Soils and Media

Objectives

• Know about true soil texture

• Know how organic material relates to horticulture and soils

• Know why pH is important to plants

• Know the four types of media, characteristics of them, and pros and cons of each

What is soil?

Soil..Fragments of weathered rock mixed with organics

Soil contains pores with air and water

Soils is distinguished from underlying rock in four ways:

1. Higher organic matter content

2. Organisms and roots of higher plants being included

3. More intense weathering

4. Horizons being present

Soil develops from parent material, air, water, and organic material

Soil composition is determined by climate, organisms, relief, parent material, and time (ClORPT)

Soil Texture and Structure

Soil texture..proportion of sand, silt, and clay within a soil

Names of soil textures can be determined by using the soil triangle

Soil structure..physical arrangement of soil particles

A soil’s structure impacts pore size, water holding capacity, and air penetration. Soil compaction, tillage, traffic, and rainfall can impact soil structure.

Clay is the smallest particle in soil and sand is the largest.

Soil Classes

Sand..very porous, low in organics, and subject to droughts and nutrient leaching.

Sandy loam..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..sand, silt, and clay in equal proportions; has good drainage and aeration as well as ability to hold water and nutrients.

Silt loam..more than 50% silt, holds a lot of water, and can be furrow irrigated.

Clay..poorly draining, low leaching, slow to warm and dry in the spring.

Heavy soils, such as clay, take more energy to plow than light soils, like sand.

To lighten soil, organic matter can be added, for example through compost and cover crops.

Peat..soil with slightly decomposed organic matter

Muck..soil with highly decomposed organic matter

Soil pH

Most horticultural crops like a pH of 5.5 to 8.0

Ericaceous crops (blueberries, cranberries) prefer more acidic soil (5.0 to 5.5)

Hydrangea flowers blue in alkaline soils and pink in acidic soils

Soil pH impacts the availability of nutrients as well as beneficial microorganisms

pH can be adjusted to avoid plant diseases

Lime can be applied to lower soil acidity, though it takes time.

Sulfur compounds can be applied to lower soil alkalinity and work very quickly.

Natural pesticides, such as copper applied to the leaves of citrus plants, can affect soil pH.

Media

Media..also known as substrate, describes what roots are growing in

Good media provides anchorage, aeration, drainage, nutrient holding capacity, and water holding capacity.

True soil is becoming rare, and is being replaced with soilless medium.

Peat/peat moss..decaying plant material harvested from bogs, used for moisture and nutrient holding capacity

Bark and wood products..bark, wood chips, and saw dust have N, P, and K, but decompose and lead to N problems

Soilless medium..specified organic matter, includes peat moss and bark and wood products

Inorganic materials..mineral in origin, includes sand, perlite, and vermiculite

Sand provides good aeration and drainage and is easy to pasteurize

Perlite is volcanic in origin, provides good aeration and drainage, but floats in water

Vermiculite is heat treated mica with high nutrient and moisture holding capacity

Soilless mixtures can provide good aeration and drainage, are lightweight, and mostly sterile, but are too light to hold plants when the medium is dry, has poor nutrient levels, and are not natural for plants

Hydroponics

Hydroponics..growing plants where nutrients are supplied by nutrient solution that contains nutrient salts in water.

Hydroponics are often used in northern greenhouses in the winter for very high value crops

In hydroponics pH and nutrients are completely controlled and monitored, yield is greater, and weeds, diseases, and insects are less, but it can be expensive and algae growth causes issues.

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

Containers

Containers should always have drainage holes. Pots and flats with chromated copper arsenate or pressure treated wood should be avoided. Wood preservatives should be avoided as they are phytotoxic. Clay pots dry more quickly and accumulate salts on the outside. Plastic pots are less breakable and lightweight, but warp when disinfested and take hundreds of years to break down.

Nutrients

Objectives

Know what constitutes an essential element

Know macronutrients vs. micronutrients

Know some symptoms of nutrient deficiency

Explain the difference between organic and inorganic fertilizers

What is an essential element?

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

There are 16 essential elements, 3 of which are obtained through H2O and CO2 (C, H, and O).

Plant “food” is made from carbon dioxide and water. Irrigation provides a steady supply of H and O, and carbon dioxide is typically sufficient at 350 ppm but can be raised to 1500 ppm to improve greenhouse production.

Primary Macronutrients

Primary macronutrient..element required in large amounts for normal growth and development.

