Taking an environmentally sensitive approach to pest management


Missouri Produce Growers


James Quinn
University of Missouri
(573) 634-2824

Irrigation water quality

James Quinn
University of Missouri
(573) 634-2824

Published: August 1, 2010

Growers are encouraged to test their water every couple of years so they can be confident about their water source, and make adjustments if needed. While irrigation water quality is more critical for nursery and greenhouse crops then vegetables, high tunnel production of vegetables could develop problems, especially over time as the soil does not receive rainfall that would leach out accumulating salts or carbonates.

Water from a well source is more likely to have alkalinity, pH or salt problems then surface sources. A significant concern with surface water is contamination from agricultural practices, especially row crop herbicides.

So what parameters do we want from our irrigation source?

  • A pH within 5.5 to 6.5;
  • Alkalinity – less than 400 ppm of CaCO3, the lower the better!
  • Salt - EC below 0.25 is considered excellent; 0.25 to 0.75 is considered good. Irrigation water is permissible all the way up to an EC of 2.0 if precautions are taken. Above 2.0 is doubtful.

Did you realize some pesticides are negatively effected by water that is high in pH? For example, the Round Up Original Max label says with hard water conditions, that the addition of 1 to 2% dry ammonium sulfate may improve the performance on annual and perennial weeds.

A tip from an MU Specialist in SW Missouri, where the water is 'hard', if you don't have any ammonium sulfate, try substituting household vinegar, at these rates:

  • For water with a pH over 7, use one ounce per gallon of mix;
  • For water with a pH less then 7, but over 6.5, use one tablespoon per gallon of mix.

Two teaspoons of Dawn liquid detergent per gallon of mix is an acceptable household substitute for crop oil. Crop oil is advised for some tough to kill weeds, usually those where the leaf surface is difficult to adhere or penetrate.

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REVISED: December 2, 2015