irrigation water quality
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- 1. presented by Burrell Scarlett EVERGROW HORTICULTURAL PRODUCTS
- 2. Irrigation Water Quality Management Fertilizers, Pesticides & Drip Irrigation Performance
- 3. 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.
- 4. 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 46.5. 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.
- 5. 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)
- 6. 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 (1224 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 12 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
- 7. 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.
- 8. 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.
- 9. 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.
- 10. Figure 1: Influence of nutrients uptake by pH
- 11. Fertilizer Use Efficiency NUTRIENTS Fertilizer Use Efficiency (%) Soil application Fertigation* N 30-50 95 P 20 45 K 50 80 * 95% applied fertilizers taken by plants
- 12. FIXING OF PHOSPHATE FERTILIZERS (precipitates) Acid soils 8 Fe and Al phosphates FePO4 l2H2O, AlPO4 l2H2O Alkaline soils 4 Ca and Mg phosphates
- 13. Nomenclature H3PO4 = phosphoric acid H2PO4 - = monobasic HPO4 -2 = dibasic PO4 -3 = tribasic
- 14. Inorganic P Compounds Ca(H2PO4)2 monocalcium phosphate CaHPO4 dicalcium phosphate Ca3(PO4)2 tricalcium phosphate 3Ca3(PO4)2 lCa(OH)2 hydroxyapatite 3Ca3(PO4)2 lCaCO3 carbonate apatite decreasing solubility pH 6 8
- 15. 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
- 16. PHOSPHATE FERTILIZERS PO3 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
- 17. In summary, to optimize the use of phosphate fertilizers, the grower must manage irrigation water pH.
- 18. Phosphate Ion: Protonation acid soils alkaline soils
- 19. CORRECTING THE pH Irrigation 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.
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