Managing Water Quality
in Growing Media
David Wm. Reed
Department of Horticultural Sciences
Texas A&M University
Factors That Impact Water Quality in Growing Media
Factors That Impact Water Quality in Growing Media
Factors That Impact Water Quality in Growing Media
Factors That Impact Water Quality in Growing Media
Factors That Impact Water Quality in Growing Media
Factors That Impact Water Quality in Growing Media
Factors That Impact Water Quality in Growing Media
Factors That Impact Water Quality in Growing Media
Factors That Impact Water Quality in Growing Media
Factors That Impact Water Quality in Growing Media
Factors That Impact Water
Quality in Growing Media
 Irrigation
Water Quality
Factors That Impact Water Quality in Growing Media
Irrigation Water Quality
 Chemical
Properties
 pH
 alkalinity
 EC
 SAR
 Individual
Soluble Salts
 Water Treatment Methods
Growing Medium EC and pH
Saturated
Paste
1:2
Dilution
Pour
Through
5.5-6.5
5.5-6.5
pH
All Plants
5.5-6.5
EC dS/m
Young Plants
1-2
0.5-0.9
Established
Plants
2-3
0.8-1.2
3-5
(from Lang 1996)
Irrigation Water Alkalinity Limits
Minimum Maximum
ppm
Plugs and/or seedlings
38
Small pots/shallow flats 38
4" to 5" pots/deep flats
38
6” pots/long term crops
63
meq/l
0.75
0.75
0.75
1.25
ppm meq/l
66 1.3
86 1.7
106 2.1
131 2.6
(from Bailey 1996)
Irrigation Water Critical Limits
Minimum
Maximum
pH
5.5
7.0
EC (dS/m)
0.2
0.8
ppm
Alkalinity
40
160
Ca
25
75
Mg
10
30
S
0
40
Na
0
20
Cl
0
20
Fe
0
1
Zn
0
0.5
B
0
0.1
Cu
0
0.1
Mo
0
0.1
F
0
0.1
(from Biernbaum 1994)
Plant Nutrient Requirements Supplied
by Irrigation Water
Nutrient
S
Minimum ppm
To Supply Plant
Requirements
20-30 ppm
Ca
40 ppm
Mg
20 ppm
B
0.3 ppm
Sulfur Supplied by Irrigation Water
20-30 ppm supplies most plant’s requirement(from Reddy 1996)
Irrigation Water Quality

Water Treatment Methods
Water Purification Methods
Reverse
Osmosis
Water
Softener
Alkalinity
(carbonates)
X
Total Salts
X
Sodium
X
Chloride
X
Iron
X
Boron
X
Fluoride
X
Manganese
X
X
Copper
X
X
Calcium
X
X
Sulfate
X
Acid
Injection
Aeration/
Oxidation
Activated
Carbon/Al
X
X
X
X
X
X
X
(from Reed 1996)
Reverse Osmosis Unit
Reverse Osmosis Water Purification
To Decrease Salts
Pretreatments:
1) Polymer injection
2) Depth Filter
3) Charcoal Filter
4) Ion Exchange
Purification System:
Reverse Osmosis
to coagulate due to high SDI
to remove coagulated particles
to remove municipal chlorine
to remove residual polymer
using polyamide membranes
(pH resistant, chlorine sensitive)
Production Capacity
Purified Water
5,760 gallons per day
Blended Water (40/60) 14,400 gallons per day
Blend to EC of
0.75 dS/m (approx. 500 ppm)
(from Reed 1996)
Reverse Osmosis Water Purification
To Decrease Salts
Costs
Lease and Service
$900 per month
Water (1.09/1,000)
$700 per month
Electricity
$200 per month
Total
$1800 per month
Purified Water Cost 1 cent per gallon
Blended Water Costs 0.4 cents per gallon
Production Space Irrigated
