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Water Quality

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the higher the water pH the less soluble these materials are Hardness Hardness Alkalinity Fertilizers and Water Dealing With High And Low Water Alkalinity Action ... – PowerPoint PPT presentation

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Title: Water Quality


1
Water Quality And Greenhouse Crops
Bodie Pennisi University of Georgia
2
Why Need To Know Water Quality ?
Irrigation water affects pH of the soil
solution pH controls nutrient mobility
Water quality is NOT static!
3
  • Media pH is affected by
  • lime incorporated
  • water alkalinity and pH
  • type of fertilizer used (basic or acidic)

4
Factors that Affect Medium pH
  • Buffering capacity of the medium.
  • peat, bark, coir, perlite, vermiculite
  • indirectly - how much lime is incorporated?
  • directly type and rate of lime
  • type of limestone calcitic (CaCO3, more
    reactive) or dolomitic (CaMgCO3)
  • particle size the finer the more reactive
  • hardness agricultural limestone is soft and
    reactive, building limestone is non-reactive

5
The Goal Is To Achieve A Stable Medium pH
Over Time
6
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
7
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
8
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

9
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
10
Hardness
  • Calcium and magnesium are the major
    contributors
  • hard water has a high Ca and/or Mg
  • hard water is generally associated with high
    alkalinity
  • can have hard water and low alkalinity water
    high in CaCl2 and/or MgCl2

11
Hardness
  • If you have hard water
  • check Ca and Mg concentrations
  • if high use less lime
  • monitor pH !
  • check Ca Mg ratio
  • ideal ratio is 31 if expressed in meq/L
  • ideal ratio is 51 if expressed in ppm

12
Substrate Acidity
H2CO3
2CO32- 2H
Alkalinity
H2O CO2
Both the alkalinity and the acidity are
neutralized
13
Alkalinity
  • What is best alkalinity level ?
  • (One that maintains stable media-pH over
    time)
  • Research says anywhere between
    40 and 120 ppm bicarbonate
  • However, there is probably not ONE best
    alkalinity level ! Depends on
  • the length of the crop cycle
  • the plant to substrate ratio
  • upper substrate pH that the crop can tolerate

14
Poinsettia Crop 10 Weeks After Planting (adopted
from Greenhouse Grower, January 2001, p.72)
Initial media pH 6.0 Water alkalinity 320 ppm
CaCO3
Media pH
Leaching Fraction
The more water applied to the crop, the greater
effect high alkalinity water will have on media
pH.
15
Alkalinity Guidelines Pot Diameter/Size Impacts
the Effect of Alkalinity (From Scotts Testing Lab)
Optimum Range ppm CaCO3
Level of Concern
Container Size
60 - 100
lt 40, gt 120
Plugs
Small pots/ shallow flats
lt 40, gt 140
80 - 120
100 - 140
lt 40, gt 160
4-5 pots/deep flats
6 or larger pots/long term crops
120 - 180
lt 60, gt 200
The highest level that a grower can manage
depends on the plant species, media type,
potential acidity of feed program and watering
practices.
16
Fertilizers and Water
17
It Is Important To Remember
  • the fertilizer solution you apply to the crop is
    made up of irrigation water and water-soluble
    fertilizer
  • it is the combination of the alkalinity in the
    irrigation water and the reaction of the
    water-soluble fertilizer that affects media pH
  • the balance between the ammonical nitrogen in
    the fertilizer and water alkalinity has the
    greatest effect on media pH over time.