Primary macronutrients are nitrogen, phosphorous, and potassium

Soils are typically deficient in at least one macronutrient

Nitrogen

Nitrogen is used to make chlorophyll, amino acids, proteins, and nucleic acids.

Nitrogen deficiency symptoms..stunted growth and chlorotic leaves; often impacts older leaves first.

Nitrogen is soluble and often leaches from the soil. Nitrogen sources are mostly organic material.

Phosphorous

Phosphorous is used to create proteins, nucleic acids, and ATP

Phosphorous deficiency symptoms..purple leaves, stunting, poor flower, fruit, and seed development; moves from older to younger tissues (mobile).

Potassium

Potassium is used in enzymatic reactions, protein synthesis, meristematic growth, and guard cells.

Potassium deficiency symptoms..marginal burns, speckled leaves, leaf curling, and smaller leaves.

Potassium quickly leaches out of sandy soils

Secondary Macronutrients

Secondary macronutrient..a macronutrient needed in smaller amounts

Calcium

Calcium is necessary for cell division, cell growth, and cell wall formation.

Calcium deficiency symptoms..malformed buds, poor root growth, and coping of leaves

Calcium deficiency is known to cause blossom end rotting in tomatoes

Magnesium

Magnesium is used for chlorophyll as an enzyme activator

Magnesium deficiency symptoms..interveinal chlorosis of older leaves

Sulfur

Sulfur is important in plant vitamins and amino acids

Nitrogen deficiency symptoms..chlorotic foliage on new leaves

Micronutrients

Micronutrients are needed in trace amounts

Iron

Iron is important in enzymes, chlorophyll synthesis, respiration, and photosynthesis

Iron deficiency symptoms..interveinal chlorosis on younger leaves (immobile)

Boron

Boron is used in DNA synthesis, cell division, flowering, and fruiting

Boron deficiency symptoms..thick and chlorotic young leaves, death or malfunction of terminal bud

Molybdenum

Molybdenum exists in very tiny amounts in plants

Molybdenum is used in protein synthesis and nitrogen fixation

Molybdenum deficiency symptoms..pale yellow leaves that roll up

Manganese

Manganese is used by plants in chlorophyll synthesis and enzymes

Manganese deficiency symptoms..chlorosis with necrotic spots

Zinc

Zinc is used in enzyme activation and auxin production

Zinc deficiency symptoms..reduced leaf size and internode length, interveinal chlorosis, and branch dieback

Zinc deficiencies are common in high phosphorous soils

Copper

Copper is involved in chlorophyll synthesis

Copper deficiency symptoms..interveinal chlorosis, terminal bud death, stunting

Chlorine

Chlorine plays a role in root development and electron transport

Deficiency in chlorine is rare due to deposition by precipitation and its presence in fertilizer as an impurity

Chlorine deficiency symptoms..stunting, necrosis, chlorosis, and wilting

Important Takeaways

Symptoms of nutrient deficiency can be very extreme or mild. These symptoms are a direct result of malfunction in the plant.

Many nutrients are involved in creating chlorophyll or photosynthesizing

Some nutrients are mobile in plants, so symptoms appear on older leaves first (N, P, K, Mg)

Other nutrients are immobile in plants, so symptoms appear on new leaves first (Fe, Cu, Mn, and Zn)

Many nutrients are taken up as ions.

Organic matter binds ions and release them as a result of microbes, leading to a continuous source of nutrients

Micronutrients can be toxic in large quantities and can also compete with each other (for example, copper in tomato fields can cause iron deficiency)

Fertilization

Different plants require different fertilization at different stages of development.

• Corn and potatoes are heavy feeders

• Leafy greens required high nitrogen inputs

• Root vegetables require high potassium inputs

Nutrients can impact susceptibility to pathogens

• Too much nitrogen can make fruit trees susceptible to fire blight due to lots of new, green tissues

• Too little nitrogen can make fruit trees susceptible to fusarium wilt because the plant is unable to adequately protect itself

CEC and soil pH affect nutrient availability

Determining Deficiency

There are three ways to determine a nutrient deficiency in a plant

1. Visual inspection looks for symptoms of specific deficiencies

2. Tissue tests examine nutrients in leaf tissues. The nutrients will vary by tissue age and season and little data exists regarding this method.

3. Soil tests are measured over the entire field. They take soil characteristics into account, such as pH, and provide recommendations.

Three ways to determine nutrient deficiency..visual inspection, tissue test, and soil test

Fertilizers

Fertilizers typically supply nitrogen, potassium, and phosphorous with other micronutrients available in trace amounts as impurities.

