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Les Henry: New information on the water table and crop yields

Sloughs do tell a story about water tables

In recent years, this column has talked a lot about higher water tables and the role they play in harvesting good crops on years with low rainfall.

The United States has maintained the system of land grant universities that are directly tied to the land and deal primarily with research that has a bang at the farm gate. Since 1979, I have been a member of the American Society of Agronomy (ASA), Crop Science Society of America (CSSA) and Soil Science Society of America (SSSA), and I pay a modest fee each year for complete online access to all the publications.

There is still one publication that comes regularly in the mail. The May 2020 issue of CSA News, the official magazine for members of the ASA, CSSA and SSSA, included an article by D.J. McCauley talking about modelling. Sotirios Archontoulis of Iowa State University leads the project and was finding that corn yields exceeded modelled values in dry years.

The same slough as above, but seven years later on August 24, 2020.
photo: Les Henry

A direct quote from Archontoulis was, “The water table provides an additional source of water that can affect plants and soil processes in different ways. It is something we’ve ignored in the past when we were doing predictions.”

I have since established email communication with Archontoulis and we are definitely on the same page. His calculations for Iowa show that the water table credit can be up to 90 bushels per acre for corn. The water table can supply one to six millimetres per day during dry periods. That is huge, and the difference between a crop and not in a dry year.

Temperature is a big factor

For many years, what has saved our bacon in the past has been a cool July (See Table 1 at left). Long-term climate data actually shows that July is cooler. This year has seen temperatures of 30 C or higher on several days. That, combined with soils not full of water, has seen crops go downhill fast.

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I have often said to younger folk, “When a crop runs out of water in the subsoil it is all over but the shouting in a few hot days.” I have seen it in years long ago. That came to pass this year in some areas.

In 2015 on my farm, the May and June rain totalled only 1.8 inches but the crop never suffered. It was dry until July 28, when a 3.6-inch rain sealed the deal for the year. The soil reserve was good and water table was high on parts of the land.

In 2020 we had limited soil moisture reserves. From May 1 to July 8, we had 5.7 inches of rain. A crop tour on July 13 gave great promise. In the past seven weeks, we have had no useful rain — only drabs of one to three-tenths of an inch, which is gone by noon the next day and adds nothing. When the hot days came, crops went back fast. Early-seeded peas are running 40 bushels per acre, but some late-seeded wheat and canola will be a different story.

Sloughs, sloughs and more sloughs

Sloughs are a huge nuisance to grain farming. Not only is it land not seeded, but they mess up seeding and are a constant source of weeds that keep infesting clean fields.

However, they do tell a story about water tables. The water level in a slough is the water table at that location at that time.

Maude and Jake (my favourite geese) appeared on that slough each spring in the wet cycle. They nested in a grassy area near the slough. By and by, Maude and Jake brought offspring to the quarter to nest near sloughs on the southwest corner of the quarter. It was all rather fun to watch.

You might ask, “How does he know that?” Truth be told, I am not sure but it makes sense to me. In recent dry years they have all gone to wetter grounds.

At this time there is only one slough on the whole quarter with any water left and that will soon be gone if the drought does not break soon.

Thus, as you think about the water table on your farm, keep an eye on the sloughs for a clue. It is my hope that young agronomists who now install soil moisture probes will soon add water table wells to the mix so you have actual data.

Long-term water table data

Thanks to the late Bill Meneley (1933-2000), there are many Saskatchewan observation wells that show long-term trends. Those with Henry’s Handbook can read about Bill on the dedication page.

I interpret that data as a 30-year net cumulative water deficit from 1975 to 2005 leading to water table decline. The big snow of 2005 and subsequent wet years led to a sharp rise in the water table to a peak in 2016. In recent years, it has dropped back to the level it started at in 1975.

There is also a shallow observation well at the University of Saskatchewan Goodale Research and Teaching Farm near Saskatoon. It was not installed until 1974 but the parallels with the Melfort well are amazing. Observation wells are a great way to document Mother Nature’s cycles (See Figure 1 below).

Figure 1: This is the hydrograph for a 35-foot observation well near Melfort, Sask., from 1967 to 2020. To get the data for this well and many others go to wsask.ca and hover over Water Info then click Observation Well Network.

Thoughts for the future

I think it might be possible to make a three-province map with a water table legend with three simple categories:

1. The water table is a factor in crop production in many years. Thick black soils would fit this category. They are thick black in part because water tables keep plants going during droughts.
2. There is no near surface water table and, hence, it is not a factor in cropping. This would include areas like the Milden, Sask., area where I was raised. There are almost no shallow bored wells on the water well maps we made as part of soil salinity work in the ’80s and ’90s.
3. The water table is a factor only in very wet cycles.

That is on my “to-do” list for this winter.

About the author

Columnist

Les Henry

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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