Water Quality And Greenhouse Crops Bodie Pennisi University of Georgia

Why Need To Know Water Quality ? Irrigation water affects pH of the soil solution pH controls nutrient mobility Water quality is NOT static!

 Media pH is affected by:  lime incorporated  water alkalinity and pH  type of fertilizer used (basic or acidic)

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 (CaCO 3, more reactive) or dolomitic (CaMgCO 3 )  particle size: the finer the more reactive  hardness: agricultural limestone is soft and reactive, building limestone is non-reactive

The Goal Is To Achieve A Stable Medium pH Over Time

Alkalinity Terms Milliequivalents alkalinity mg/liter or ppm CaCO 3 of alkalinity mg/liter or ppm bicarbonate

Sample A Sample B pH = 9 pH = 7 One drop of acid to get pH 6 Ten drops of acid to get pH 6 The Effect of Water Alkalinity on Media pH and Acid Requirement Little or no effect on the growing medium pH Increases growing medium pH Alk = 50 ppm Alk = 300 ppm

 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 pHpH

CaMg(CO 3 ) 2 Dolomitic limestone Ca 2+ + Mg CO 3 2- Hardness Alkalinity 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

 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 CaCl 2 and/or MgCl 2 HardnessHardness

 If you have hard water:  check Ca and Mg concentrations  if high use less lime  monitor pH !  check Ca : Mg ratio  ideal ratio is 3:1 if expressed in meq/L  ideal ratio is 5:1 if expressed in ppm HardnessHardness

H 2 CO 3 2CO H + H 2 O + CO 2 Substrate Acidity Alkalinity Both the alkalinity and the acidity are neutralized

 What is “best” alkalinity level ? (One that maintains stable media-pH over time) (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 AlkalinityAlkalinity

Poinsettia Crop 10 Weeks After Planting (adopted from Greenhouse Grower, January 2001, p.72) Leaching Fraction Media pH The more water applied to the crop, the greater effect high alkalinity water will have on media pH. Initial media pH = 6.0 Water alkalinity = 320 ppm CaCO 3

Alkalinity Guidelines Pot Diameter/Size Impacts the Effect of Alkalinity (From Scotts Testing Lab) Alkalinity Guidelines Pot Diameter/Size Impacts the Effect of Alkalinity (From Scotts Testing Lab) Container Size Optimum Range ppm CaCO 3 Level of Concern* Plugs Small pots/ shallow flats 4”-5” pots/deep flats 6” or larger pots/long term crops * The highest level that a grower can manage depends on the plant species, media type, potential acidity of feed program and watering practices

Fertilizers and Water

 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. It Is Important To Remember:

Weeks from Planting Root Media pH The same fertilizer 97% nitrate nitrogen at 200 ppm N was applied (adopted from Greenhouse Grower, January 2001, p.72) Effect of Water Alkalinity on Media pH Over Time

Weeks from Planting Root Media pH (adopted from Greenhouse Grower, February 2001, p.68) Stable Media pH Can Be Obtained By Number of Different Ways by Manipulating Both the NH 4 -N to NO 3 N Ratio and Water Alkalinity

Weeks from Planting Root Media pH (adopted from Greenhouse Grower, February 2001, p.72) Residual Lime’s 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 The same acidic fertilizer (50% ammonical N at 200 ppm with water alkalinity of 200 ppm CaCO 3 ) was used

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 ) CaCO 3 Equivalency (lbs/ton) % Acidic Nitrogen = (ammonium + urea)/ total N > 500 acidic > 50% acidic 150 acidic to 150 basic > 150 basic 20-30% 40% <15% Examples Alkalinity concentration (ppm CaCO 3 ) that provides a stable media pH

Dealing With High And Low Water Alkalinity

Action Steps To Correct High Alkalinity reverse osmosis acid injection acid fertilizer and/or none less lime Alkalinity (ppm) bicarbonate

 If acid injection required, use the Alkalinity Calculator found on: oftware/ 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. 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 about 80 ppm; pH of 6.2 – about 120 ppm.  Needs to measure alkalinity with a test kit in- house or a lab test. Correcting High 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 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. Low Alkalinity

 Research showed that rates of 4 lbs/100 gal KHCO 3 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 KHCO 3 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 or ) to remove high levels of potassium and restore nutrient balance. Tips for Using Flowable Lime or Potassium Bicarbonate (KHCO 3 )

 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.

Other Factors

SalinitySalinity  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

SalinitySalinity  Sodium – high sodium can interfere with Mg 2+ and Ca 2+ 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

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.

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: 1. STABILIZATION (Precipitation Inhibitors) Stabilization treatments keep the ferrous iron in solution by chelating it with sequestering agents. Such agents include various poly phosphates and phosphonate. 2. 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.

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.

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.

MicronutrientsMicronutrients  Chlorine – commonly associated with sodium (NaCl); problem if > 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 > than 0.5 ppm.

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

Where Does The Water Come From ?

Frequency % Irrigation Water Alkalinity concentrations (ppm CaCO 3 ) from Florida <40 40– >400

Testing The Waters …

Testing Water Quality In-House  Range 0-8 meq/L (0-400 ppm alkalinity expressed as CaCO 3 )  Accuracy  0.4 meq/L or better  Kits from $30 for 100 tests to $155 for 100 tests. $155 for 100 tests.

Water Quality Kit

Commercial Lab

1.Need test for alkalinity 2.Need Fluorine (F) and/or Chlorine (Cl) if high levels are suspected.

How Often Should Water Quality Be Checked?

Soil Zone Sand and Gravel Aquifer Limestone or Granite Aquifer Sandstone Aquifer Examples of Variation in Groundwater Quality Well # 1Well # 2Well # 3

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.

The Plan From Now On … The

Pre-test irrigation water and media before planting. Pre-test irrigation water and media before planting. Stock up on pH-adjusting chemicals and basic fertilizers. 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. 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. Set up a pH, EC and nutrient monitoring program.