Certain plants may need certain fertilizers.

Once applied fertilizers are either used by the plant, lost by leaching, lost by runoff, or are tied up in soil

Organic Fertilizers

Organic fertilizer..comes from living organisms and include plant residues and 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 Fertilizers

Inorganic fertilizers..come 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

Fertilizer application

Complete fertilizers..ones that include nitrogen, potassium, and phosphorus

Incomplete fertilizers..ones that lack one of the big three macronutrients

Fertilizers make be applied as solids, liquid, or gas

Broadcast application..fertilizer is spread uniformly, often before planting, causes much waste

Topdressing application..fertilizer is applied on top of and around the plant

Fertigation application..fertilizer is applied with normal irrigation

Fertilizer is very rarely applied to plant tissues except in cases of micronutrients

Plant Growth Regulators

Plant growth regulators were discovered more than 80 years ago

Seven classes of compounds are currently known that have effects on growth and development

Growth regulators are 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 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

All plant hormones are plant growth regulators, but not all plant growth regulators are hormones

What is the difference between plant hormones and plant growth regulators?..Plant hormones are naturally occurring and plant growth regulators can be natural or synthetic

Requirements for a substance to be called a plant hormone..Must be an endogenous substance and an organic compounds, must regulate physiology in low concentrations, must be transported within a plant, and must not be a vitamin or nutrient.

Plant hormones are divided into growth promoting hormones (auxins, gibberellins, cytokinins, and brassinosteroids) and wounding and stress hormones (ethylene, abscisic acid, and jasmonates).

Auxins

Discovered in 1934

Auxin’s role..cellular elongation, phototropism, apical dominance, sex expression (female), and fruit growth

Gibberellins

First discovered in Japanese rice plants where a fungus was secreting gibberellins, when it was known as foolish seedling disease

Gibberellin’s role..stimulate bolting, stem elongation, and flowering; sex expression (male); dormancy and seed germination; and fruit growth

Cytokinins

First found in coconut milk

Cytokinin’s role..cell division and organ formation, senescence delaying, stomatal opening, and lateral bud break

Abscisic Acid (ABA)

Discovered in 1965

ABA’s role..plant stress signaling (closing stomates during water stress), dormancy, and abscission

Ethylene

Long been known to enhance fruit ripening

Ethylene’s role..fruit ripening and abscission

Brassinosteroids

Discovered in 1972 when the USDA was searching for new plant hormones

Brassinosteroid’s role..increased crop yields, shoot elongation, and stress and disease resistance

Jasmonates

Jasmonate’s role..gives flavor and scent to flowers and herbs and is important for insect, disease, and stress resistance

Propagation

Objectives

Know pros and cons of sexual vs. asexual propagation

Know what factors go into seed production and why it’s important

Understand direct vs. indirect planting

Recognize and discuss 8 asexual propagation methods and vocabulary

Propagation

Propagation..reproduction of new plants from seeds or vegetative parts

Propagation is critical to the horticulture industry and can occur sexually or asexually

Sexual propagation

Seeds are products of pollination and fertilization

Plants may be self pollinated or cross pollinated

A fertilized ovule contains an embryo with a radical and a shoot primordium

An ovule becomes a seed and an ovary becomes fruit

Pros of sexual propagation..easy to ship and plant, inexpensive

Cons of sexual propagation..not always true to type, may or may not be uniform, conditions may not be right for germination, and takes time

Seed Production

Seed production is a large and well-regulated industry. Seeds are produced for home gardeners as well as all agricultural and horticultural production

Location is important in seed production; production often occurs in arid regions to avoid diseases

Harvesting of seeds is more intense than for a typical crop, timing must be exactly when plants are ripe, and weeds must be managed in the field

Seed washing occurs to clean seeds of debris and treatment sometimes occurs

Seeds must be stored in a cool, dry place

Three steps occur for a new cultivar to be certified:

1. A foundation seed is produced by a breeder and agricultural research station

2. A seed becomes registered and is produced by certified growers

3. A seed is certified and sold commercially, as well as being regulated by certifying agencies

Seed packets must contain the cultivar name, country of origin, germination rate, pure seed percentage, other seed percentage, and inert percentage

Seed Viability and Germination

To test seed viability, seeds can be soaked in water, placed on a media with TTC, and cut in half. This destroys the seed.

Seed maturity can be tested using the float test, where viable seed will sink. This does not destroy the seed.

