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Tools for adjustingirrigation water
pH and alkalinity
Amy Galford, Water Resources Educator &Steve Bogash, Horticulture Educator
Penn State Extension Cumberland [email protected] & [email protected]
Water Resources Webinar, 2/25/2015
Outline
* Define pH and alkalinity
* Why they matter for irrigation
* Test your irrigation water!
* Options for changing irrigation pH & alkalinity
* Recipes and calculators for acid addition
* Acid injection equipment examples and tips
* Poll questions and Q&A
Water, acids, and bases
H2O + H2O ↔ H3O+ + OH-
Pure water has small equal amounts of H+ and OH-
Solutions with more H+ = “acidic”
Solutions with more OH- = “basic”
American Chemical Society ACS.org
pH is shorthand for H+
Concentration of H+ affects many chemical reactions
Technically pH = - log [H+]
low pH = more acidic high pH = less acidic, more basic
- 1 pH unit = 10 X as acidic + 1 pH unit = 0.1 X as acidic
Small changes in pH are big changes in H+
Examples of pH mathPure water (in a lab – water doesn’t stay this way!)
[H+] = 0.0000001µM = 10-7M (OH- also 10-7µM)
pH = - log (10-7) = 7
Examples of pH mathPure water (in a lab – water doesn’t stay this way!)
[H+] = 0.0000001µM = 10-7M (OH- also 10-7µM)
pH = - log (10-7) = 7
A solution with pH = 4
[H+] = 0.0001µM = 10-4µM
1000 X more acidic than pure water
Examples of pH mathPure water (in a lab – water doesn’t stay this way!)
[H+] = 0.0000001µM = 10-7M (OH- also 10-7µM)
pH = - log (10-7) = 7
A solution with pH = 4
[H+] = 0.0001µM = 10-4µM
1000 X more acidic than pure water
A solution with pH = 10
[H+] = 0.0000000001µM = 10-10µM1/1000 as acidic as pure water
What does all this have to do with irrigation water?
pH affects other chemicals
…naturally found in irrigation water sources
…that we add on purpose (fertilizers, pesticides, disinfectants)
…in irrigation equipment
Many plants do well with slightly acidic irrigation water
Rain
What does all this have to do with irrigation water?
“Ideal” pH usually a range
Depends on your crops and uses
What if we want to change the pH?
Adjust with concentrated acids
But real water sources are more complicated
Alkalinity = buffering capacity relative to acids
Measure of carbonate, bicarbonate, and hydroxide ionsCO3
2- HCO3- OH-
All of these can neutralize acids (H+)
Acids react with the alkalinity before the overall pH changes.
Alkalinity is eliminated by acid as CO2 gas leaves solution.
Water source affects alkalinity
Rocks and soils can contain carbonateLimestone/dolomiteCaCO3 (calcite), MgCO3
High alkalinity wells orstreams
Water source affects alkalinity
Rocks and soils can contain carbonateLimestone/dolomiteCaCO3 (calcite), MgCO3
High alkalinity wells orstreams
“Hardness” = Calcium + Magnesium Often correlated w/ alkalinity but not the same.
Calcite deposits can clog drip irrigation lines.Calcium and magnesium ions can interfere with other products.
Water source affects alkalinity
In ponds, photosynthesis by algae and aquatic plantsduring day uses CO2 or HCO3
-
Respiration by all living things night and day releases CO2
pH and alkalinity vary during the day
What’s in your water? Test!
Tests at a DEP-accredited lab several times per year.pH, alkalinity, nutrients relevant to your cropsbacteria as needed for food safety
More frequent tests with test strips, handheld meters.
Test before and aftertreatment equipment pH adjustmentadding nutrients, fertilizers, pesticides, etc.
When are you irrigating?
When and where are you sampling for water chemistry?
Units – important for calculations
pH – none, cancel (pH units)
Most concentrations mg/L = ppmmilligrams per Liter = “parts per million”
(a Liter of water weighs 1 million milligrams)
sometimes µg/L = ppb = parts per billion
Alkalinity = mixture of ions so hard to write a concentrationOften expressed as “mg/L as CaCO3” or “ppm CaCO3”= as if all due to CaCO3sometimes ppm HCO3
- or meq/L
Options for changing irrigation pH & alkalinity
Explore different water sources
Rain water is acidic
Blend sources
Make chemical adjustments
Next:
Recipes and tools for chemistry adjustment
Irrigation system parts to add chemicals to irrigation water
pH and alkalinity adjustment – acidify
Choose acid based on safety, cost, nutrients in acid, organic
Use tools to estimate acid to addEstimates help with acid choiceAlways check actual results with small batches you
allow to equlibrate
Usually remove alkalinity along the way to reducing pH
Adjust pH for general irrigation water
After adding fertilizers or pesticides, test pH again
pH and alkalinity adjustment – increase pH
If water source is too acidic, raise pH with
CaCO3 (calcium carbonate, calcite, limestone)
KHCO3 (potassium bicarbonate)
Recipes and calculatorsReference tables, e.g., NC State Extension:
NC State, Purdue, Univ of NH Extension → AlkCalc online toolhttp://extension.unh.edu/Agric/AGGHFL/alk_calc.cfm
AlkCalc online tool
AlkCalc online tool
AlkCalc online tool
WATCH UNITS!
AlkCalc online tool
Usually target pH, alkalinity reduced
AlkCalc online toolChoose
specific acid or
“all acid types”
Citric Acid powder another choice not included (organic)
AlkCalc online tool - example
DATA (from Penn State AASL)
AlkCalc online tool - example
not zero
Injectors for acids (or bases)
left: proportional injectorabove: peristaltic pump (part rotates to squeeze fluid through tubing)
Injectors for acids (or bases)
Building for protection. Black = filter for particles
Also see 2014 webinar on home garden irrigation systems
Safety notes
Can’t ID chemicals by looksclear/pale yellow liquid?white powder?
Original labelled containersor make labels
Mark date opened
Secondary containers to catchspills and leaks
Store chemical types separately
Safety notes
Wear protective eyewear, glove, aprons
Lock out children, pets, livestock
Keep a binder/folder ofsafety data sheets
To dilute an acid, add acid to water slowlydissipate heatany splashes will be mostly water
Summary
Small changes in pH are big changes in H+
pH affects chemistry of nutrients and other chemicals
Source water chemistry varies (future webinar) – Test!
Alkalinity buffers pH, affecting pH adjustments
Use tools to estimate acid requirements; truthcheck
Calibrate injection equipment and use safely
Resources that will be posted to thePenn State Extension water webinar site soon:
Archive of webinar and PDF of this presentation
Link to AlkCalc site http://extension.unh.edu/Agric/AGGHFL/alk_calc.cfm
Link to Penn State Extension Water for Agriculture pagehttp://extension.psu.edu/natural-resources/water/agriculture
Amy Galford, [email protected] Bogash, [email protected]