18
(adopted from Greenhouse Grower, January 2001,
p.72)
Effect of Water Alkalinity on Media pH Over Time
The same fertilizer 97 nitrate nitrogen at 200
ppm N was applied
Root Media pH
Weeks from Planting
19
(adopted from Greenhouse Grower, February 2001,
p.68)
Stable Media pH Can Be Obtained By Number of
Different Ways by Manipulating Both the NH4-N to
NO3 N Ratio and Water Alkalinity
Root Media pH
Weeks from Planting
20
(adopted from Greenhouse Grower, February 2001,
p.72)
Residual Limes Effects
Media 1 contained hydrated lime (leaves no
residual lime in the media) Media 2 contained
same peat as 1 but a dolomite was used (large
residual) Media 3 contained the same rate of
dolomite as 2 but used a different peat with
higher lime requirement
Root Media pH
The same acidic fertilizer (50 ammonical N at
200 ppm with water alkalinity of 200 ppm CaCO3)
was used
Weeks from Planting
21
Approximate Guidelines to Matching Fertilizers
with Water Alkalinity in Order to Achieve a
Stable pH Over Time. Use these values as a
starting point only. It is up to the grower to
make changes in media pH that are based on actual
pH measurements in the crop. (adopted from
Greenhouse Grower, February 2001, p.62)
Alkalinity concentration (ppm CaCO3) that
provides a stable media pH
CaCO3 Equivalency (lbs/ton)
Acidic Nitrogen (ammonium urea)/ total N
Examples
20-20-20 25-10-10
gt 500 acidic
200-300
gt 50
20-10-20 21-5-20
150-500 acidic
150-250
40
150 acidic to 150 basic
20-0-20 17-5-17
60-120
20-30
gt 150 basic
13-2-13 14-0-14
lt15
30-60
22
Dealing With High And Low Water Alkalinity
23
Action Steps To Correct High Alkalinity
reverse osmosis
480
Alkalinity (ppm) bicarbonate
acid injection
180 120
acid fertilizer and/or
less lime
none
24
Correcting High Alkalinity
  • If acid injection required, use the Alkalinity
    Calculator found on
  • www.ces.ncsu.edu/depts/hort/floriculture/software/

25
Correcting High Alkalinity
  • Most commonly used acids sulfuric, phosphoric,
    nitric.
  • Need to consider the extra phosphorus (P),
    nitrogen (N), or sulfur (S) in the acid when
    selecting fertilizer.
  • 3.4 fl oz of 85 phosphoric acid/100 gal adds
    122 ppm P to the irrigation water
  • If acid is changed, nutritional program needs to
    be re-evaluated.

26
Correcting High Alkalinity
  • With some injectors may be difficult to figure
    out how much acid is being added. The solution pH
    can give a rough estimate of how much alkalinity
    is left
  • a solution pH of 5.2 will have about 40 ppm
    alkalinity pH of 5.8 - about 80 ppm
    pH of 6.2 about 120 ppm.
  • Needs to measure alkalinity with a test kit
    in-house or a lab test.

27
Low Alkalinity
  • Low alkalinity is not desirable.
  • the buffering capacity of the irrigation
    solution is low
  • if using acidic fertilizers it can lead to low
    substrate pH and increased micronutrient levels
  • using nitrate fertilizers will raise the media
    pH and keep it at a constant level and not cause
    it increase

28
Low Alkalinity
  • If alkalinity is less than 40 ppm, you may
    consider
  • increasing the lime in the media
  • using basic (nitrate-based) fertilizer
  • If pH falls below 5.8 for sensitive crops
  • apply flowable lime or potassium bicarbonate and
    check pH after 3 days
  • re-apply again if pH remains below 6.0 after 3
    days.

29
Tips for Using Flowable Lime or Potassium
Bicarbonate (KHCO3)
  • Research showed that rates of 4 lbs/100 gal
    KHCO3 or 4 qts/100 gal flowable lime can cause
    phytotoxicity to roots or foliage if solution is
    not immediately rinsed off foliage.
  • recommended rates are 2 lbs/100 gal KHCO3 or
    4 qts/100 gal flowable lime
  • If applying potassium bicarbonate follow the day
    after with heavy leaching with basic fertilizer
    that contains Ca and Mg (such as 13-2-13 or
    14-0-14) to remove high levels of potassium and
    restore nutrient balance.

30
Tips for Using Flowable Lime or Potassium
Bicarbonate (KHCO3)
  • Do not apply to dry soil. Media should rewet and
    absorb the chemical easily.
  • Apply sufficient volume to achieve at least 30
    leaching.
  • Apply in cool part of the day so that lime does
    not dry quickly on foliage and can be easily
    washed off.
  • Immediately rinse foliage before chemical dries
    using clear water in a back-pack sprayer.

31
Other Factors
32
Salinity
  • Total Dissolved Salts (TDS) all salts
    present in the water (1 mMho/cm640 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

33
Salinity
  • Sodium high sodium can interfere with Mg2
    and Ca2 availability, and cause foliar burns
    associated with poor water uptake and sodium
    accumulation in the tissues.
  • Sodium Adsorption Ratio (SAR)
  • problem if higher than 4 meq/L

34
Iron and Iron-Fixing Bacteria
  • Excess iron and iron bacteria can cause
    unsightly brown stains or bluish sheen on foliage
    and flowers.
  • As little as 0.3 ppm iron in the water could
    lead to deposits if overhead irrigation is used
    and the sheen can cause clogging in drip systems.
  • Iron problems can come from two sources well
    water that contains iron, and iron-fixing
    bacteria in water storage basins.

