Les Henry: Soil salinity and tile drainage

Can investing in tile drainage make your Prairie soil less saline and more profitable?

The idea for this subject came from a recent phone call from a farmer in west-central Saskatchewan. He was considering the purchase of a piece of land that was priced below recent sales but did have salinity problems. He was wondering about the feasibility of tile drainage to fix the problem and make the land profitable.

We have long stated that reclamation of saline land requires both tile drainage and leaching. In much of Saskatchewan, the leaching must come from irrigation as rainfall is usually insufficient to grow a crop and leave any extra for leaching.

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Several years back I had a similar question from a farmer at Glenboro, Man. Glenboro struck a note with me as Dad was born and raised at nearby Stockton. I am familiar with that area. The specific question was: “With our 18 inches of annual rain, do we have enough to do the leaching?” My answer was a very uncertain “maybe.”

Thanks to John Lee of Agvise Labs in Northwood, N.D., we now have a much better answer to that question. Just weeks ago, he sent me an update of a tile drainage project he has monitored for the past 17 years.

The site is 25 miles southwest of Grand Forks, N.D., on a sandy loam to loam soil with four to 5.5 per cent organic matter and a pH of 7.9 to 8.2. The site was tile drained in 2002 and 10 GPS referenced sites were established for annual fall sampling at zero to six inches (topsoil) and six to 24 inch (subsoil) depths.

The average April to October rain for 18 years was 18.3 inches; the annual data is in Table 1 (see below). For much of the Brown and Dark Brown soil zones of the Canadian Prairies, total average annual precipitation, including snow, is only about 12 to 14 inches with many individual years receiving much less.

Much of the leaching to remove salts would occur after crop water use stops. For Saskatchewan that is usually early August. For long-season crops like corn, the water use season in North Dakota would be longer. The September to October rainfall at the tile draining site averaged 4.8 inches but varied from 1.3 to 12.6 inches.

At the North Dakota site, salt in the surface soil has been reduced to safe levels. The subsoil salinity has changed only slightly in the 17 years. The conclusions to date from this North Dakota site (as shown in a PowerPoint slide by John Lee) are:

1. Topsoil salt levels decreased over the years as long as excessive rainfall was received.
2. Several crops now produce good yields.
3. Subsoil salt levels take longer to decrease.

4. Salinity stayed the same or increased in drier years, even with tile drainage.

John also emphasizes that the fastest payback is medium-textured and moderately saline soils. Many want to tile very saline, heavy clay soils but that is a much longer time frame — like generations.

Tile drainage at home

When we compare the rain data for that tile drainage site with the rainfall we get in the Palliser Triangle it is not hard to conclude that tile drainage will only work if much above-average rainfall occurs.

Having said that, I have a corner of a quarter section that includes 10-plus acres with salinity problems. Technically, it would be easy to drain to a road ditch to a natural drainage way that passes a few neighbours and finally dumps to Blackstrap Lake. Practically, who would want my salty water passing through and eventually dumping to a man-made lake used for irrigation and recreation?

The rainfall record for 2009 to 2019 for my site is shown in Table 2 (see at bottom).

After the 21 inches of rain in 2010, I thought that tile drains installed about 2008 would have resulted in significant desalinization. We also had fair rainfall years (for that area) from 2011 to 2016. However, much of that came in the growing season and the good crops would have sucked it up, leaving little for drainage.

After seeing John Lee’s data from the North Dakota site, I am glad that money is still in the bank. Many thanks to John Lee for doing that project and sharing the data. It has been a game-changer for me.

There are reasons other than salinity to do tile drainage such as better access for seeding etc., but for soil salinity, be selective.

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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