BIO306 Exam 2 Notes

Soil

Fragments of weathered rock mixed with organics

How is soil distinguished from underlying rock?

Higher organic matter content, organisms and roots of higher plants being included, more intense weathering, and the presence of horizons

Soil structure

Physical arrangement of soil particles

Soil texture

Proportion of sand, silt, and clay within a soil; can be determined using the soil triangle

Sand (soil)

Very porous, low in organics, subject to droughts and nutrient leaching

Sandy loam (soil)

Predominantly sand but contains enough silt and clay to hold water and nutrients, warms quickly in the spring and is favored for early market fruits and vegetables

Loam (soil)

Sand, silt, and clay in equal proportions; has good drainage and aeration as well as ability to hold water and nutrients

Silt loam (soil)

More than 50% silt, holds a lot of water, can be furrow irrigated

Clay (soil)

Poorly draining, low leaching, slow to warm and dry in the spring

Heavy soil

Takes more energy to plow, such as clay

How can a heavy soil be made lighter?

Adding organic matter, such as through compost or cover crops

Peat (soil)

Soil with slightly decomposed matter

Muck (soil)

Soil with highly decomposed organic matter

What pH range is preferred by horticultural crops?

5\.5 to 8.0

Ericaceous crops

Ones that prefer more acidic soil, such as blueberries and cranberries

What plant can be used to determine the acidity or alkalinity of a soil?

Hydrangeas; they flower blue in alkaline soils and pink in acidic soils

Why is soil pH important in horticulture?

It impacts the availability of nutrients as well as beneficial microorganisms

Media (substrate)

What roots are growing in

Peat/peat moss (soilless medium)

Decaying plant material harvested from bogs that are used for moisture and nutrient holding capabilities

Bark and wood products (soilless medium)

Bark, wood chips, and sawdust; have high N, P, and K content but decompose and lead to nitrogen problems

Soilless medium

Specified organic matter, including peat moss and bark and wood products

Inorganic materials (media)

Mineral in origin, includes sand, perlite, and vermiculite

Sand (inorganic media)

Provides good aeration and drainage, easy to pasteurize

Perlite (inorganic media)

Volcanic in origin, provides good aeration and drainage but floats in water

Vermiculite (inorganic media)

Heat treated mica with high nutrient and moisture holding capacity

Pros of soilless mixtures

Can provide good aeration and drainage, lightweight, mostly sterile

Cons of soilless mixtures

Too light to hold plants when the medium is dry, poor nutrient levels, not natural for plants

Hydroponics

Growing plants where nutrients are supplied by nutrient solution that contains nutrient salts in water

Pros of hydroponics

pH and nutrients are controlled and monitored and yield is greater; weeds, diseases, and insects are fewer

Cons of hydroponics

Expensive, algae growth can occur

Substrate hydroponics

Roots are surrounded by inert or organic materials such as sand or vermiculite

Bare root hydroponics

No physical support for plants; includes aeroponic, continually aerated, floated, and nutrient film systems

Essential element

One that a plant needs for its lifecycle, forms any part of an essential molecule, and cannot be substituted

What essential elements are obtained through H2O and CO2?

C, H, and O, which are used to create glucose (plant food)

Primary macronutrient

Element required in large amounts for normal growth and development

What are the primary macronutrients?

N, P, and K

Nitrogen deficiency symptoms

Stunted growth and chloritic leaves; often impacts older leaves first (mobile)

Phosphorous deficiency symptoms

Purple leaves, stunting, poor flower, fruit, and seed development, is mobile

Potassium deficiency symptoms

Marginal burns, speckled leaves, leaf curling, and smaller leaves. Quickly leaves out of sandy soils

Secondary macronutrient

Element needed in smaller amounts, includes calcium, magnesium, and sulfur

What is a nutrient used in if deficiency causes chlorosis?

