In July I received a book order and letter from a farmer south of Brandon. His question was: “Would the 18 inches of rain we get here be enough to provide the ‘leaching’ part of the drainage and leaching to reclaim saline land?”
We discussed the matter in a phone call and I did not have a very definite answer.
With the past two dry years, soil salinity is “in your face” on more Manitoba farms. Consequently, it was my great pleasure to give an address on saline soils to the Manitoba Agronomists Conference at the University of Manitoba, in Winnipeg last December.
It was actually a tag team presentation. When I was done, John Lee of AGVISE Labs in North Dakota presented 11 years of data from a field that had been tile drained in 2002. The site was 25 miles west of Grand Forks on a sandy loam to loam-textured soil with four to 5.5 per cent organic matter.
John had some excellent photos of the crops, year by year, starting with patchy soybeans in 2003 and including a very good corn crop in 2008. The photos were accompanied by yearly soil test data (zero to six inches and six to 24 inches). He also had monthly rainfall data. The five-year average rain (from April to October) was 17.2 inches and it varied from a low of 13.9 inches in 2012 to a high of 22.5 inches in 2002.
Some main conclusions John Lee presented were:
1. Topsoil salt levels decreased over the years as long as excessive rainfall was received.
2. Subsoil salt levels take longer to be decreased.
3. High subsoil salt levels do not affect crop growth as much as high topsoil salt levels.
4. Salinity stayed the same or increases in dryer years, even with tile drainage.
John Lee also reported on several years of data showing that elemental sulfur and gysum addition is no answer to saline soils.
So the answer I should have given the Brandon farmer is that excess rain is required to do the leaching, and that excess rain will vary a lot from year to year. A series of wet years will be good, but a series of dry years could result in some backsliding. And, the chances of getting enough rain are much better in Manitoba and North Dakota than it is in Southern Saskatchewan.
After John was finished it occurred to me that if I had installed tile drainage in my nuisance salinity at Dundurn, Sask., around 2008, the soil would be much improved by now.
But my drained water would deliver to a neighbour’s ravine (also saline), and about three miles away it would dump into Blackstrap Lake. Not a good idea. It might be possible for a group of neighbours to get together and dam the ravine to hold the salty water back. Maybe some day — but not now.
So, a big consideration is “where is the salty drain water going, and is the recipient going to like it?” Often not. †