Tools for adjusting irrigation water pH and alkalinity

Tools for adjustingirrigation water

pH and alkalinity

Amy Galford, Water Resources Educator &Steve Bogash, Horticulture Educator

Penn State Extension Cumberland Countyaeg21@psu.edu & smb13@psu.edu717-240-6500

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, aeg21@psu.eduSteve Bogash, smb13@psu.edu717-240-6500