Physical Characteristics of

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Substrate Technology, Water and Mineral Nutrition
in Protected Agriculture Workshop
Day 1 Topic 2
Physical Characteristics of Soilless Substrates
Andrew G. Ristvey Extension Specialist
Commercial Horticulture
University of Maryland Extension Wye Research
and Education Center College of Agriculture and
Natural Resources University of Maryland
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Smarter Substrate Management

• Objectives for this topic include
• Review soilless substrate physical properties
• Relate those factors to air and water
  availability
• Evaluations for physical properties

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Soils vs Soilless Substrates
What are the important physical differences
between soils and soilless substrates?
Parent materials or components
Particle size
Porosity
Air and water availability
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Particle Size
Soils

• Soilless Substrates
• Composition
• Particle Size Pore

• Texture
• Structure

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Soilless Substrates Physical Properties

• Three Phases of Growing Media by volume

Solid (matrix) 33 to 50
Liquid (water) 15 to 45
45 Solid (matrix)
Gas (air) 10 to 40
Water Air Total Pore Space
15 - 45 Water
10 - 40 Air
Matrix Component Porosity
determines the ratio between
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Variability of Components

• Peat Moss
• Pine bark
• Perlite
• Coir
• Rice Hulls
• Shredded palm leaves
• and other organics
• Sand
• Gravel
• Vermiculite

• Highly Variable
• Physical properties
• Very porous
• Leach very easily
• Various combinations
• Plant Available Water
• the volume of water that plants can retrieve

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Component Structure
(Handreck Black, 1994)
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Typical Substrates Utilized in Costa Rica
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Porosity Air and Water Availability

• Physical Properties

Particle Size and Composition Their affect on

• Air-Filled Porosity (AFP)
• Water Holding Capacity (WHC)

• AFP - air in the substrate after irrigation /
  drainage
• WHC water in the substrate after irrigation /
  drainage

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Pores

• When we buy substrate---we are buying pores!
• What else can affect substrate AFP and WHC?
• Handling
• Watering
• Age
• Container geometry
• Potting
• - do not compress substrate
• - water the plant in

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Components Affect AFP and WHC

• Porosity
• Macropores ? Water drain
• through freely
• 
  (lt 4mm)
• Mesopores ? Water at CC
• (1 to 0.5mm)
• Micropores ? Water might
• work as
  buffer
• (0.5 to 0.03mm)
• Ultramicropores ? Water held
• beyond 1.5 Mpa
• (lt0.01mm)

Drzal et al. (1999)
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Components Affect AFP and WHC

• Particle size affects WHC and AFP

• Capillary action

• water tension - water is attracted
• to surfaces with a force large
• enough to support a relatively
• large mass of water against the
• pull' of gravity

• the smaller the particle, the
• more firm the hold

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Components Affect AFP and WHC

• Physical Properties Pore Size

• Pore size affects WHC and AFP

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Soilless Substrates
Important Attributes of Soilless Media

• Recommended physical characteristic values for
  soilless
• substrates, after irrigation and drainage are (
  volume)
• Air-Filled Porosity - 10 to 30 or 20 to 35
  (field test)
• Water Holding Capacity - 45 to 65
• Available water content - 25 to 35
• Unavailable water content - 25 to 35
• Note A substrate with many coarse particles has
  a large air space
• and a relatively low water holding
  capacity.

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Field Test for AFP

• W1 Saturated container media
• W2 Drained container (several hours later)
• W3 Volume of Substrate
• W4 Weight of Container
• W5 Weight of Dry Media

Saturation
W1
W2
AFP
X 100
AFP
W3
W4
Total Volume
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Substrate Technology, Water and Mineral Nutrition
in Protected Agriculture Workshop
Day 1 Topic 3
Substrate Management
Andrew G. Ristvey Extension Specialist
Commercial Horticulture
University of Maryland Extension Wye Research
and Education Center College of Agriculture and
Natural Resources University of Maryland
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Smarter Substrate Management

• Objectives for this topic include
• Composting and aging
• Storage of substrates
• Handling of substrates

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Composting and Aging
Composting is a biological process where complex
organic material is degraded into more basic
organic components at a rate faster than
decomposition would occur naturally. Aerobic
Composting is a thermophilic (generating heat)
process Aging is not composting, because there
is no heat generation
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Composting and Aging