35
  • IRON CONTROL METHODS
  • There are several ways to control iron slime
    problems.
  • The common denominator of all treatments is
    prevention of the formation of slime. Basically
    there are two preventive treatments
  • STABILIZATION (Precipitation Inhibitors) Stabiliz
    ation treatments keep the ferrous iron in
    solution by chelating it with sequestering
    agents. Such agents include various poly
    phosphates and phosphonate.
  • OXIDATION - SEDIMENTATION - FILTRATION This
    type of treatment oxidizes the soluble
    "invisible" ferrous iron into the insoluble
    "visible" ferric iron. It then will precipitate,
    so it can be physically separated from the water
    by filtration.

36
Removing Iron and Iron-Fixing Bacteria
  • Aerate irrigation water in a holding pond, which
    allows for the iron to precipitate before it
    reaches the plants.
  • If iron-fixing bacteria are present, this
    measure may not be sufficient. Adjust the
    irrigation intake location. The intake should be
    located 18 to 30 below the surface to avoid
    pulling in the oily surface sheen, at least 18
    deep to prevent "vortexing" from the surface, and
    should be up from the bottom to avoid pulling up
    iron sediment.
  • The next step is to install a basin aeration
    pump, which helps precipitate the iron, thus
    reducing the food source for the iron bacteria.

37
Removing Iron and Iron-Fixing Bacteria
  • Inject chlorine in the water in conjunction with
    an irrigation filter. The chlorine must be in
    contact with irrigation water for one minute to
    be effective. To accommodate the chlorine
    injection, the irrigation system needs
    retrofitting, which may require storage tanks,
    swirl chambers or extra loops in the irrigation
    lines.
  • Two forms of chlorine can be used gas or
    liquid. Gas is the most efficient and effective,
    but is also hazardous. Liquid chlorine injection
    is safer. A filtering system that removes
    organic residue will reduce the amount of
    chlorine required. Usually two filters are
    installed, so one can be back flushed and cleaned
    while the other is filtering irrigation water.

38
Micronutrients
  • Chlorine commonly associated with sodium
    (NaCl) problem if gt than 2 meq/L.
  • Fluorine levels above 1 ppm may cause foliar
    problems on sensitive crops such as lilies and
    freesias it can accumulate in the media.
  • Boron high levels are associated with alkaline
    soils in areas of low rainfall
    problem if gt than 0.5 ppm.

39
Managing High Salinity in Water Supply
  • Dilute with collected rainwater or other low
    salinity water sources
  • Use reverse osmosis water treatment,
    particularly for misting cuttings, irrigating
    seedlings, and salt-sensitive crops

40
Where Does The Water Come From ?
41
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45
Irrigation Water Alkalinity concentrations (ppm
CaCO3) from Florida
25 20 15 10 5 0
Frequency
lt40 4080 80-20 120-160 160-200 200-240 240-280 28
0-320 320-360 360-400 gt400
46
Testing The Waters
47
Testing Water Quality In-House
  • Range 0-8 meq/L (0-400 ppm alkalinity expressed
    as CaCO3)
  • Accuracy ? 0.4 meq/L or better
  • Kits from 30 for 100 tests to
  • 155 for 100 tests.

48
Water Quality Kit
49
Commercial Lab
50
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53
  1. Need test for alkalinity
  2. Need Fluorine (F) and/or Chlorine (Cl) if high
    levels are suspected.

54
How Often Should Water Quality Be Checked?
55
Examples of Variation in Groundwater Quality
Well 1
Well 2
Well 3
Soil Zone
Sand and Gravel Aquifer
Limestone or Granite Aquifer
Sandstone Aquifer
56
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57
Water Quality Should Be Checked
  • Every time a new water source is added.
  • Once during a dry season and once during rainy
    season.
  • More frequently with shallow wells.

58
The Plan From Now On
59
Pre-test irrigation water and media before
planting. Stock up on pH-adjusting chemicals and
basic fertilizers. Use a water test analysis to
select the fertilizer and decide whether to
acidify irrigation water. Set up a pH, EC and
nutrient monitoring program.
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