80,000 to 135,000 square foot of 6-inch production space
(at 12-20 oz/6”pot/day at 0.9 sq. ft. space/6”pot)
Purified Water Used For
Salt sensitive foliage plants and mist propagation
(from Reed 1996)
Acid Injection
80% Neutralization to Approx. pH 5.8
Acid
Fluid ounce of acid
per 1,000 of water,
for each meq
of alkalinity
Nitric (67%)
Phosphoric (75%)
Sulfuric (35%)
6.78
8.30
11.00
ppm
per oz. per
1,000 gal
water
1.64 N
2.88 P
1.14 S
(from Bailey 1996)
Fertilizer Program
 Soluble
Liquid Feed
 Granular Incorporation
 Controlled Release Incorporation
Factors That Impact Water Quality in Growing Media
EC of Soluble Fertilizers & Water Quality
(from Peterson 1996)
Fertility & Salt Stratification in the Root Zone
Subirrigation – New Guinea Impatiens ‘Barbados’
(from Kent & Reed 1996)
Irrigation Method
 Top-Watering
vs. Subirrigation
 Vertical Stratification of Salts
 Evaporation from Surface
 Leaching Fraction
Factors That Impact Water Quality in Growing Media
Vertical Stratification of Soluble Salts
Salt Stratification in the Root Zone with Different
Irrigation Methods
(from Molitor, 1990, Warncke & Krauskopf 1983)
Evaporation from Surface
Causes Vertical Stratification of Salts
Effect of Evaporation on Salt Stratification
Poinsettia ‘Gutbier V-14 Glory’
(from Argo and Biernbaum 1995
Warncke & Krauskopf 1983)
Effect of Evaporation on Salt Stratification
Poinsettia ‘Gutbier V-14 Glory’
(from Argo and Biernbaum 1995
Warncke & Krauskopf 1983)
Vertical Stratification of Soluble Salts
and
Root Distribution
Salt Stratification & Root Distribution
Spathiphyllum in subirrigation
(from Kent & Reed, unpubl;
Warncke & Krauskopf 1983)
Track EC to Monitor
 Soluble Salt Accumulation
 Over Fertilization
 Minimum Fertility Level
Caution: DO NOT sample the top layer
Graphical Tracking: EC
Crop: ______________________
Leaching Fraction
and
Soluble Salt Accumulation
Leaching in Top-Watering Vs. Subirrigation
Leaching Fraction in Top-Watering
Low LF
LF ~ 0.3-0.4
High LF
LF @ ECw / (5(ECe(desired)-ECw))
Effect of Leaching Fraction on Medium EC
Poinsettia ‘V-14 Glory’
0 LF
6
0.15 LF
5
EC 4
dS/m
3
sat.
2
ext.
0.35 LF
0.55 LF
1
0
2
4
6
8
10
12
14
16
Week
(from Yelanich and Biernbaum 1993,
Warncke & Krauskopf 1983)
Top Layer Salts and Wilting Upon Irrigation
Especially Critical in Subirrigation
(from Todd & Reed 1998)
Leaching & Salt Removal From Media
New Guinea Impatiens ‘Blazon’ in Subirrigation
20
15
10
EC
dS/m
5
0
1
2 3
4
Times Leached
5
6
0
2
4
6
8
10
14
18
mM CaCl2 + NaCl
(from Todd & Reed 1998)
Determination of
Soluble Salt Toxicity Limits
“Shoot Gun” Approach
Plant Response to 24 Texas Water Sources
1.1
0.9
0.3
1.0
0.5 0.2
0.3 0.7
0.8
0.8
0.1 0.5
0.1
0.5
0.2
0.4
1.2
(from Kent & Reed unpubl)
Growth Versus EC with 24 Water Sources
Vinca ‘Apricot Delight’ Grown in Subirrigation
(from Kent & Reed unpubl)
Growth Versus EC with 24 Water Sources
Vinca ‘Apricot Delight’ Grown in Subirrigation
(from Kent & Reed unpubl)
