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Where Does The Water Come From ?. Examples of Variation in Groundwater Quality. Well # 1. Well # 2. Well # 3. Soil Zone. Sand and Gravel Aquifer. Limestone or Granite Aquifer. Sandstone Aquifer. Irrigation Water Alkalinity concentrations (ppm CaCO 3 ) from Florida. 25 20 15

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Where Does The Water Come From ?

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Where Does The Water Come From ?


Examples of Variation in Groundwater Quality

Well # 1

Well # 2

Well # 3

Soil Zone

Sand and Gravel Aquifer

Limestone or Granite Aquifer

Sandstone Aquifer


Irrigation Water Alkalinity concentrations (ppm CaCO3) from Florida

25

20

15

10

5

0

Frequency %

<40

40–80

80-20

120-160

160-200

200-240

240-280

280-320

320-360

360-400

>400


The Goal Is To Achieve A Stable Medium pH Over Time


Plant Growth Cycle

Active Growth

Establishment

Mature


pH

  • pH affects the solubility of fertilizers, and the efficacy of pesticides and growth regulators.

    • the higher the water pH the less soluble these materials are


pH Drift

8.5

8.0

7.5

7.0

6.5

6.0

5.5

5.0

4.5

Alkaline Water

pH

“Optimum” Range

NH4+ fertilizers

Time


Alkalinity

  • A measure of water’s ability to neutralize acids – a buffering ability

  • Mostly carbonates and bicarbonates – associated with Ca and Mg (limestone)

  • May cause pH to rise in media over time, especially in small containers

Note: Alkalinity “controls” pH

Must know alkalinity to manage pH


Alkalinity

  • Expressed in ppm, mg/L, meq/L

  • Expressed as CaCO3 or HCO3-

  • Irrigation water should have an alkalinity of less than 100ppm; if higher than 150 ppm, acidification is needed


Alkalinity

CaMg(CO3)2

Ca2+ + Mg2+ + 2CO32-

Dolomitic limestone

Hardness

Hardness and Alkalinity Generally Go Hand-In-Hand but They Are NOT One and the Same

You Can Use the Water Hardness to Estimate Its Alkalinity


Alkalinity Terms

mg/liter or ppm CaCO3 of alkalinity

mg/liter or ppm bicarbonate

Milliequivalents alkalinity

1

2

3

4

5

50

100

150

200

250

60

122

183

244

305


Substrate Acidity

2CO32- + 2H +

H2CO3

Alkalinity

H2O + CO2

Both the alkalinity and the acidity are neutralized


The Effect of Water Alkalinity on Media pH and Acid Requirement

Sample A

Sample B

pH = 9

pH = 7

Alk = 50 ppm

Alk = 300 ppm

Increases growing medium pH

Little or no effect on the growing medium pH

One drop of acid to get pH 6

Ten drops of acid to get pH 6


Action Steps To Correct High Alkalinity

reverse osmosis

480

Alkalinity (ppm) bicarbonate

acid injection

180

120

acid fertilizer and/or

less lime

none


SalinitySalinity is measured by Electro-conductivity

  • Total Dissolved Salts (TDS) – all salts present in the water (1 mMho/cm=640 ppm)

    • less than 0.75 mMho /cm for plugs

    • less than 1.0 mMho /cm for other greenhouse crops

    • less than 2.0 mMho /cm for other nursery crops


Testing The Soil Solution !


Pour Thru Method

  • Simple technique for measuring pH and EC

  • Charts for recording pH & EC

  • Guidelines for crops

  • Procedures to keep on track


6 or 8-inch saucers are adequate for collecting the leachate


Distilled Water Volumes

Pot Size

ml

oz

4 inch

5 inch

6 inch

6.5 inch

1 Qt

4 Qt

12 Qt

75

75

75

100

75

150

350

2.5

2.5

2.5

3.5

2.5

5.0

12.0


Flats: Use 50 ml Distilled Water


EC Comparisons

1:2

SME

Indication

PourThru

0 to 0.3

0.3 to 0.8

0.8 to 1.3

1.3 to 1.8

1.8 to 2.3

> 2.3

0 to 0.8

0.8 to 2.0

2.0 to 3.5

3.5 to 5.0

5.0 to 6.0

> 6.0

0 to 1.0

1.0 to 2.6

2.6 to 4.6

4.6 to 6.5

6.6 to 7.8

> 7.8

Very Low

Low

Normal

High

Very High

Extreme


Initial EC


Crop pH Ranges


Geraniums (6” pinched)

6.0 to 6.6

1/28

6.6 to 6.8

5/01

5.8 to 6.0


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