Monitoring & Maintaining the pH and EC of the Root Environment · 2001-06-27 · Environment...

Monitoring & Maintaining the pH and EC of the Root

Environment

Monitoring & Maintaining the pH and EC of the Root

EnvironmentBill FontenoHorticultural Substrates LaboratoryNC State University

Bill FontenoHorticultural Substrates LaboratoryNC State University

Substrate pHSubstrate pH

Maintaining proper substrate pH will PREVENT most

nutrient problems

Maintaining proper substrate pH will PREVENT most

nutrient problems

4.04.0 4.54.5 5.05.0 5.55.5 6.06.0 6.56.5 7.07.0 7.57.5 8.08.0Nutrient Availability

Nutrient Availability

Affected by changes in

pH

Affected by changes in

pH

NITROGEN

PHOSPHORUS

POTASSIUM

CALCIUM

MAGNESIUM

IRON

MANGANESE

BORON

ZINC

COPPER

Problems Associated With Out-of-Range Substrate pHProblems Associated With Out-of-Range Substrate pH

Low

Toxic: Fe, Mn, Zn, CuToxic: Fe, Mn, Zn, Cu

Deficient: Ca, MgDeficient: Ca, Mg

Sensitive: NH4Sensitive: NH4

Leached: PO4Leached: PO4

High

Deficient: Fe, Mn, Zn, Cu, BDeficient: Fe, Mn, Zn, Cu, B

Substrate pHSubstrate pH

Crops can be divided into three major groups based

on pH needs

Crops can be divided into three major groups based

on pH needs

General Crops Range

General Crops Range

4.04.0 4.54.5 5.05.0 5.55.5 6.06.0 6.56.5 7.07.0 7.57.5 8.08.0

NITROGEN

PHOSPHORUS

POTASSIUM

CALCIUM

MAGNESIUM

IRON

MANGANESE

BORON

ZINC

COPPER

4.04.0 4.54.5 5.05.0 5.55.5 6.06.0 6.56.5 7.07.0 7.57.5 8.08.0

NITROGEN

PHOSPHORUS

POTASSIUM

CALCIUM

MAGNESIUM

IRON

MANGANESE

BORON

ZINC

COPPER

5.4 to 6.85.4 to 6.8

4.04.0 4.54.5 5.05.0 5.55.5 6.06.0 6.56.5 7.07.0 7.57.5 8.08.0

NITROGEN

PHOSPHORUS

POTASSIUM

CALCIUM

MAGNESIUM

IRON

MANGANESE

BORON

ZINC

COPPER

Low pH Range

Low pH Range

4.04.0 4.54.5 5.05.0 5.55.5 6.06.0 6.56.5 7.07.0 7.57.5 8.08.0

NITROGEN

PHOSPHORUS

POTASSIUM

CALCIUM

MAGNESIUM

IRON

MANGANESE

BORON

ZINC

COPPER

5.4 to 5.85.4 to 5.8

4.04.0 4.54.5 5.05.0 5.55.5 6.06.0 6.56.5 7.07.0 7.57.5 8.08.0

NITROGEN

PHOSPHORUS

POTASSIUM

CALCIUM

MAGNESIUM

IRON

MANGANESE

BORON

ZINC

COPPER

High pH Range

High pH Range

4.04.0 4.54.5 5.05.0 5.55.5 6.06.0 6.56.5 7.07.0 7.57.5 8.08.0

NITROGEN

PHOSPHORUS

POTASSIUM

CALCIUM

MAGNESIUM

IRON

MANGANESE

BORON

ZINC

COPPER

6.0 to 6.86.0 to 6.8

4 Forces Affect Substrate pH4 Forces Affect Substrate pH

• Substrate components and

amendments• Substrate components and

amendments

• Irrigation water alkalinity• Irrigation water alkalinity

• Fertilizer acidity / basicity• Fertilizer acidity / basicity

• Plant species being grown• Plant species being grown

Substrate ComponentsSubstrate Components

• Peat moss is very acidic • Peat moss is very acidic

• Perlite & vermiculite have little impact

• Perlite & vermiculite have little impact

• MOST substrates use lime to raise pH

• MOST substrates use lime to raise pH

• A few components (coir fiber) may be alkaline and raise pH

• A few components (coir fiber) may be alkaline and raise pH

Water AlkalinityWater AlkalinitySignificanceSignificance

➲ Alkalinity is “buffering capacity” of water

➲ Alkalinity is “buffering capacity” of water

➲ Major component is bicarbonate ion [HCO3]

-

➲ Major component is bicarbonate ion [HCO3]

-

➲ Alkalinity causes pH to rise over time

➲ Alkalinity causes pH to rise over time

Alkalinity: pH RisesAlkalinity: pH Rises

HCO3

-H+

Carbonic acidCarbonic acid

CO2 OH

-WaterWaterH+

+

CO3

--H+

H+

Carbonic acidCarbonic acid

OH-WaterWaterH+

CO2 +

Alkalinity & BicarbonatesAlkalinity & Bicarbonates

Neutralization of bicarbonates WILL prevent high pH-related

problems!