Growth Versus EC with 24 Water Sources
Vinca ‘Apricot Delight’ Grown in Subirrigation
(from Kent & Reed unpubl)
Growth Versus Na + Cl with 24 Water Sources
Vinca ‘Apricot Delight’ Grown in Subirrigation
(from Kent & Reed unpubl)
Determination of
Soluble Salt Toxicity Limits
Studies on Individual Salts
(cation + anion combinations)
Toxicity Limits to Sodium Bicarbonate
Rose
0 mM
2.5 mM
7.5 mM
Chrysanthemum
0 mM
5 mM
10 mM
2.5 mM
7.5 mM
10 mM
5 mM
(from Valdez, PhD)
Predicted NaHCO3 Toxicity Limit as a
Function of Chlorosis
Rose
SPAD
Index
decrease
Mum
Vinca
Hibiscus
‘Mango
Breeze’
Hibiscus
‘Bimini
Breeze’
Predicted mM NaHCO3
10%
0.8
3.2
6.0
2.1
4.2
20%
1.7
4.8
7.4
4.2
8.5
30%
2.8
6.1
8.4
6.3
12.7
40%
4.2
7.2
9.3
8.4
16.8
(from Valdez, PhD)
Determination of
Soluble Salt Toxicity Limits
Studies on Individual Salts
(cation + anion combinations)
Problem With This Approach
Do not know if the effect is due to the
cation or the anion
Determination of
Soluble Salt Toxicity Limits
Separation of Anion and Cation
Effects Using Mixture Experiments
Mixture Experiment
Design
X
1:0:0
Pure
blends
Tertiary
blends
Centroid
2/3:1/6:1/6
Binary
blends
½:½:0
1/3:1/3:1/3
1/6:2/3:1/6
½:0:½
1/6:1/6:2/3
Z
0:0:1
Y
0:1:0
0:½:½
Shoot Dry Mass (g)
Mixture-Amount Experiments to Separate the
Na+ and HCO3- Effect in Sodium Bicarbonate
Na+ tox./K+ def.=-19%
0 mM HCO3
HCO3- effect=-15%
7.5 mM HCO3
(from Valdez, PhD)
Binary Mixture Experiments to Separate the
Na+ and HCO3- Effect in Sodium Bicarbonate
Shoot Dry Mass (g)
2.5 mM total binary mixture
6.0
0
0
HCO
3
5.0
0
4.0
0
2.5 HCO33.0
0
2.0
0
1.0
0 +
Na
0.00 0.25
+
K
1.00 0.75
Na+=-19%
HCO3-=-19%
0.50
0.50
0.75
0.25
1.00
0.00
Proportion of K+ and Na+
(from Valdez, PhD)
Mixture-Amount Experiments To Separate
Chloride, Bicarbonate and Sulfate Effects
(from Kent & Reed unpubl)
Separation of Chloride, Bicarbonate and Sulfate Effects
with Mixture-Amount Experiments
Vinca ‘Pacifica Red’ in Subirrigation
Cation = Na
HCO3
SO4
Cation = Na
Cl
30 meq/l
HCO3
SO4
Cation = Na
Cl
45 meq/l
HCO3
SO4
Cl
60 meq/l
(from Kent & Reed unpubl)
Mixture-Amount Experiments To Separate
Chloride, Bicarbonate and Sulfate Effects
Vinca ‘Pacifica Red’ in Subirrigation
Cation = Na
HCO3
SO4
Cation = Na
Cl
30 meq/l
(1,700 to 2,500 ppm)
HCO3
SO4
Cation = Na
Cl
45 meq/l
(2,300 to 3,400 ppm)
HCO3
SO4
Cl
60 meq/l
(2,800 to 4,400 ppm)
(from Kent & Reed unpubl)
Thanks
EC of Soluble Fertilizers & Water Quality
4
EC dS/m
3
20-20-20
15-10-30
2
1
0
0
100
200
300
Soluble Fertilizer ppm N
400
Separation of Sodium and Bicarbonate Effect
Using Mixture Experiments
5.5
4.5
g
shoot 3.5
mass
Na+ tox./K+ def.=-19%
2.5
HCO3- effect=-15%
Rb+7.5mM
K+ 0 mM
Na+7.5mM
Na+ 0 mM
Rb+ 0 mM
(from Valdez,
Ph.D. dissertation)
K+ 7.5mM
Leaching & Salt Removal From Media
New Guinea Impatiens ‘Illusion’ in Subirrigation
20
15
10 EC dS/m
5
0
1
2
3 4
Times Leached
5
6
0
2
4
18
10 14
6 8
mM CaCl2 + NaCl
(from Todd & Reed 1998)