sugars

- By increasing (to a point) the accumulation of salts in the nutrient solution

- By gassing fruit clusters with auxins to increase their sugar content

- By providing end-of-production ultraviolet radiation to stress each fruit

By increasing (to a point) the accumulation of salts in the nutrient solution

True or False: Continuously growing lettuce plants under high percentages of blue light will help increase both yield (fresh mass) and quality.

False; increasing blue light will produce darker lettuce (higher quality), but will not increase yield.

What is the main factor determining success of hydroponics for commercial production?

- The development of new technologies that can support labor shortages.

- The development of systems that can be cost-competitive with open field agriculture.

- The improvement of produce quality compared with field agriculture.

- The development of new cultivars that have been bred specifically for hydroponic production in controlled environments.

The development of systems that can be cost-competitive with open field agriculture.

Breeding for _______________ is an important priority for fruiting crops like tomato in CEA.

- Increased anthocyanin content

- Fertilizer-use efficiency

- Increased harvest index

- Disease resistance

increased harvest index

Which of the following fruit crops can be leaned-and-lowered in commercial production?

- Tomato and cucumbers

- Strawberries and hops

- Lettuce and basil

- Peppers and cannabis

Tomato and cucumbers

What is the most limiting factor for commercial hydroponic hop production?

- Harvest time

- Photoperiod requirements

- Long production cycle

- Temperature requirements

Harvest time

____________________ tomato cultivars are most commonly used commercially, as they continue to produce fruit for up to a year.

- Determinate

- Heirloom

- Indeterminate

- Bush-type

Indeterminate

_______________ propagation is more common in commercial hydroponics than starting plants from_______________, which is common for perennial herbs.

- Seed, cuttings

- Cutting, seeds

- Cutting, grafted plants

- Grafting, seed

Seed, cuttings

True or False: Stabilized plugs are commonly used for cuttings, whereas loose substrates are preferred for seedling propagation.

False

True or False: Expanded clay is more commonly used by commercial hydroponic growers in Indiana than in Florida.

False

True or False: Substrates with low cation exchange capacity are typically preferred for hydroponic production, as they enable growers to have maximum control of the nutrition of plants.

True

Open bags are more likely to be used for the production of_____________________.

- Lettuce

- Basil

- Strawberries

- Raspberries

Raspberries

True or False: Both coconut coir and rockwool are widely use in vegetable hydroponic production because of their adequate physical properties and ease of disposal.

False, rockwool is not easily disposed.

The most common hydroponic system for fruiting vegetable production is___________________

- Slab culture

- DWC

- Vertical plant towers

- NFT

Slab culture

What two factors are more likely to be affected by channel length in NFT systems.

- Solution temperature and nutrient concentration in the solution

- Solution temperature and risk of Pythium spread

- Nutrient concentration and root blockage within the channel

- Risk of Pythium spread and root blockage within the channel

Solution temperature and nutrient concentration in the solution

Which of the following would be most important for commercial hydroponic production, regardless of location?

- Net pots

- Aerators (or other oxygenation mechanism)

- Water chillers

- Buried reservoirs

Aerators (or other oxygenation mechanism)

True or False: Water chillers should not be used to manage temperature fluctuations in the solution reservoir of hydroponic systems.

False

True or False: In order to increase productivity, growers should increase the length of NFT channels to the maximum available space in their growing space.

False

______________ systems convert into DWC systems as roots develop and grow into the solution.

- Bato bucket

- Ebb and flood

- NFT

- Fogponic

Fogponic

What are two strategies discussed in class that can help tomato growers produce sweeter tomatoes?

- Providing heat close to the fruit clusters

- Increasing EC in the nutrient solution

- Reducing frequency of irrigation events

- Providing high-energy light (e.g., blue) to stress plants

Increasing EC in the nutrient solution and Reducing frequency of irrigation events

True or False: Positive DIF can help lettuce growers produce larger plants, and ornamental growers produce more compact plants.

False, a positive DIF promotes taller growth

Briefly explain the different strategies needed to control tipburn in lettuce and strawberry.

To control tipburn in lettuce, vertical fans can be used. This helps because tipburn is a calcium deficiency that is unrelated to the amount of calcium given to plants, but rather a blockage of transpiration because humidity has built up next to the surface of the leaves, and the calcium cannot be effectively distributed around the plant. The vertical fans help break up this boundary layer so that the plant can properly transpire. In vertical farms they can install mini jet tubes to combat this issue.

In strawberries, humidity needs to be increased at night to ensure that calcium is taken up to the growing point of plants. Growers can use misters or foggers to increase humidity without getting the plant wet.

__________________ and __________________ are indications that the tomato plants in our greenhouse are too vegetative.

- Suckers in flower clusters

- Thin stems

- Curled leaves

- Dark, yellow flowers

Suckers in flower clusters and Curled leaves

True or False: The optimal temperature of a crop will tend to decrease under higher carbon dioxide concentrations.

False, optimal temperature will increase under higher carbon dioxide concentrations

Light drives ________

Biomass production (growth)

Temperature drives _______

development (organ formation)

Relative Humidity (RH) affects __________

transpiration rates (ideal RH is 50%-70%)

PAR (Photosynthetically Active Radiation) Range

400-700 nm

Which kind of system is more forgiving, substrate based or non-substrate based?

Substrate based, as it can hold on to water and nutrients in the event of a power outage where the water stops being supplied to plants.

What should the DO (dissolved oxygen) levels be in the nutrient solution?

>5 mg/L or 5ppm

What is the ideal nutrient solution temperature?

68°-72° F

When should you fully replace your nutrient solution?

Every 2-3 weeks

Excess potassium inhibits __________ uptake which can lead to _____________.

Inhibits calcium uptake which can lead to blossom end rot.

