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
For a 1:128 Injectorfl. oz. per gallon (conc.) 5.48 4.50 7.54 1.89 5.07 4.54
ml per gallon (conc.) 162.12 133.03 223.08 55.91 149.86 134.39
For a 1:200 Injectorfl. oz. per gallon (conc.) 8.57 7.03 11.79 2.95 7.92 7.10
ml per gallon (conc.) 253.31 207.85 348.56 87.37 234.16 209.99
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…”
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