Water Quality
The description of the
concentration and species of chemical elements and compounds found in water
that make it suitable or unsuitable for growing plants. Organic and biological
contaminants should also be considered.
Water Quality
Considerations
v
Bicarbonates- natural deposits
v
EC- related to salts, natural or runoff contamination
v
SAR- sodium absorption ration
v
Herbicides- surface water, shallow wells
v
Na, Fe, S, Cl, B, F, NO3- natural deposits, runoff
v
Fertilizer or similar - surface water, shallow wells
v
pH
v
Heavy metals- industrial waste
Water Sampling
v Establish
a relationship with one lab
v Sample
in unused plastic bottles, about 1/2 pint to 1 quart depending on lab
v Run
water at least 1 minute to flush lines before sampling
v Sample
as close to water source as possible
v Fill
bottle as full as possible, try not to have air in top
v Secure
lid, label and send to laboratory as soon as possible
Alkalinity and pH
v Alkalinity
is more important than pH
v Alkalinity
is the ability of water to raise substrate pH
v Related
to the carbonate (CO3--) and bicarbonate (HCO3-)
levels in water (the active ingredients in liming materials)
v pH
is an indication of alkalinity
v water
with relatively high pH and low alkalinity may not affect substrate pH
v Water
with relatively high pH and high alkalinity will increase substrate pH
Alkalinity Continued
v Three
crop factors that affect tolerable water alkalinity levels
1. Length of production cycle
2. Plant-to-substrate ratio
3. pH requirements of the crops
Alkalinity
Continued
Level of Importance of
Production Components
v Water
Alkalinity
v Liming
Material
v Crop
Requirement/Tolerance
v Fertilizer
v Substrate
Managing Alkalinity
v Alkalinity
< 60 ppm no action necessary
v Alkalinity
of 60 - 215 ppm
v Reduce
amount of lime used (the water will supply the lime)
v Use
acid forming fertilizers
v Alkalinity
of > 215 ppm
v Acid
injection (acid converts carbonates to CO2)
v Sulfur
burner
v Adjust
water to pH near 5.8 - 6.0
Managing Alkalinity
Acids to Inject
v Liquids:
v Nitric
available at 61.4% or 67%
v Sulfuric
available at 93% and 35%
v Phosphoric
available at 75% and 85%
v Solid:
v Citric-
more expensive but does not change nutrition program
v Solid/Gas:
v Sulfur
Water Acidification
Acid
75% Phosphoric
85% Phosphoric
93% Sulfuric
50/50% P & S
61% Nitric
Fl. Oz. Acid/
gal of water &
ppm bicarb
0.00012
0.0001
0.000055
0.000077
0.00017
Acid Injection and Fertility
v Acids
need to be taken into consideration in nutrition program:
v Phosphoric
acid- generally adds much more P than needed in nutrition program- problem from
runoff/contamination aspect
v Nitric
acid- adds N which should be taken into account in nutrition program
v Sulfuric
acid- generally adds much more S than needed in nutrition program
Acid Injection - Safety
v Phosphoric-
safest, if washed off quickly usually no burning of skin
v Sulfuric-
if washed off immediately usually minor burning
v Nitric-
burning occurs very quickly
v Always
add acid to water, Never water to acid
Management
Strategies for
Poor Water Quality
Bicarbonates:
v Do not over water
v Use acid or acid forming
cmpds in substrate
v Reduce lime addition
v Use acidic substrate
v Inject acid
Electrical
Conductivity (EC)
v Measure
of total salts
v Expressed
as deciSiemens/m (dS/m)
v EC
< 0.25 dS/m best
v EC
> 1.00 dS/m can lead to problems
EC Continued
v Water
with high EC will add to salts present due to fertilizer
v Acid
injection will increase EC
v Management
for high EC include
v increased
watering (leach out salts)
v Slow
release fertilizer
v Reduced
rate & split application of fertilizers
EC Levels for
VTEM Pour Through
Sensitive Crops
(liquid feed)
Nursery Crops
(liquid feed)
Nursery Crops
(controlled release)
dS/m or mmhos/cm
0.50 - 0.75
0.75 - 1.50
0.20 - 1.00
Management
Strategies for
Poor Water Quality
High Soluble Salts:
v Do
not under water
v Monitor
soluble salts in containers
v Leach
containers
v Reduce
fertilizer rates
v Dilute
bad with good
v Plant
selection
Sodium
v Critical
level is 50 - 100 ppm
v Not
an essential element, presence only contributes to higher EC
v Sodium
interferes with uptake of N, P, Ca, Mg
Sodium Absorption
Ratio
v Na,
Ca and Mg compete for uptake
v Ratio
determines level of problem
v SAR
= [Na+] / (([Ca2+] + [Mg2+])/2)0.5
v SAR
< 10 safe for most field crops
v SAR
< 3 for container production
Management
Strategies for
Poor Water Quality
Sodium Problems:
v Increase
N, K, Ca, Mg but watch EC!
v If
Ca & Mg in water:
v Do
not under water
v Leach
containers
v Microirrigation
(no foliar absorption)
v Dilute
bad with good
v Use
gypsum or lime to flush Na
Management
Strategies for
Poor Water Quality
High Chloride:
v Critical level 70 ppm
v Do not under water
v Leach containers
v Microirrigation (no foliar
absorption)
v Dilute bad with good
Chlorine vs Chloride
v Chlorine
is different than Chloride
v Critical
levels of chlorine in irrigation water are much lower- should be < 10 ppm
Other Elements
v Iron-
< 5 ppm
v Borate-
< 0.5 ppm (1 ppm toxic)
v Manganese-
< 1 ppm
v Zinc-
< 0.3 ppm
v Copper-
< 0.2 ppm
v Fluoride-
usually not a problem with nursery crops
Management
Strategies for
Poor Water Quality
Leaf Residues:
v Irrigate less frequently
v Irrigate when evaporation is
slow
v Microirrigation
v Acid Injection
Reverse Osmosis
v Very
Expensive
v Used
for specialty operations
v Used
for high value crops
v Volume
limited
Recycling
Irrigation Water
v Restricts
movement of contaminated (fertilizers, pesticides) runoff
v Affects
water quality both good and bad
v Conserves
water resources
v Requires
improved managemen