Neutralization of bicarbonates WILL prevent high pH-related

problems!

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60 70 80 90

Water

pH

Grower A pH = 9.3 alkalinity = 1.42 meq/L

Grower B pH = 8.3 alkalinity = 6.20 meq/L

Fluid ounces of 35% sulfuric acid/1000 gallons

pH 5.8

Grower B needed more than 4 times the acid to reach a

pH of 5.8 than Grower A

Acidification ProceduresAcidification Procedures➲ Citric, nitric, phosphoric, and

sulfuric acids can be used➲ Citric, nitric, phosphoric, and

sulfuric acids can be used➲ Select an acid based on:➲ Select an acid based on:

• cost• cost

• availability• availability

• handling• handling

• ion being injected (N, P, S)

• ion being injected (N, P, S)

Acid CalculationsAcid Calculations

➲ Developed an acidification

calculator for precise control➲ Developed an acidification

calculator for precise control

➲ Excel 5.0 spreadsheet➲ Excel 5.0 spreadsheet

➲ Download a copy FREE from:

www2.ncsu.edu/floriculture/➲ Download a copy FREE from:

www2.ncsu.edu/floriculture/

➲ Check for $10 to N.C. Ag.

Foundation➲ Check for $10 to N.C. Ag.

Foundation

Version 3.09 / 6 / 9 5

PURDUE UNIVERSITY/NORTH CAROLINA STATE UNIVERSITY GREENHOUSE MEDIA LAB ACID ADDITION CALCULATOR

Name: Joe E. Grower Laboratory ID #: 1000Street: 101 Begonia Lane Client ID of sample: Bad Water

City/State/Zip: Big Bucks, AL 35960 Date: 22-Sep-95

Phone Number: (205) 927-0000FAX Number: (205) 927-1111

This spreadsheet provides the recommendations for the amount of acid to add to irrigation water in order to modify the pH and alkalinity levels. In addition, the spreadsheet calculates the amount of added phosphorus

and nitrogen that the corresponding acids will provide, plus an ecomonic comparison of each acid.

Your Sample InformationThe pH of your sample: 7.4

The alkalinity of your sample: 5.4

Target alkalinity or pH : 5.8(pH must be below 7.2)

Calculated information for your sampleAlkalinity before acid addition meq: 5.40

ppm of HCO3: 329.5ppm of CaCO3: 270.2

Alkalinity after acid additionmeq: 1.27

pH = 5.80 ppm of HCO3: 77.5ppm of CaCO3: 63.6

NC State University / Purdue University Acidification Calculator

Can enter as meq alkalinity, ppm HCO3

-, or ppm CaCO3

Alternative Acids to Add to Irrigation WaterAcids Phosphoric Phosphoric Sulfuric Sulfuric Nitric Nitric

Amounts Acid (75%) Acid (85%) Acid (35%) Acid (93%) Acid (61.4%) Acid (67%)For Small Volumesml per liter 0.335 0.275 0.460 0.115 0.309 0.277

fl. oz. per gallon 0.043 0.035 0.059 0.015 0.040 0.036

ml per gallon 1.267 1.039 1.743 0.437 1.171 1.050

For a 1:100 Injectorfl. oz. per gallon (conc.) 4.28 3.51 5.89 1.48 3.96 3.55

ml per gallon (conc.) 126.65 103.93 174.28 43.68 117.08 105.00





Nutrients Added by Each Type of AcidNutrients Added: Phosphorus Phosphorus Sulfur Sulfur Nitrogen Nitrogen

Amount Added (ppm): 125.3 125.3 66.7 66.7 57.8 57.8

Use the information above for modifying your fertility program.

Cost Comparison of Each Acid Type.(Average prices given here are based on bulk purchases of 5 to 15 gallons.)Date prices were last modified: 1 / 1 0 / 9 5

Acid Treatment Cost* per 1000 Acid Percent Price/Gallon Gallons Liters

Nitric 61.4 $4.00 $1.24 $0.336 7 $5.00 $1.39 $0.37

Phosphoric 7 5 $7.00 $2.34 $0.628 5 $8.00 $2.20 $0.58

Sulfuric 3 5 $1.90 $0.87 $0.239 3 $12.00 $1.38 $0.37

* Reflects only treatment costs and does not include cost savings due to decreased fertilizer needs associated with phosphoric and nitric acids.

