Fertilizer is an important component of any operation. However, rising raw material costs have put all crop inputs under close scrutiny. Fertigation systems boost fertilizer use efficiency, allowing growers to tailor fertilizer applications to both crop growth and the environment. However, there are still areas where small economies can be made, helping to increase the dollar return on the fertilizer investment.

For larger operations, solid fertilizer sources are a less expensive alternative to the commonly used liquid formulations. The solubility of these fertilizers does vary greatly. When switching to a solid fertilizer source, avoid problems in the nurse tanks by ensuring that ample water is added to the stock solution.

Urea Ammonium Nitrate (UAN) is often considerably less expensive than Calcium Ammonium Nitrate. It also contains more nitrogen on a per volume basis (28% vs. 17%) allowing for lower application rates.

Regardless of the fertilizer source, rate selection and dilution is critical. To avoid fertilizer injury, aim for a fertilizer concentration of 1-2% of the total water volume. Do not exceed concentrations of more than 5%.

Plan to inject the fertilizer over 1-2 hours at the end of the irrigation cycle. Studies have shown that fertigating at the beginning of the cycle may cause the fertilizer to move below the crop's rooting zone where it is less available for crop uptake. Be sure to run the system long enough to properly flush the fertilizer from the drip lines after the injection period.

Always check for fertilizer compatibility. DO NOT mix fertilizer solutions containing calcium with solutions containing phosphates or sulphates. Table below outlines the compatibilities of the most common fertilizer sources. When using a new fertilizer source, do a jar test to ensure there are no incompatibilities. Mix the fertilizer solutions with a sample of the irrigation water and allow it to sit for 1-2 hours. If the products are incompatible, precipitates will form or the sample will become cloudy.

Fertigation Fertilizer Compatibility Chart
Urea, Ammonium Nitrate, Ammonium Sulphate, CN, PN, Potassium Chloride, SOP, Ammonium Phosphate, Fe/Zn/Cu/Mn Sulphate, Fe/Zn/Cu/Mn Chelate, Mag Sulphate, Phosphoric Acid, Sulphuric Acid, Nitric Acid

Urea => Urea
Ammonium Nitrate => Urea, Ammonium Nitrate
Ammonium Sulphate => Urea, Ammonium Nitrate, Ammonium Sulphate
Calcium Nitrate => Urea, Ammonium Nitrate; x = Ammonium Sulphate
Potassium Nitrate => Urea, Ammonium Nitrate, Ammonium Sulphate, CN
Potassium Chloride => Urea, Ammonium Nitrate, Ammonium Sulphate, CN, PN
Potassium Sulphate @ SOP => Urea, Ammonium Nitrate, PN; R= Ammonium Sulphate, Potassium Chloride; x = CN;
Ammonium Phosphate =>Urea, Ammonium Nitrate, Ammonium Sulphate, PN, Potassium Chloride, SOP Ammonium Phosphate; x = CN;
Fe/ Zn/ Cu/ Mn Sulphate =>Urea, Ammonium Nitrate, Ammonium Sulphate, PN, Potassium Chloride; R = SOP; x = CN, Ammonium Phosphate
Fe/ Zn/ Cu/ Mn Chelate => Urea, Ammonium Nitrate, Ammonium Sulphate, PN, Potassium Chloride, SOP; R = CN, Ammonium Phosphate;
Magnesium Sulphate (MgS) => Urea, Ammonium Nitrate, Ammonium Sulphate,PN, Potassium Chloride,Fe/Zn/Cu/Mn Sulphate, Fe/Zn/Cu/Mn Chelate; R = SOP; x = CN, Ammonium Phosphate
Phosphoric Acid => Urea, Ammonium Nitrate, Ammonium Sulphate, PN, Potassium Chloride, SOP, Ammonium Phosphate, Fe/Zn/Cu/Mn Sulphate, Magnesium Sulphate, R = Fe/Zn/Cu/Mn Chelate, x = CN
Sulphuric Acid => Urea, Ammonium Nitrate, Ammonium Sulphate,PN, Potassium Chloride,SOP, Ammonium Phosphate, Fe/Zn/Cu/Mn Sulphate, Fe/Zn/Cu/Mn Chelate, Mag Sulphate, Phosphoric Acid , R = SOP; x = CN
Nitric Acid => Urea, Ammonium Nitrate, Ammonium Sulphate, CN, PN, Potassium Chloride, SOP, Ammonium Phosphate, Fe/Zn/Cu/Mn Sulphate, Mag Sulphate, Phosphoric Acid, Sulphuric Acid, x = Fe/Zn/Cu/Mn Chelate

PN = Potassium Nitrate
CN = Calcium Nitrate
SOP = Potassium Sulfate @ Sulfate of Potash
Legend:
=> compatible; x = incompatible; R = reduced compatibility