• The process of efficient composting requires
  several ingredients.
• The basic recipe
• A source of organic material
• Microorganisms
• CN ratio of more than 301 this may mean
  the addition of
• a nitrogen or carbon source
• Proper moisture levels 45 to 60 by weight
• Oxygen
• pH stabilizer, if needed

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Composting and Aging
Composting Chemistry The CN Ratio
Materials High in Carbon C/N
Senesced leaves 30-801
straw 40-1001
wood chips or sawdust 100-5001
bark 100-1301
mixed paper 150-2001
newspaper or corrugated cardboard 5601
Materials High in Nitrogen CN
vegetable scraps 15-201
coffee grounds 201
grass clippings 15-251
manure 5-251
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Composting and Aging

• The result of efficient aerobic composting is .
• Generation of Heat 55 Co
• CN Ratio of between 10 and 15 1
• Degradation of organic material and increase
  Cation Exchange Capacity

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Composting and Aging
Microorganisms
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Composting and Aging
The Aerobic Cycle
http//www.theteggroup.plc.uk/technical_library/mi
crobiology_of_invessel_composting
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Composting and Aging

• Cellulose and Lignin
• Why some substrates degrade
• faster than others
• Cellulose is a sugar
• Lignin is a more
• complicated molecule
• and more difficult
• to degrade

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Composting and Aging

• When it goes wrong
• Compounds like alcohols and methane are developed
  in anaerobic composting.
• Weed and pathogens are not destroyed

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Adding Compost to Growing Media

• Consistency can you assure?
• Well/properly composted
• Water Holding capacity Pore Space?
• Nutrient availability
• what is in compost?
• adjust your nutrient management plan?

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Adding Compost to Growing Media

• First, analyze your compost
• All macro and micro nutrients
• How much should be added?
• Base your addition on nutrients, WHC AFP and EC
• Usually no more than 20
• Check your WHC and AFP

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Smarter Substrate Management

• There are three lines of defense against plant
  diseases
• To prevent pathogens from entering the
  production systems
• Create cultural conditions that work for plant
  growth and
• against disease development
• Correctly and timely treat disease problems
  that do arise

But first Prevention! is crucial to successful
plant health management
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Storage of Substrates
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Storage of Substrates

• Storage high and dry?
• Potting
• - do not compress substrate
• - water the plant into pot
• What else?
• Handling
• Watering
• Age

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Storage of Substrates
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Practical Examination for Substrates

• Capillary Force practical experiment
• Particle Distribution Analysis
• Field Porosity and water holding capacity tests
• Question
• Does particle size affect AFP and WHC?

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Substrate Re-use and handling
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Substrate Technology, Water and Mineral Nutrition
in Protected Agriculture Workshop
Day 2 Topic 4
Irrigation in Protected Environments Checking
Irrigation System Efficiency
John Lea-Cox and David Ross Nursery Extension
Specialist / Extension Engineer
University of Maryland Extension College of
Agriculture and Natural Resources University of
Maryland
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Overhead Irrigation Systems
The pros and cons of overhead irrigation systems.

• Cons
• Efficiency low - depending
• Larger volumes needed
• Higher pressures needed

• Pros
• Easy management
• Lower labor costs
• Less infrastructure

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Micro Irrigation Systems
The pros and cons of microirrigation systems.

• Cons
• Greater management
• Higher costs more specialized equipment needed
• Potential Higher labor costs

