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
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
Soils vs Soilless Substrates
What are the important physical differences between
soils and soilless substrates?
Parent materials or components
Porosity
Particle size
Air and water availability
Particle Size
Soils
Soilless Substrates
 Composition

Particle Size = Pore
Perlite
Pinebark
USDA
System
 Texture
Structure
ACE / NETC 99
Soilless Substrates Physical Properties
 Three Phases of Growing Media by volume
Solid (matrix) – 33 to 50%
Liquid (water) – 15 to 45%
45% Solid
Gas (air) – 10 to 40%
(matrix)
Water % + Air % =
Total Pore Space
Matrix Component Porosity:
determines the ratio between
Water %
10 - 40%
Air
Air %
Total Pore Space
15 - 45%
Water
Variability of Components
• Highly Variable
– Physical properties
• Very porous
• Leach very easily
• Various combinations
• Plant Available Water
– the % volume of water
that plants can retrieve
• Peat Moss
Perlite
• Pinebark
Pine bark
• Perlite
• Coir
• Rice Hulls
• Shredded palm leaves
and other organics
• Sand
• Gravel
• Vermiculite
Component Structure
Electron micrograph of Sphagnum Peat
(Handreck & Black, 1994)
Typical Substrates Utilized in
Costa Rica
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
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
Components Affect AFP and WHC
Porosity:
water
Macropores
 Water drain
through freely
(< 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
(<0.01mm)
Drzal et al. (1999)
air
water
air
Soil particles
Soil
particles
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
Components Affect AFP and WHC
 Physical Properties : Pore Size
• Pore size affects WHC and AFP
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.
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
% AFP =
WHC = %
W1 – W2
Saturation
AFP
X 100
W3 – W4
W2 – (W5 + W4)
W3
X 100
Total Volume
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
Smarter Substrate Management
Objectives for this topic include:
 Composting and aging
 Storage of substrates
 Handling of substrates
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
Composting and Aging
The process of efficient composting requires several ingredients.
The basic recipe:
1.
A source of organic material
2.
Microorganisms
3.
C:N ratio of more than 30:1 – this may mean the addition of
a nitrogen or carbon source
4.
Proper moisture levels – 45 to 60% by weight
5.
Oxygen
6.
pH stabilizer, if needed
Composting and Aging
Composting Chemistry: The C:N Ratio
Materials High in Carbon
C/N*
Senesced leaves
30-80:1
straw
40-100:1
wood chips or sawdust
100-500:1
bark
100-130:1
mixed paper
150-200:1
newspaper or corrugated
cardboard
560:1
Materials High in Nitrogen
C:N*
vegetable scraps
15-20:1
coffee grounds
20:1
grass clippings
15-25:1
manure
5-25:1
Composting and Aging
The result of efficient aerobic composting is .
1. Generation of Heat ≈ 55 Co
2. C:N Ratio of between 10 and 15 : 1
3. Degradation of organic material and increase Cation Exchange
Capacity
Composting
and Aging
Microorganisms
Composting and Aging
The Aerobic Cycle
http://www.theteggroup.plc.uk/technical_library/microbiology_of_invessel_composting
Composting and Aging
Cellulose and Lignin…
Why some substrates degrade
faster than others
1. Cellulose is a sugar
2. Lignin is a more
complicated molecule
and more difficult
to degrade
Cellulose
Lignin
Composting and Aging
When it goes wrong…
1. Compounds like alcohols and methane are developed
in anaerobic composting.
2. Weed and pathogens are not destroyed
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?
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
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
Storage of Substrates
Storage of Substrates
 Storage – high and dry?
 Potting
- do not compress substrate
- water the plant into pot
 What else?
 Handling
 Watering
 Age
Storage of Substrates
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?
Substrate Re-use and handling
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
Overhead Irrigation Systems
The pros and cons of overhead irrigation systems.
Cons
Pros
1.
Easy management
1.
Efficiency low - depending
2.
Lower labor costs
2.
Larger volumes needed
3.
Less infrastructure
3.
Higher pressures needed
Micro Irrigation Systems
The pros and cons of microirrigation systems.
Pros
Cons
1. Higher Efficiency
1. Greater management
2. Less volume needed
3. Lower pressures
2. Higher costs – more
specialized equipment
needed
4. Less waste
3. Potential Higher labor costs
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.
ACE / NETC 99
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?
ACE / NETC 99
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.
ACE / NETC 99
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.
ACE / NETC 99
Pressure Check
Installed or Portable
Pressure Gauges
Pressure Check
Filter
Laterals – drip or sprinkler
Pump
Pressure
Gauge
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%.
55 psi
Average of 50
psi
45 psi
Pressure affects
Application Pattern
Nozzle Pressure versus Water Distribution Pattern
Too High
Correct Pressure
Too Low
Correct operating pressure is best!
Pressure too high or too low causes
distortion of application pattern.
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.
Nozzle Flow Rate
RainBird
14DH
Nozzle (new) specs
for water
discharge at a
given pressure.
Nozzle
Flow
Rate
RainBird
14DH
Note
changes in
gpm for
changes in
PSI.
Nozzle Wear Check
Use drill bit to check size
carefully.
Nozzle
Wear
RainBird
14DH
Note
changes in
gpm &
radius for
changes in
Size.
Wear changes demand on the pump.
Nozzle Pressure & Flow Rate
Let’s 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!
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.
Application Uniformity Check
Catch can – top left
Calibrated measuring container
– bottom left/ top right
Application Uniformity Check
Audit Kit
Irrigation Association Education Foundation
www.iaef.org
Application Uniformity Check
Catch cans - use 16 or more.
Do audit to sample application uniformity several places.
Application Uniformity Check
Catch
cans
Irrigation Lateral
Production Bed – Hoop House
Must run all laterals that cover catch area.
Lower Quarter
Distribution
Uniformity, DULQ
List in
descending
order. Mark
smallest
quarter.
Average of
total and
smallest
1/4 .
Sketch of laterals
and sprinklers.
Show catch cans and
amounts of water.
[Divide Average of ¼ by
Average of total] x 100
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 %
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.
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!
Substrate Technology, Water and Mineral
Nutrition in Protected Agriculture
Workshop
Day 2 Topic 5
Irrigation in Protected Environments
Plant/Substrate 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
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
Why don’t 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
Container Size and
Water Holding Capacity
Given the same substrate
Given the same volume
Moisture/air gradient – capillary action
Squat containers hold more water
AFP and WHC based on Container Size
100
90
80
70
% Water
60
50
40
% Solid
30
20
10
% Air
0
6 inch
4 inch
48 cell
512 cell
Adapted from A Grower’s Guide to Water, Media, & Nutrition for
Greenhouse Crops, Ed. David Wm. Reed, 1996.
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
Plant Available Water
Electron micrograph of Sphagnum Peat
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
Plant Available Water
(Handreck & Black, 1994)
100
Water
Volume % (20 cm high pot)
Unavailable
Total Pore
Water
(progressively)
Easily
Available
Space
Buffer capacity
Air
Readily available
water
Air
Air Filled Porosity
(at container capacity)
Solids
0
0
-1
(Handreck & Black, 1994)
set points -5
Suction applied (kPa)
7 kPa = 1 PSI
-10
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 (n=30).
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
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
Results – Physical Properties (5cm columns)
100%
Perlite
80 Pine Bark
: 20 Peat
Pressure (kPa)
†
100%
Coir
100%
Pine Bark
80 Peat:
20 Perlite
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
( >10 )
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%)
Determination of Leaching Fraction
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