Pasture water quality for cows

Make sure you know your water quality before you turn the cows out

Most of my articles about slough water have dealt with water in the sprayer and what it might do to herbicide results. But bad pasture water that killed 200 cows in southern Saskatchewan last summer has sharpened the focus on water for stock.

Spring is nigh, so cowboys should be sure they know what their cows are going to drink. From my article published in the August 29, 2017 of Grainews, the following info explains how it all works.

Measuring salt content of water

Salt content of water can be very easily measured in the field with sufficient accuracy to be very useful for many problems. Salts carry an electric charge. The more salts in a water the more electric current it will carry. We measure that as the EC (electrical conductivity). The higher the EC the higher the salt content of the water.

EC is reported in microSiemens per centimeter (µS/cm). EC is temperature dependent so all readings are corrected to a standard 25 C. For many of our waters, EC is a good first approximation of the total dissolved solids in parts per million (ppm).

As a first approximation, interpretation of EC (µS/cm) results for cows is:

  • EC < 1,000 µS/cm: Good to go, but water that good is rare in some areas.
  • EC 1,000 to 5,000 µS/cm: Problems increase and there may be poor production even if no actual serious distress.
  • EC > 5,000 µS/cm: You should be looking for a better water source.
  • EC > 10,000 µS/cm: Forget it. Find another source.

A tale of three sloughs

The table below shows data from three sloughs on my home quarter over a period of 11 years. From about 1999 to 2003 those sloughs had very little water. In 2002 there was not a drop of surface water on the quarter; hay was cut in the west slough for a few years around the turn of the century.

*MASL = meters above sea level Photo: File

We normally think that wet cycles will provide fresh water from rain or snowmelt and the water will get better. In dry cycles evaporation will concentrate the salts.

But it is not that simple. In 2002 almost all the sloughs in the hilly land around my farm were dry. We have used long-term water well records to show that from 1975 to 2005 was a 30-year cumulative net water deficit (drought). We still managed some decent crops if timely rains came along, but each year the water tables were dropping. The water pressure in shallow aquifer systems was also dropping.

The 30-year drought was broken by the big snowmelt in spring of 2005. That and subsequent wet years, provided excess water to wash salts out of the soil naturally. As the sloughs filled up, the water quality was good. But as wet years continued ground water systems were juiced up and pressure from beneath began moving subsoil salts to the surface. Also, sloughs with salt rings overflowed the ring and dissolved many more salts. Even though there was more water, it was also more salty.

These cumulative effects over 11 years on my little place have resulted in about a six- to nine-fold increase in salinity in the water.

The 2017 numbers show what can happen in a single season with little rain. The “best” slough (east) had an increase in salinity of 23 per cent from July 26 to October 24. The “worst” slough (west) had an increase of 50 per cent in that same time period.

As of 2017 my west slough has reached a point where it would not be wise to use it for stock and it would really do a number on the efficacy of glyphosate herbicide if used in the spray tank.

A nearby pasture

A nearby pasture with a slough/dugout that caused big problems for stock in 2001 has the following EC numbers:

  • October 2, 2001: 14,750 µS/cm
  • October 10, 2015: 2,050 µS/cm
  • July 26, 2017: 2,890 µS/cm

I did not measure it in October 2017, but in future I will keep an eye on that for the neighbours.

The future

There is no way to know the weather over the next few years but common sense tells me we will be in for the other side of the average before long. If the 2015 and 2017 dry summers are the start of something, then cowboys had better keep a close eye on pasture water supplies.

At least some veterinarians have purchased EC meters and are measuring water for clients. I have been in contact with Tiffany Pomarenski of RY Trails Veterinary Services of Ogema, Sask., and she is learning fast with her EC meter. There is nothing like getting data on the spot to deal with a problem. Many folks may have a problem that is not killing stock but is hampering production.

Measuring EC in the field

Measuring water EC in the field is very easy. The photo shows me measuring water EC in Lac la Ronge off the dock at Harbour View Inn on August 5, 2005. Everything needed to do the job is in that little briefcase, including the notebook to keep the records. The result? EC = 215 uS/cm, less than half that of the South Saskatchewan River at Saskatoon. We did a soils tour through the northeast bush areas that summer and measuring water EC was boring — rivers, lakes, etc., were all about the same (EC = 200).

There is no reason to lose cows to salty water or have a herbicide behave badly because of hard water. Field equipment must be kept “honest” by frequent checks against a known source and submitting some samples to labs. But, in 35 years of measuring water EC in the field, I have never had a problem.

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