• Pros
• Higher Efficiency
• Less volume needed
• Lower pressures
• Less waste

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Irrigation Audits
Summary Is your irrigation system working
properly? First, do an inspection repair
problems. Second, check pressures and flow
rates. Third, do a test for uniform
application. Decide on changes to improve
system and water wisely.
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Uniform Water Application?
Applying water uniformly should be goal 1,
particularly for container crops Question -
Where are your dry spots after irrigation? If
none, do you knowingly overwater some plants to
adequately water other plants? How do I check my
irrigation system?
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System Audit Procedure
First, inspect for problems and repair them. 1.
Damaged pipelines and risers 2. Damaged,
clogged, worn, or broken nozzles or drip tubes.
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System Audit Procedure
Second, check pressure and flow rate. 1. What
were the pressures and flow rates of the system
when new? 2. Check pressure at pump, beginning
and end of laterals, and before and after
filters. 3. Check the nozzles for wear and flow
rate. Check drip tubes for clogging.
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Pressure Check
Installed or Portable Pressure Gauges
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Pressure Check
Filter
Pump
Pressure Gauge
Laterals drip or sprinkler
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Pressure variation in a Lateral
For good design, pressure variation from one end
of a lateral to the other should not exceed /-
10 percent of the average lateral design
pressure. Actual variation in lateral is 20.
Average of 50 psi
45 psi
55 psi
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Pressure affects Application Pattern
Correct operating pressure is best! Pressure too
high or too low causes distortion of application
pattern.
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Nozzle Flow Rate
Use a bottle or bucket to catch the water
discharged from the nozzle for one
minute. Measure the volume of water
caught. Convert to gal/min. as in nozzle
chart. Measure nozzle pressure, if possible.
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Nozzle Flow Rate
RainBird 14DH
Nozzle (new) specs for water discharge at a given
pressure.
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Nozzle Flow Rate
RainBird 14DH
Note changes in gpm for changes in PSI.
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Nozzle Wear Check
Use drill bit to check size carefully.
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Nozzle Wear
RainBird 14DH
Note changes in gpm radius for changes in Size.
Wear changes demand on the pump.
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Nozzle Pressure Flow Rate
Lets review the last few slides We checked
nozzle wear, pressure and flow rate. From the
nozzle chart we saw that a different pressure
resulted in a different discharge and wetted
radius. Differences mean non-uniformity!
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Application Uniformity Check
The next step is to check on the application
uniformity of your system. This process uses a
grid pattern of water catch cans to collect
water. A regular pattern of cans is placed on
the ground in the irrigated area.
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Application Uniformity Check
Catch can top left Calibrated measuring
container bottom left/ top right
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Application Uniformity Check
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www.iaef.org
Audit Kit
Irrigation Association Education Foundation
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Application Uniformity Check
Catch cans - use 16 or more.
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Do audit to sample application uniformity several
places.
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Application Uniformity Check
Irrigation Lateral
Catch cans
Production Bed Hoop House
Must run all laterals that cover catch area.
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Lower Quarter Distribution Uniformity, DULQ
Sketch of laterals and sprinklers. Show catch
cans and amounts of water.
List in descending order. Mark smallest quarter.
Average of total and smallest 1/4 .
Divide Average of ¼ by Average of total x 100
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Readings (use 16, 20, 24 or more) 0.32 0.34 0.32
0.34 0.30 0.28 0.25 0.30 0.33 0.30 0.27 0.33 0.36
0.24 0.31 0.37 Total of all 4.96 Average All
0.31 Total small 1/4 1.04 Average 1/4
0.26 DULQ 0.26 / 0.31 x 100 84
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Doing the Math easy!
We calculate the Lower Quarter Distribution
Uniformity, DULQ DULQ Avg of smaller 1/4
readings / Avg of all readings x 100 Tells us
how close the lowest (dry) readings are to all
readings. Less than 70-75 percent is not so good.
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Summary
Correct pressure and nozzle/emitter flow rates
are important factors in overall uniformity of a
system. The Lower Quarter Uniformity
Distribution gives us a measure of the uniformity
of application. Check out your system soon!
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Substrate Technology, Water and Mineral Nutrition
in Protected Agriculture Workshop
Day 2 Topic 5
Irrigation in Protected Environments Plant/Substra
te Relations
Andrew G. Ristvey Extension Specialist
Commercial Horticulture
University of Maryland Extension Wye Research
and Education Center College of Agriculture and
Natural Resources University of Maryland
69
Smarter Irrigation Management

• Manage irrigation and substrate water content

• Are we over-watering? Water logging will
• increase the incidence of disease

• Water-use efficiency research at UGA showed
• that during a 6 week trial, Vinca
  (Catharanthus
• roseus) could be grown with liter of water
• without reduction in mass or quality

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• Why dont we use soil in containers?
• Key reason too many fine particles, which
  leads to waterlogging
• Also, bottom of container creates a barrier to
  drainage resulting in a perched
  water table
• The smaller the particle size, the higher the
  perched table
• Soilless substrates degrade in time and
  act like soils

