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IRRIGATION WATER QUALITY presented by Burrell Scarlett EVERGROW HORTICULTURAL PRODUCTS
19

Irrigation Water Quality

Aug 18, 2015

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Page 1: Irrigation Water Quality

IRRIGATION WATER QUALITY

presented byBurrell Scarlett

EVERGROW HORTICULTURAL PRODUCTS

Page 2: Irrigation Water Quality

Irrigation Water Quality ManagementFertilizers, Pesticides & Drip Irrigation

Performance

Page 3: Irrigation Water Quality

The efficacy of fertilizers and pesticides are significantly

affected by the quality of the water used to apply these

chemicals. Bad Water Quality, as it relates to Acidity and

Alkalinity can determine how long pesticides remain

effective in solution or whether plant roots will absorb

nutrients. Further, low quality water will quickly block drip

irrigation emitters.

Page 4: Irrigation Water Quality

PESTICIDE USE

Pesticides are normally formulated as weak acids or neutral to

weakly-alkaline products. As a general rule, herbicides,

insecticides, and fungicides perform best in slightly acidic

water, pH 4–6.5. When water pH falls outside of the preferred

upper or lower boundaries, product performance can be

compromised. In some cases, the pesticide can fall out of

solution. The pH of the solution can also influence how long a

pesticide molecule remains effective or be

degraded/hydrolyzed.

Page 5: Irrigation Water Quality

Product Half-Life pH 9 pH 7 pH 5

Herbicides 10 minutes 17 hours 16 days

Fungicides 2 minutes 3 hours 10 hours

Insecticides 24 hours 10 days stable

HALF- LIFE …..(time required for a product to loose 50% of its effectiveness)

Page 6: Irrigation Water Quality

Each pesticide has its specific pH range at which it works best but the following general rules will suffice for most pesticide spray solutions:

• A pH between 3.5 and 6 is satisfactory for most spraying and short-term (12–24 hours)storage of most mixtures in a spray tank. Not suitable for sulfonylurea urea herbicides.

• A pH between 6 and 7 is adequate for immediate spraying for most pesticides. Do not leave the spray mixture in the tank for more than 1–2 hours, to prevent loss of effectiveness.

• Most products mixed in alkaline water should be sprayed immediately.

For more information on Pesticide Breakdown Rates visit: www.nutri-tech.com.au/.../Pesticide%20Breakdown%20Rates.pdf

Page 7: Irrigation Water Quality

BLOCKAGE OF DRIP IRRIGATION EMITTERS

There are three types of clogging hazards that need to be considered in

the design and maintenance of irrigation systems. These are physical,

chemical and biological. All depend on Irrigation Water Quality.

Clearing of chemically blocked drippers may be done by use of acids

or by a bacteria, Agrobacterium FS-16 which dissolves CaCO3

precipitates. The use of acid injection (sulphuric and or phosphoric

acid)or water conditioner to treat chemical deposits (carbonates,

hydroxides and phosphates) in drip irrigation systems is common

amongst growers.

Page 8: Irrigation Water Quality

Since the solubility of Calcium carbonate is reduced as water

temperature increases….do early morning treatments Set pH of

cleaning water solution to 4 for 60 minutes or 2 for 15minutes

in the drip lines.

Flush with pure water after this treatment.

Calcium carbonate is the main chemical deposit which blocks

drip irrigation emitters.

Page 9: Irrigation Water Quality

FERTILIZER USE

Plant roots will not absorb fertilizers efficiently if the pH range is

not optimized i.e. soil and irrigation water pH affect the

availability of all mineral nutrients. Figure 1 below shows that the

absorption of all essential nutrient elements is optimized at pH 5.5

- 6.5. The feeding of specific elements as supplements should be

done within their specified range as indicated below. Example,

Molybdenum is best applied within an alkaline solution of pH

greater than 7, whereas Manganese is best applied in an acidic

solution of pH less than 5.5.

Page 10: Irrigation Water Quality

Figure 1: Influence of nutrients uptake by pH

Page 11: Irrigation Water Quality

Fertilizer Use Efficiency

NUTRIENTSFertilizer Use Efficiency (%)

Soil application Fertigation*

N  30-50 95

P 20 45

K 50 80

* 95% applied fertilizers taken by plants

Page 12: Irrigation Water Quality

FIXING OF PHOSPHATE FERTILIZERS(precipitates)

Acid soils 8 Fe and Al phosphates

FePO4l2H2O, AlPO4

l2H2O

Alkaline soils

4 Ca and Mg phosphates

Page 13: Irrigation Water Quality

Nomenclature

H3PO4 = phosphoric acid

H2PO4- = monobasic

HPO4-2 = dibasic

PO4-3 = tribasic

Page 14: Irrigation Water Quality

Inorganic P Compounds

â Ca(H2PO4)2 â monocalcium phosphate

â CaHPO4

â dicalcium phosphate

â Ca3(PO4)2

â tricalcium phosphate

â 3Ca3(PO4)2lCa(OH)2

â hydroxyapatite

â 3Ca3(PO4)2lCaCO3

â carbonate apatite

decreasing solubility

pH

6

8

Page 15: Irrigation Water Quality

Phosphate Reactions at High pH Values

* P converts to less soluble Ca and Mg compounds

Ca(H2PO4)2 + CaCO3 + H2O ® 2 CaHPO4·2H2O + CO2 very less

soluble soluble

6 CaHPO4·2H2O + 3 CaCO3 ® 3 Ca3(PO4)2 + 3 CO2 + 5 H2O

less soluble

3 Ca3(PO4)2 + CaCO3 ® 3Ca3(PO4)2·CaCO3

very insoluble

- most serious in calcareous soils of arid regions

Page 16: Irrigation Water Quality

PHOSPHATE FERTILIZERSPO3−

4    HPO2−4   H2PO−

4

In  dilute aqueous solution, phosphate exists in four forms.

For Solubility:(H3PO4) H2PO−4>HPO2−

4>PO3−4

 (H2PO4)− is most common , and most soluble at about pH 5.5

(H2PO4)− is mostly available as, Mono-Ammonium Phosphate, MAP

or Mono-Potassium Phosphate, MKP and used extensively in fertigation.

In soil cropping, the compound superphosphate,  Ca(H2PO4)2 is a very

common fertilizer producing phosphorus to the plant.

Ca3(PO4)2 + 2H2SO4 = Ca(H2PO4)2 + 2CaSO4

Page 17: Irrigation Water Quality

In summary, to optimize the use of phosphate fertilizers, the grower must manage irrigation water pH.

Page 18: Irrigation Water Quality

Phosphate Ion: Protonation

acid soils alkaline soils

Page 19: Irrigation Water Quality

CORRECTING THE pHIrrigation water and water used for mixing pesticides are usually

alkaline and therefore not suitable for direct use. Acid based

compounds called water conditioners or acidifiers are usually

used to lower the pH. A bacteria, Agrobacterium FS-16 is also

able to dissolve CaCO3 precipitates.

•EVERGROW WATER CONDITIONER reduces the pH of the

water to proper levels suitable for pesticide and fertilizer

solutions.