Acidification CalculatorAcidification CalculatorAvailable on the Web:Available on the Web:

http://www2.ncsu.edu/floriculture/http://www2.ncsu.edu/floriculture/

Fertilizer Acidity/BasicityFertilizer Acidity/BasicityFertilizer salts alter substrate pHFertilizer salts alter substrate pH

➲ pH changes as plant roots absorb essential elements

➲ pH changes as plant roots absorb essential elements

➲ Nitrate-N (NO3-) raises pH➲ Nitrate-N (NO3-) raises pH

➲ Ammonium-N (NH4+) lowers pH➲ Ammonium-N (NH4+) lowers pH

➲ Other elements also affect pH changes (ex: Ca)

➲ Other elements also affect pH changes (ex: Ca)

Hort Substrates Lab, NCSU

NH4

+

H+

[+] Uptake: pH Falls[+] Uptake: pH Falls

NO3

_

Hort Substrates Lab, NCSU

OH-

[-] Uptake: pH Rises[-] Uptake: pH Rises

4Species

5

6

8

7

pH

Species Effect on pH

Starting pH = 5.9 •Pansy

••••

Tomato

•••••

•• •Begonia

Celosia

Dianthus

•• ••••••••

••Vinca

Zinnia

Marigold (African)

• The same program can result in different pH due to species effect

• Effect is not always good for the plants:

• vinca needs low pH

• celosia and dianthus need high pH

pHpH

8.58.5

8.08.0

7.57.5

7.07.0

6.56.5

6.06.0

5.55.5

5.05.0

4.54.5

TimeTime

pH DriftpH Drift

“optimum” range“optimum” range

Alkaline waterAlkaline water

NH4+ fertilizersNH

4+ fertilizers

Nutritional MonitoringNutritional MonitoringVisual monitoring may be too late...Visual monitoring may be too late...

Need to monitor:pH

Need to monitor:pHECECNutrientsNutrientsTissue analysisTissue analysis

ManagementManagement

We manage what we measure!

We manage what we measure!

MonitoringMonitoring

➲ < 25% of all growers monitor pH and EC on a regular basis

➲ < 25% of all growers monitor pH and EC on a regular basis

➲ Better monitoring = better control

➲ Better monitoring = better control

Substrate pH RegulationSubstrate pH Regulation➲ Monitor pH and EC

regularly and keep

records

➲ Monitor pH and EC regularly and keep records

➲ Maintain the proper pH

and EC for best nutrient

status

➲ Maintain the proper pH and EC for best nutrient status

M&M’s

M & M’sM & M’s

➲ Simple technique for measuring pH and EC

➲ Simple technique for measuring pH and EC

➲ Charts for plotting pH & EC➲ Charts for plotting pH & EC

➲ Recommended ranges for crops

➲ Recommended ranges for crops

M&M’sM&M’sMeasuring TechniqueMeasuring Technique

➲ PourThru➲ PourThru➲ Modification of VTEM➲ Modification of VTEM➲ Simple - fast➲ Simple - fast➲ Non-destructive➲ Non-destructive➲ Values closer to SME

than 2:1➲ Values closer to SME

than 2:1

PourthruPourthruIrrigate your crop one hour before testingIrrigate your crop one hour before testing

PourThruPourThru Place saucer under potPlace saucer under pot

PourThruPourThru Pour distilled water on surfacePour distilled water on surface

PourThruPourThru Collect leachateCollect leachate

PourThruPourThru Use 50 ml of leachateUse 50 ml of leachate

pH RangespH Ranges

General cropsGeneral crops 5.4 to 6.85.4 to 6.8Low pH cropsLow pH crops 5.4 to 5.85.4 to 5.8High pH cropsHigh pH crops 6.0 to 6.86.0 to 6.8

EC RangesEC Rangesmmhos/cmmmhos/cm

LowLow < 1.5< 1.5DesirableDesirable 1.5 to 3.51.5 to 3.5Moderately HighModerately High 3.5 to 5.03.5 to 5.0DangerDanger > 5.0> 5.0

Monitor pHMonitor pH

➲ Measure pH ➲ Measure pH

• Weekly for pots/flats• Weekly for pots/flats

• Every 3 days for plugs• Every 3 days for plugs

➲ Measure species separately, if they require different pH regimes

➲ Measure species separately, if they require different pH regimes

➲ Record data➲ Record data

More InformationMore InformationCheck our Web sites:Check our Web sites:

➲ NCSU Floriculture

• http://www2.ncsu.edu/floriculture/➲ Horticultural Substrates Laboratory

• http://www2.ncsu.edu.hortsublab/

➲ NCSU Floriculture

• http://www2.ncsu.edu/floriculture/➲ Horticultural Substrates Laboratory

• http://www2.ncsu.edu.hortsublab/

M&M

pH M&M’s

“Just Do It…”“Just Do It…”

Monitoring & Maintaining the pH and EC of the Root Environment · 2001-06-27 · Environment...

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