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Container Size and Water Holding Capacity
Given the same substrate
Given the same volume
Moisture/air gradient capillary action
Squat containers hold more water
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AFP and WHC based on Container Size
Water
Solid
Air
Adapted from A Growers Guide to Water, Media,
Nutrition for Greenhouse Crops, Ed. David Wm.
Reed, 1996.
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Plant Available Water

• Soils and substrates have the ability to hold
  and release water
• Some water is available for the plants
• Some water is not available for the plants
• even though the substrate or soil may seem moist
• Why?
• Recall our lesson about particle size and water
  attraction

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Plant Available Water
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Plant Available Water

• Soils and substrates have the ability to hold
  and release water
• Some water is available for the plants
• Some water is not available for the plants
• Even though the substrate or soil may seem moist
• Why?
• Recall our lesson about particle size water
  attraction
• Plant Available Water is the water that held by
  the soil or substrate
• Divided into
• Easily Available Water and Water Buffer
  Capacity

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Plant Available Water
(Handreck Black, 1994)
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Water
Easily Available
Buffer capacity
Readily available water
(Handreck Black, 1994)
7 kPa 1 PSI
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Finding Plant Available Water

• Desorption curves generated using a custom-built
  desorption table using 5 and 20cm long Ech2O
  capacitance sensors.

• Ten columns were
• simultaneously
• desorbed for each
• substrate (n30).

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Finding Plant Available Water

• Each column was packed by
• slowly adding and settling the
• substrate with water
• Each column had a
• capacitance probe sealed into
• the top polycarbonate lid,
• positioned centrally and
• vertically down the column
• Once sealed, each column was slowly hydrated over
  6 hours to gradually force the interstitial air
  out of the substrate

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Finding Plant Available Water

• Positive gas pressure was incrementally applied
  at 1, 2, 4, 6, 8, 10, 20, 40, 60, 80 and 100
  kPa

• The volume of water expressed
• at each pressure increment was
• measured for each column

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Results Physical Properties (5cm columns)
100 Perlite 80 Pine Bark 20 Peat 100 Coir 100 Pine Bark 80 Peat 20 Perlite
Pressure (kPa) Distribution of Water () Distribution of Water () Distribution of Water () Distribution of Water () Distribution of Water ()
EAW (1 to 5) 36.0 40.0 32.6 34.6 43.7
WBC (5 to 10) 1.2 7.0 2.1 2.2 13.1
PUW ( gt10 ) 62.8 53.0 65.3 63.2 34.1
Total volume of the 5-cm column 722 mL. Note that CC TP - AS. Use CC values to interconvert data. An additional 9.1 water was expressed from this substrate between 10 and 60 kPa (to total 100) Total volume of the 5-cm column 722 mL. Note that CC TP - AS. Use CC values to interconvert data. An additional 9.1 water was expressed from this substrate between 10 and 60 kPa (to total 100) Total volume of the 5-cm column 722 mL. Note that CC TP - AS. Use CC values to interconvert data. An additional 9.1 water was expressed from this substrate between 10 and 60 kPa (to total 100) Total volume of the 5-cm column 722 mL. Note that CC TP - AS. Use CC values to interconvert data. An additional 9.1 water was expressed from this substrate between 10 and 60 kPa (to total 100) Total volume of the 5-cm column 722 mL. Note that CC TP - AS. Use CC values to interconvert data. An additional 9.1 water was expressed from this substrate between 10 and 60 kPa (to total 100) Total volume of the 5-cm column 722 mL. Note that CC TP - AS. Use CC values to interconvert data. An additional 9.1 water was expressed from this substrate between 10 and 60 kPa (to total 100) Total volume of the 5-cm column 722 mL. Note that CC TP - AS. Use CC values to interconvert data. An additional 9.1 water was expressed from this substrate between 10 and 60 kPa (to total 100)
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Determination of Leaching Fraction
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Substrate Technology, Water and Mineral Nutrition
in Protected Agriculture Workshop
Day 3 Topic 9
Knowledge Center - Access to Online Resources
Andrew G. Ristvey Extension Specialist
Commercial Horticulture
University of Maryland Extension Wye Research
and Education Center College of Agriculture and
Natural Resources University of Maryland
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