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Les Henry: Is your slough water safe for cattle?

If you’re looking to sloughs for water, screen them with an EC meter to be safe

As the drought drags in many parts of the Prairies, there is great concern about crops. Many areas started the season with little subsoil moisture reserve and most areas have had too little rain. In some cases it is almost none — at my Dundurn farm, the total rainfall for the year to date as of June 16 was one inch. The biggest single rain event was 0.3 inches.

The situation is bad enough for stubble jumpers but it is the cowboys that have serious concerns. The cropland will sit there unharmed. Since we adopted zero-till practices the windy days in May no longer lead to dust storms and land changing hands in the air. But the cows wake up each day hungry and need something to eat and drink. This piece is all about the drink.

Previous columns have shown slough water data from my Dundurn farm. I now have 17 years of data showing how sloughs change over time. The real worry is water that is too salty — particularly with sulphate salts.

Field screening

Slough water can be screened using an EC (electrical conductivity) meter.

An EC meter is easy to use and provides a very useful and cheap screening in the field with an instant result. For many of our surface waters, EC is a useful approximation of TDS (total dissolved solids). There is a detailed account of TDS and EC is in Henry’s Handbook of Soil and Water. Readers who have the book can check out pages 124 and 125. EC units are microsiemens (μS)/cm corrected to 25 C.

My knowledge of animal science runs to almost zero and the situations that can cause problems have many variables. What is safe in cool weather when water intake is low might be a problem on a scorcher when cows need a lot of water. But, a useful guideline for initial screening is:

  • EC < 5,000 μS/cm: probably OK but as value approaches 5,000 be vigilant.
  • 5,000 to 10,000 μS/cm: increasing problems possible.
  • 10000+ μS/cm: look for another water source.

Dundurn data

Table 1 (below) shows EC data from three nearby sloughs, from 2006 to 2019. These sloughs are very close to one another, as shown in the Google Earth map. The data is easy to interpret. All values are rounded to the nearest 25. Slough #1 at a high relative elevation has remained good through the wet/dry cycle. Sloughs 2 and 3 became questionable early in the dry cycle and slough 3 is now nearly dry and would be unacceptable. The winter of 2017/2018 with about 30 inches of snow resulted in some improvement from the spring snowmelt. The cool weather this year has helped.

All of those sloughs were dry at the turn of the century and water tables and pressure in aquifers was low. The big snowmelt of 2005 left very good water. As water levels rose, sloughs 2 and 3 flooded the salt ring. That and groundwater discharge actually increased the salt level.

The past few dry years have increased the salt to dangerous levels for cows. Note the large increase over summer and fall in the dry years of 2017 and 2018.

Slough No. 4, shown in Table 2 (at left), is a different story. It was actually a dragline dugout built many years ago. In the big drought of 2002, some cows were removed just in time and in great distress. In fall 2002 my neighbours were looking for locations to dig dugouts as sloughs were dry. We used the trusty EC meter to help with that project and I measured dugout No. 4 that had been the source of nearly fatal water. At that time the EC was 14,750 which was very much too high and nearly proved fatal. Water samples were taken to the College of Veterinary Medicine at the University of Saskatchewan and the sulphates were off the chart (I do not have the actual value).

That quarter section was subsequently bought by my neighbours and I have followed it occasionally. On June 13 this year we checked that source and other nearby pastures. By fall 2018 I was worried about how fast it might deteriorate but the spring freshet had improved it somewhat. The cool spring also played a role. It is a small source so with hot weather and 60+ stock it could change fast.

Sask Ag offers help

In Saskatchewan, the Saskatchewan Ministry of Agriculture Regional Offices have geared up to be able to help farmers with questions about possible pasture water sources. Contact your regional Sask. Ag. office for more information.

We hope that by the time this hits your mailbox many of you will have had rain and the problem will have gone away. At mid-June, some areas had had an inch or so. But, much more will be needed to rescue crops and pastures this year in many areas.

About the author

Columnist

J.L.(Les) Henry is a former professor and extension specialist at the University of Saskatchewan. He farms at Dundurn, Sask. He recently finished a second printing of “Henry’s Handbook of Soil and Water,” a book that mixes the basics and practical aspects of soil, fertilizer and farming. Les will cover the shipping and GST for “Grainews” readers. Simply send a cheque for $50 to Henry Perspectives, 143 Tucker Cres., Saskatoon, Sask., S7H 3H7, and he will dispatch a signed book.

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