Seed germination rate..test of how many seeds out of 100 or 1000 will germinate

Seed planting

Seeds may be planted directly outdoors (direct) or started indoors (indirect)

Direct planting is easy to handle but seeds may be difficult to sow depending on size. Examples of directly planted crops are corn, peas, lettuce, and beans

Indirect planting involves transplanting. Less time is needed before maturity, but higher costs are associated with it and transport or transplant stress is a common complication. Indirect planting occurs with geraniums, coleus, tomatoes, and peppers.

Hardening off is necessary if seeds are planted indoors and then moved outdoors to prepare them for stress in adjustment to a new environment. This can be done by reducing water, reducing temperature, or reducing fertilization

Primary Seed Dormancy

Physical dormancy..an impervious seed coating

Scarification..breaking the seed coat physically or with acid

In nature a seed coat would be broken by digestion, freezing and thawing, or microbes.

Mechanical dormancy..a seed cost that is permeable but cannot be broken by the plant

Chemical dormancy..germination inhibitors on seed coat

Morphological dormancy..seeds are shed from parent before being fully developed, treated with gibberellic acid

Physiological dormancy..environmental cues such as specific light or temperatures are needed

Stratification..placing seeds in a moist chilling environment (between 32 and 50 degrees)

Dormancy occurs so that germination doesn’t occur in adverse environmental conditions

Germination

Germination can be started before planting and this allows you to have uniformity and overcome site conditions.

Germination prior to planting is done by soaking seeds, using osmotic priming, infusion of chemicals, and gibberellic acid.

Light can impact germination

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

Asexual propagation..propagation by vegetative means, also known as cloning

Asexual propagation can occur through apomixis, cuttings, grafting, budding, layering, separation, division, or tissue culture

Pros of asexual propagation..result is identical to the parent, easier and quicker, avoids juvenility

Cons of asexual propagation..more expensive, viruses pose a threat, storage and handling is more difficult, lack of genetic diversity

Apomixis

Apomixis is not commonly used. Seeds are of maternal origin only and are diploid 2N

Cuttings

Cuttings are the most common means of asexual propagation

Cuttings can be done with stem cuttings, leaf cuttings, leaf bud cuttings, and root cuttings. Not all leaf cuttings can form shoots and root cuttings are not always true to the parent.

Rooting “Hormone”

For all types of cuttings rooting hormones may be used. Most are IBA or NAA, which are both auxins.

Optimal Rooting of Cutting

To encourage rooting in a cutting, there are several conditions to be aware of

• Good environmental conditions and physiology of the parent plant

• Timing; morning is best, for herbaceous plants cuttings should be taken in the spring and for woody plants winter is better

• Preparation of cuttings can including rooting hormone

• Root inducing environment should be ideal including humidity, temperature, and medium

• Fertilization should only occur once roots are formed

• Transpiration should be limited by reducing leaf area, shading cuttings, and/or misting cuttings

Grafting

Grafting connects plant parts to each other

Rootstock..lower portion of the plant with roots

Scion..stem with a bud

For successful grafting plants must be compatible (stay within a species), diameter or rootstock must be equal to or larger than the scion, timing must be correct (the buds are dormant but the plant can still produce callous tissue), and the individual performing it should be experienced.

Grafting can help maintain clones, provide disease resistance, promote self pollination, create novelty plants, repair trees, and decrease time to flower/fruit.

Budding

Budding is similar to grafting but only uses a bud on woody tissue

Layering

In layering roots form on stems while still on the parent plant.

Separation

Separation occurs through natural structures being removed and planting, such as tulip bulbs.

Division

In division plant parts are cut into sections.

Tissue culture

For tissue cultures new plants are obtained from explants from a parent plant

Explants..single cells, pieces of plant, or tissues

Micropropagation is one aspect of plant tissue culture

Micropropagation..multiplication of plants in vitro in sterile conditions

Tissue culture is a four step process:

1. Explant establishment

   1. Explants are placed in vitro in a sterile environment

2. Axillary shoot proliferation

   1. Rapid and continuous shoot production

3. Shoots are rooter

   1. Done in vitro or in a similar way to cuttings

4. Plants are acclimated to ambient conditions through hardening off

Application to Horticulture

Uniformity of material is one of the most important horticultural traits

Time to produce is typically desired to be short

Certain cultivars must be produced asexually to keep their colors

Certain species yield male and female plants with seed production

Many vegetables are produced by seed