Chlorophyll development

Micronutrients

Elements needed in trace amounts, including iron, boron, molybdenum, manganese, zinc, copper, and chlorine

Mobile nutrients

Ones where deficiency impacts older leaves first, eventually moving on to younger leaves

Immobile nutrients

Ones where deficiency symptoms occur on younger leaves

True or false: All plants require the same fertilization

False

True or false: Plants require different fertilization at different stages of development

True

True or false: Nutrients can impact susceptibility to pathogens

True

Three ways to determine nutrient deficiencies

Visual inspection, tissue test, and soil test

Organic fertilizer

One that comes from living waste and may include plant residues or animal waste

Pros of organic fertilizers

Less caustic, slow release, less likely to leach out of soils

Cons of organic fertilizers

Low in nitrogen, must be composted, insoluble and rely on microbes, odor, difficult to apply and transport

Inorganic fertilizer

One that comes from minerals

Pros of inorganic fertilizers

Available quickly, easy to apply and store, wide range of formulations

Cons of inorganic fertilizers

Leach easily, can cause damage, easy to over fertilize

Complete fertilizers

Ones that include nitrogen, potassium, and phosphorous

Incomplete fertilizers

Ones that lack one of the big three macronutrients

Broadcast application

Fertilizer is spread uniformly, often before planting; causes much waste

Topdressing application

Fertilizer is applied on top of and around a plant

Fertigation application

Fertilizer is applied with normal irrigation

How are plant growth regulators used in horticulture?

To propagate, increase yields, improve post harvest storage, and improve quality

Plant hormones (phytohormones)

Ones that are chemically characterized, biosynthesized within the plant, broadly distributed within the plant kingdom, have specific biological activity at low concentrations, and are fundamental to regulating physiological phenomena

Plant growth regulator

An organic compound that is not a nutrient and that, in small amounts, promotes, inhibits, or otherwise modifies any physiological process in plants

What is the difference between plant hormones and plant growth regulators?

Plant hormones are naturally occurring and plant growth regulators may be natural or synthetic

Requirements for a substance to be called a plant hormone

Must be an endogenous substance and an organic compound, must regulate physiology in low concentrations, must be transported within a plant, and must not be a vitamin or nutrient

Growth promoting hormones

Auxins, gibberellins, cytokinins, and brassinosteroids

Wounding and stress hormones

Ethylenes, abscisic acids, and jasmonates

Role of auxin

**Cellular elongation**, phototropism, **apical dominance,** sex expression (female), and fruit growth

Role of gibberellins

Stimulate bolting, stem elongation, flowering, sex expression (male), **dormancy and seed germination**, **fruit growth**

Role of cytokinins

**Cell division and organ formation**, senescence delaying, stomatal opening, and **lateral bud break**

Role of abscisic acids (ABAs)

**Plant stress signaling** (closes stomates during water stress), dormancy, and abscission

Role of ethylenes

**Fruit ripening** and abscission

Role of brassinosteroids

**Stress and disease resistance**, shoot elongation

Role of jasmonates

Disease and stress resistance

Propagation

Reproduction of new plants from seeds or vegetative parts

Pros of sexual propagation

Not always true to type, may or may not be uniform, conditions may not be right for germination, takes time

Factors going into seed production

Location, harvesting, washing, and storage

Where does seed production often take place?

Arid regions to avoid disease

How should seeds be stored?

In a cool, dry place

What are the three stages for a new cultivar to be certified?

Foundation seed, registration, and certification

Direct planting

Occurs when a seed is planted outdoors rather than being germinated indoors first. Easy to handle, but seeds may be difficult to sow depending on size

Indirect planting

Occurs when a seed is started indoors and transplanted outside. Less time is needed before maturity is reached, but higher costs and transport and transplant stress can occur.

Hardening off

Preparing plants for stress in a new environment by reducing water, temperature, or fertilization prior to transplantation

Physical dormancy

An impervious seed coating

Scarification

Breaking the seed coat physically or with acid

Stratification

Placing seeds in a moist chilling environment (32 to 50 degrees)

Positively photoblastic

Plants which require red light for germination (sown shallow)

Negatively photoblastic

Plants in which germination is inhibited by light (sown deep)

Asexual propagation

Propagation by vegetative means

Pros of asexual propagation

Result is identical to the parent, easy and quick, avoids juvenility

Cons of asexual propagation

More expensive, viruses pose a threat, storage and handling is more difficult, lack of genetic diversity

Rootstock

Lower portion of a plant, with roots

Scion

Stem with a bud

Explants

Single cells, pieces of plant, or tissues

Micropropagation

Multiplication of plants in vitro in sterile conditions