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DIY: Installing water table wells

With water in the soil, we can survive on little rain. Learn how to measure what you have

2015 will go into the books as a very different kind of growing season. In central Saskatchewan we started off with soil completely full of water after a big dump of snow on April 26. My rain gauges showed 2.5 inches of water when it all melted.

And then Mother Nature turned of the tap completely. It was dry, dry, dry. May total: 0.3 inches. June total: 1.6 inches. All in dribs and drabs of 0.2 or 0.3 inches. July: same thing until July 28 when the drought broke and gave us 3.6 inches.

The cold May with frost events was more responsible for poor early crop growth and poor hay crops than was the drought. (Note: central Alberta was different — they had no subsoil reserve). My canola crop looked terrible until it warmed up in June and then it took off like a rocket.

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In annual crops most serious water use happens somewhere between mid June and late July. In July, I had canola with flowers up to my chin and on high ground the soil was drying down as the crop sucked the water. In the end the crop sucked the top two feet bone dry, the third foot wasn’t far behind and the roots finished off in the fourth foot.

But, in lower land there were places with canola flowers up to my chin and the soil was still full of water. On July 18 I installed water table wells at two locations in the crop.

A diagram on page 107 of Henry’s Handbook of Soils and Crops shows how soil moisture, crop water use and the water table interact. Since the book was published I have established another “Rule of Thumb:” When a soil is at field capacity moisture to the water table and more rain comes, each additional inch of rain brings the water table up six inches on sandy soils, eight inches on medium soils and 12 inches on clay soils.

Installing water table wells in three easy steps

  1. Gather the appropriate equipment and supplies.
  2. Dig the well. Start with the four-foot foot auger and add extensions as required. But, only do 1.5 turns and then pull out the auger and empty. Do not screw it in too far — you will kill your back reefing on it. In glacial till you will hit rocks. If the soil is moist you can wiggle around small rocks. If you hit a big one, start over. I have seldom had to start over.
    In clay soil you can auger quite a way below the water table and no water will be visible. When you are well into water table you will know.
  3. Install the well. Set the top of the pipe to correspond to the natural ground level so no correction for “stickup” will be required. Mark with a flagpole and GPS for permanent record.
    At age 75, I can install such a well in less than half an hour, so you kids should have no trouble installing many in a day. This is not something a farmer with 10,000 acres is going to do but most have consultants that could easily do it.

Measure water level and maintain a record

I use a Solinst water well sounder to get data to the nearest cm. This item set me back $700 — I use it in my consulting business. But young smart techies can come up with much cheaper ways to measure the water level. Leave the well for a couple of days before measuring so equilibrium can be established after the “trauma” of installation.

When the well was installed the crop was doing just fine, thank you, on very little rain (see the photo of the auger in the hole, taken on July 18 in the Gallery link above.) And, the soil probe went into the moist soil like butter, even at the soil surface. Clearly the water table was involved. The water table was at 1.82 m and capillary action would suck water up to where the plant roots could access.

south well data-07182015

Subirrigation: complements of Mother Nature

Weather forecasts have improved tremendously. These days, when a forecast for significant rain comes along it usually happens. I was careful to do a measurement of water level the day before a rain forecast. July 18 was our first real rain of the season. It was nice gentle rain with little runoff.

If you closely examine the water level and rain record shown in the table, you will see that the theory works out quite well in practice. By the September 5 to 7 rain the crop was off, so the 1.4 inches of rain brought the water table up 17 inches.

All of this is very low tech, but it works. How can you plan your 2016 crop if you do not know the details of the gifts Mother Nature is providing? In our area we know that most of next year’s moisture is in the ground and we can plan accordingly.

When it did not rain in June and July 2015 the Global Warmers were all screaming drought and disaster. Who had checked Grainews March 13, 2015 for the Stubble Soil Moisture map as of November 1, 2014? In west-central Saskatchewan and much of central Alberta the map showed that early and regular rains would be needed. Elsewhere, not so much. We survived nicely on what was in the ground.

The Feds and others are excited about SMAP (Soil Moisture Active Passive), a new project that is going to use satellite data to map soil moisture. But, guess what? It measures to a great depth of five to 10 cm on bare ground. If a crop is on the land the depth of measurement is even less. Surface moisture is here today and gone tomorrow. Water in the subsoil is like money in the bank. The only complete Prairie Provinces map of subsoil moisture is that produced each year right here in Grainews.

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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