This is an update to an article that appeared in the September 2006 issue of Grainews.
My Dad often talked about early bachelor settlers who lived on “faith, snuff and slough water.” In many cases on the Prairies it is a good thing they had strong faith and brought along lots of Copenhagen because the slough water often left much to be desired.
The same might be said for sloughs that are used as a water source for spraying. If the water is full of algae or sediment or stinks like an outhouse we may shy away. But if it looks clean and clear we make think it is okay. Think again. Clean, clear water can often contain loads of dissolved minerals that can cause trouble with herbicide performance, especially glyphosate.
In June, 2006 I took photos and measured the salt content on my Dundurn farm. That was repeated in July, 2013 and I took a real lesson from the readings.
When I took the photos I also measured the dissolved minerals in the water. This data was obtained directly in the field by measuring the Electrical Conductivity (EC) of the water. Benchmark data for EC (measured in uS/cm — MicroSiemens per centimetre) is as follows:
Saskatchewan River Water: EC = 350 uS/cm
Sand point wells: EC = 500 to 1,000 uS/cm
Farm wells on the Prairies, other than sand point: EC = 1,500 to 5,000 uS/cm
Sea water: 35,000 ppm TDS (Total Dissolved Solids)
(EC is a good first approximation of ppm TDS for sulphate waters , which we usually have, but above EC = 20,000 the relationship breaks down so I quote sea water in ppm TDS.)
As you select sloughs for spray water, be careful. Be sure to get an EC or hardness test before relying on the water. I have been examining and measuring salt content of sloughs for 30 years and am not much good at guessing the salt content just by looking. Agronomists should be offering this service. If I can do it most anybody can.
The photos and data tell the story. The table puts it all together so the data can be compared easily.
Juicing up the groundwater
Making the July, 2013 readings was a very serious lesson for me. I expected to document how much fresher the water was after the last few years of irrigation-type rainfall and heavy snow melt. All that fresh water should “freshen” the sloughs, right?
The large excess of rain and snow melt has really “juiced up” the groundwater flow systems. The approximate tripling of salt level in the water from 2006 to 2013 comes mainly from groundwater discharge. The west slough by the yard has a big bathtub salt ring. The high water has flooded that ring and those salts are also in the water.
Take Home Messages:
1. If you use sloughs for spray water do not expect the same slough to provide consistent water over time. Measure the EC in the field.
2. Mother Nature makes changes that can be cumulative over time — in decades — not just year to year.
3. Expect serious increases in soil salinity as we go back to the other side of the average moisture conditions.
By the way, changes in soil fertility and agronomy also have long memories and effects accumulate over time. I had a recent farm tour with Dennis Bulani in the hills north of Biggar and saw wheat crops that look like nothing I have seen before. It did not all happen over night. Good management, and especially soil fertility is cumulative. But, that is a story for another day.