Physical Characteristics of Soilless Substrates Andrew G. Ristvey Extension Specialist Commercial Horticulture University of Maryland Extension Wye Research

Physical Characteristics of Physical Characteristics of Soilless SubstratesSoilless Substrates

Andrew G. Ristvey Andrew G. Ristvey Extension Specialist Commercial HorticultureExtension Specialist Commercial Horticulture

University of Maryland ExtensionUniversity of Maryland Extension

Wye Research and Education CenterWye Research and Education CenterCollege of Agriculture and Natural College of Agriculture and Natural

ResourcesResourcesUniversity of MarylandUniversity of Maryland

Substrate Technology, Water and Mineral Nutrition in Protected Agriculture

WorkshopDay 1 Topic 2

Objectives for this topic include:

Review soilless substrate physical properties

Relate those factors to air and water availability

Evaluations for physical properties

Smarter Substrate ManagementSmarter Substrate Management

Soils vs Soilless SubstratesWhat are the important physical differences between

soils and soilless substrates?Parent materials or components Particle size

Porosity Air and water availability

ACE / NETC 99

Perlite

Soilless Substrates

Composition

Particle Size = Pore

USDA System

Soils

Texture

Structure

Pinebark

Particle Size

Soilless Substrates Soilless Substrates Physical Properties Three Phases of Growing Media by volume

45% Solid (matrix)

15 - 45%Water

10 - 40% Air

Solid (matrix) – 33 to 50%

Total Pore Space

Water % Air %

Matrix Component Porosity:determines the ratio between

Liquid (water) – 15 to 45%Gas (air) – 10 to 40%

Water % + Air % = Total Pore Space

• Highly Variable– Physical properties

• Very porous • Leach very easily • Various combinations

• Plant Available Water – the % volume of water

that plants can retrieve

PinebarkPerlite

• Peat Moss• Pine bark• Perlite• Coir• Rice Hulls• Shredded palm leaves

and other organics• Sand• Gravel• Vermiculite

Variability of Components

Component StructureComponent Structure

(Handreck & Black, 1994)

Electron micrograph of Sphagnum Peat

Typical Substrates Utilized in Costa Rica

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

Physical PropertiesParticle Size and Composition: Their affect on:

Porosity: Air and Water AvailabilityPorosity: Air and Water Availability

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

PoresPores 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

Porosity:

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)

water

air

Soil particles

Components Affect AFP and WHCwater

air

Soil particles

• 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

• Pore size affects WHC and AFP

Physical Properties : Pore Size

Components Affect AFP and WHC

Soilless SubstratesSoilless SubstratesImportant 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 AFPW1 = Saturated container media

W2 = Drained container (several hours later)

W3 = Volume of Substrate

W4 = Weight of Container

W5 = Weight of Dry Media

% AFP =W1

W3 –

SaturationAFP

Total Volume

X 100– W2

W4

WHC = % W2

W3X 100– (W5 + W4)

Substrate ManagementSubstrate Management







Objectives for this topic include:

Composting and aging

Storage of substrates

Handling of substrates

Smarter Substrate ManagementSmarter Substrate Management

Composting and Aging 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


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 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 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 : 13. Degradation of organic material and increase Cation Exchange

Capacity

Composting Composting and Aging and Aging

Microorganisms

The Aerobic Cycle

http://www.theteggroup.plc.uk/technical_library/microbiology_of_invessel_composting


Composting and Aging 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

Lignin

Cellulose

Composting and Aging 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

But first…Prevention!

is crucial to successful plant health management

Smarter Substrate ManagementSmarter Substrate ManagementThere 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

Storage of SubstratesStorage of Substrates


Storage – high and dry?

Potting- do not compress substrate- water the plant into pot

What else? Handling Watering Age


Practical Examination for SubstratesPractical 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 handlingSubstrate Re-use and handling

Irrigation in Protected Environments:Irrigation in Protected Environments:Checking Irrigation System EfficiencyChecking Irrigation System Efficiency

John Lea-Cox and David RossJohn Lea-Cox and David RossNursery Extension Specialist / Extension EngineerNursery Extension Specialist / Extension Engineer


College of Agriculture and Natural ResourcesCollege of Agriculture and Natural ResourcesUniversity of MarylandUniversity of Maryland

Substrate Technology, Water and Mineral Nutrition in Protected Agriculture Workshop

Day 2 Topic 4

Overhead Irrigation SystemsOverhead Irrigation Systems

The pros and cons of overhead irrigation systems.

Pros

1. Easy management

2. Lower labor costs

3. Less infrastructure

Cons

1. Efficiency low - depending

2. Larger volumes needed

3. Higher pressures needed

Micro Irrigation SystemsMicro Irrigation Systems

The pros and cons of microirrigation systems.

Pros

1. Higher Efficiency

2. Less volume needed

3. Lower pressures

4. Less waste

Cons

1. Greater management

2. Higher costs – more specialized equipment needed

3. Potential Higher labor costs

ACE / NETC 99

Irrigation Audits Irrigation Audits SummaryIs 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.

Pressure Check

Installed or Portable Pressure Gauges

Pressure Check

Filter Pump

Laterals – drip or sprinkler Pressure Gauge

Pressure variation in a LateralFor 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 psiAverage of 50

psi 45 psi

Too High Correct Pressure

Too Low

Nozzle Pressure versus Water Distribution Pattern

Pressure affects Application Pattern

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

Nozzle (new) specs for water discharge at a given pressure.

RainBird 14DH

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

Note changes in gpm & radius for changes in Size.

RainBird 14DH

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.


Catch can – top left

Calibrated measuring container – bottom left/ top right


Audit Kit

Irrigation Association Education Foundation

www.iaef.org

Application Uniformity CheckCatch cans - use 16 or more.

Do audit to sample application uniformity several places.


Irrigation Lateral

Production Bed – Hoop House

Catch cans

Must run all laterals that cover catch area.

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

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!

Irrigation in Protected EnvironmentsIrrigation in Protected EnvironmentsPlant/Substrate Relations Plant/Substrate Relations







Smarter Irrigation ManagementSmarter 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 Container Size and Water Holding CapacityWater Holding Capacity

Given the same substrate

Squat containers hold more water

Given the same volume

Moisture/air gradient – capillary action

AFP and WHC based on Container Size

Adapted from A Grower’s Guide to Water, Media, & Nutrition for Greenhouse Crops, Ed. David Wm. Reed, 1996.

% Water

% Solid

% Air0

10

20

30

40

50

60

70

80

90

100

6 inch 4 inch 48 cell 512 cell

Plant Available WaterPlant 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


Electron micrograph of Sphagnum Peat


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 plantsEven 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 substrateDivided into:Easily Available Water and Water Buffer Capacity




0 -5 -100

100

Vol

ume

% (

20 c

m h

igh

pot)

-1

Suction applied (kPa)

Solids

Air

Total Pore Space

Water

AirAir Filled Porosity(at container capacity)

Readily available water

Easily Available Buffer capacity

Unavailable Water (progressively)

set points

7 kPa = 1 PSI

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).

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

Finding Plant Available Water

100%Perlite

80 Pine Bark : 20 Peat

100%Coir

100%Pine Bark

80 Peat: 20 Perlite

Pressure (kPa)

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%)

Results – Physical Properties (5cm columns)

Determination of Leaching FractionDetermination of Leaching Fraction

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Physical Characteristics of Soilless Substrates Andrew G. Ristvey Extension Specialist Commercial Horticulture University of Maryland Extension Wye Research