To promote the vegetative state, increase _________

Nitrogen

To promote the reproductive state, decrease ___________ and increase ___________ and ___________.

Decrease nitrogen and increase calcium and potassium (stronger cell walls and increased water uptake)

What is the ideal tomato

DLI

CO₂ ppm

Day and night temperature & positive or negative DIF

Photoperiod

% humidity

DLI: 20-30 mol/m²/day (2× lettuce).

CO₂: ~1000 ppm.

Temp: 75-80°F day / 65°F night (positive DIF).

Photoperiod: 16-18 hr light / 6-8 hr dark.

Humidity: 50-70%.

List one attribute of growing peppers

- They prefer cooler temperatures and a higher EC than lettuce

- They can develop sun scald in excessive direct light

- They should grow 4-5 heads per plant and cannot be leaned/lowered

List one attribute of growing cucumbers

- They need to be harvested every other day

- Tendrils need to be removed regularly

- They are grown in blocks and seeded in house

List one attribute of growing eggplants

- There is a limited US market for them

- You must harvest the fruit immediately otherwise it will spoil on the plant

- They require minimal supplemental lighting

List one attribute of growing raspberries and blueberries

- They are grown in containers or bags in shade houses/high tunnels

- Simpler, lower cost systems

- They are gaining research attention

List one attribute of growing strawberries

- They require slightly lower DLI and EC than other fruiting crops

- They are prone to tipburn/calyx burn from a lack of transpiration (to combat this raise night humidity to increase guttation [dew on leaf edges] and Ca movement)

- They have high pest pressure (aphids)

- They need to be harvest 1-2x daily

- Grown in shoulder height gutters for easier harvest

What are common types of lettuce grown in hydroponic systems?

Butterhead and loose leaf (iceberg is grown only in field production)

What kinds of systems are popular for hydroponic lettuce?

DWC and NFT

What is the ideal DLI for hydroponic lettuce?

≥12 mol/m²/day

What is the ideal day and night temperature for hydroponic lettuce?

68-75°F day / 60-66°F night

What is the ideal RH for hydroponic lettuce?

50%-70%

What is the ideal temperature, system, and DLI for culinary herbs?

72°-75°, DWC or NFT, and ≥12-15 mol/m²/day

How are perennial and annual culinary herbs propagated and give examples of each.

Perennial: cuttings (rosemary, thyme, mint, and oregano)

Annual: seeds (basil, parsley, cilantro, and dill)

What is a positive and negative DIF and what do they promote

Positive DIF: when day temperatures are higher than night temperatures (stem elongation, taller, stretched plants)

Negative DIF: when day temperatures are cooler than night temperatures (suppresses stem elongation, smaller, compact plants)

How many greenhouse tomatoes did Indiana produce in 2014?

in the 500k-1M range

What is the difference between horticulture and agronomy?

Horticulture produces high value crops in less space. Agronomy produces low value crops in more space.

How do the root systems differ in conventional agriculture versus hydroponics?

Conventional: large root systems because they have to search for water and nutrients

Hydroponics: smaller root systems because water adn nutrients are readily available

What are some early examples of hydroponics?

The Gardens of Babylon, Egypt (early aquaponics depicted in hieroglyphics), and Greenhouses in Rome and Greece

Which two relatively recent inventions have created an industry boom in hydroponics?

Plastic and LED lights

Who is the father of modern hydroponics?

William Gericke

List some advantages of hydroponics

- Efficient water and nutrient use (water can be recycled, can be specific with which nutrients are added to reduce waste)

- Less labor needed

- Ease of cleaning

- Lack of soil borne problems

- Final product can be higher quality

- Year round production and employment

- Can be grown anywhere

List some reasons that hydroponic crops can be higher quality

- EC can be raised easily

- Can provide inter-canopy lighting

- Can provide light of specific colors (blue light is high energy which causes stress and increases anthocyanin content)

- Crops can be harvested later in ripening (more time to ripen produces higher quality fruit)

- Year round production

- Can be grown anywhere

List some disadvantages of hydroponics

- Higher capital investment ($600k-1M per acre on top of land cost)

- Higher energy use and cost

- Plant diseases and pests are hard to control

- Daily checks are needed as the plants respond to changes very quickly

- Mostly limited to high value crops that are bred for hydroponic production

List some different applications of hydroponics

- Commercial horticulture production

- Research

- Urban agriculture

- Tourist attractions

- Military

List some inorganic substrates

- LECA

- lightweight expanded clay aggregate

- ranges in size

- low WHC, free drainage

- expensive

- reusable, sterile, sustainable

- Rockwool

- heated rock spun into fiber

- sterile, lightweight when dry, high WHC, no CEC

- very basic (high pH)

- needs to be dunked in an acidic solution before use

- ideal for germination

- prone to algae, disposal issues, dust is a problem

- Perlite

- free draining

- lightweight

- sterile, no CEC, neutral pH

- can be broken to small pieces but not broken down

- dust is problem, prone to algae, can clog systems

List some organic substrates

- Peat moss

- coconut coir

- broken down coconut husk, sustainable

- neutral pH, high WHC, high CEC, easy transporting

- slow to break down, needs to be leached

Is a high or low CEC preferred?

A low CEC because this allows the nutrients to be immediately available

What is the difference between an open and closed system?

In an open system the water flows out of the system. In a closed system the water is captured and reused.

What kinds of plants are grown in ebb + flood systems?

Leafy greens, herbs, strawberries, cannabis, and vegetative propagations

What kind of plants are grown in vertical plant towers?

Leafy greens, herbs, strawberries, and culinary flowers

What is the most common system used for commerical leafy greens?

DWC

Commercial NFT systems should not exceed ________ feet in length.

12 feet