Farmers know where their fields could use some drainage, where tile systems might be a solution. But deciding whether or not it will make them money is a tougher choice.
What makes a field a good candidate for a tile investment that will provide a clear return on investment?
Thomas Scherer of North Dakota State University is an expert on subsurface drainage. He conducts research on tile drainage and delivers presentations for organizations interested in the production practice.
He said the first step is to find out if an elevated water table is at the root of a field’s water woes.
“Just because you got stuck in some parts of the field doesn’t mean that it’s a high water table,” Scherer said.
He says agrologists and farmers should work with whomever knows the field the best and longest, to understand “if they actually have a high water table.”
He’s seen significant tiling investments wasted in fields that were having problems in a wet cycle, but little or no water came out once installation was complete because a high water table wasn’t the issue.
Finding out the scale of a high water table problem across a field is important to help determine whether a pattern or targeted style of project is best suited to address the water issue.
“Pattern tiling is fairly common on relatively level fields because the problem is persistent right across the field. When you get into areas where there is a little more slope, they use targeted drainage where you identify the areas where you have water interfering with field and harvest operations,” Scherer said.
Bruce Shewfelt of PBS Water Engineering has worked with tile drainage in Manitoba since the mid 1990s and he said a good first step is to look at the soil survey maps.
“Look at if it’s rated poorly or imperfectly drained as opposed to well or rapidly drained. Look at the actual soils themselves, look at the soil profile to see if there are signs of the soil being saturated for extended periods of time,” Shewfelt said.
A simple way to understand the water flow of your soil is to use a slotted piezometer, which is a slotted pipe that’s installed three or four feet deep so that the water table can be periodically measured, possibly with an automated data logger.
“You can see what your water table is doing. It comes up in the spring, goes down in the fall, and you can see what points in time it might be impacting your crop,” Shewfelt said.
“Other indicators such as crop yield and salinity might be associated with extended periods of higher water tables. You put all those things together and kind of come up with a zoning of your field.”
Agronomists know their way around yield and EM maps and they usually manage the soil testing program, so it’s within their scope of work to tweak the sampling to help pull out zones in a field where tile will improve profitability.
Developing zones where a high water table is likely affecting field productivity for the farming customer will provide them with a good understanding of what their field needs before conversations with tile drainage contractors begin.
Scherer said the soil type on the surface isn’t always what’s below the surface where tile is installed, so a high resolution look at the soil profile in the specific areas being considered is often needed, including if and where the field has sand or clay layers and exactly where the elevated levels of salinity are.
For instance, if there is a heavy clay layer down where the tile pipe is installed, the tile will need to be installed closer together than if there is a sand layer at that depth.
He said there are two main reasons why growers in North Dakota and the Red River Valley had tile installed. The first is excess water prevented field operations and the second reason is excess precipitation over the last 20 years raised the water table and brought dissolved salts to the surface.
“They’ve always been there but when you go through dry periods they just get pushed down. When you get the wet periods and the water table rises to the surface and previously farmable land becomes very difficult,” Scherer said.
He said there are plenty of areas in Saskatchewan, southern Manitoba and northern parts of South Dakota where pieces of shale were deposited by glaciers.
The shale is the remnants of an old inland sea so they are full of salts, and when water comes into contact with them some of these salts go into solution, Scherer said.
Just focusing on surface drainage won’t solve salinity issues, because the minerals are down below. Scherer said to prevent the salts from rising to the surface it is necessary to remove them through subsurface drainage before they have a chance to surface. Another way is to plant a crop with deep roots, such as prairie grasses that use all the water in the top six to eight feet and prevent the water table from rising up to the surface.
Shewfelt said there are situations where elevated salt levels are associated with deeper upward movement of the minerals, and these scenarios are much trickier to tackle with tile.
In many instances it is possible to turn some salinity problems around with tile drainage, but in order for this to occur there needs to be an adequate amount of water flowing through the tile.
Tiles can collect salts that are coming up towards the surface in the groundwater and precipitation will dissolve salts near the surface and wash them away though the tile.
Shewfelt was involved with work near Winkler, Man., from about 1995 to 2010 where the team conducted EM38 mapping of a potato producer’s field with tile drainage.
“We did the EM mapping, that was a measure of salinity in the field over time, and initially there was something in the order of 20 percent of the field that was slightly too weakly saline. By the end of that 15-year period it was down to about five percent,” Shewfelt said.
When it comes to understanding sodicity versus salinity in fields, the University of North Dakota has studied the feasibility of reclaiming sodic soils, including with tile drainage, and it found tile drainage by itself typically is not the solution for sodic soils and that soil amendments are usually required as well.
Another important step in the preliminary investigation into the suitability of tile drainage to manage a drainage problem is to make sure there is a place for the water to flow.
“You have to look at where the natural drainage is. Where does the water go that runs off that field currently? There are a lot of places in southern Manitoba and Saskatchewan where they don’t have an outlet for the water,” Scherer said.
“Not only know where it’s going, but it has to keep moving. The water that comes off, you don’t want it. Some of the biggest problems in tile drainage is people tile and then they dump into neighbours and it ponds up.”
In areas where there is currently no outlet for tile water to flow, Scherer said lift pumps are now economically viable.
“You can buy pre-set up installations from both AMS and Prinsco to lift water if it’s difficult to get it out. The big cost is putting them in, the pumping cost is not that great,” Scherer said.
“The actual electrical lifting cost in this area is about $6 an acre, and that was during some wet years.”
Shewfelt said growers should be aware that when they put tile in the ground they change the hydrogeology of the field, with typically less surface runoff and more water flow through their soils.
“As the water flows through the soil you can pick up nutrients, mainly nitrogen, as opposed to surface runoff that contains phosphorus. You would also, in the case where you have saline soils, you could be picking up salt load,” he said.
From a salt perspective it’s a managed issue because you’re trying to remove salts from the root zone, but you’re not typically removing salts from deeper down.
“So it’s a matter of understanding how much salt may be discharging out of your tiles and where it’s going to end up. Typically that will dissipate over time,” Shewfelt said.
“But that initial flush of salt, you want to make sure that it’s getting diluted into the water system downstream.”
The minerals dissolved in tile water will stay with the water as long as it keeps moving, whereas they will be deposited where the water stops and evaporation occurs.
A lot of the best management practices coming out of the upper Midwest states target nitrogen or nitrates in the tile water, because there are millions of tiled acres in these states and they have a nitrate issue in their surface water from tile drainage, among other things, Shewfelt said.
“So they’re specifically targeting practices to reduce that, and that would be saturated buffers, wetlands, controlled drainage and bioreactors.”
Saturated buffers divert tile water into shallow laterals that raise the water table within the buffer, where perennial vegetation uses some of the water and thus slows water outflow from the tile.
Shewfelt said he is not aware of any laws in Canada that regulate the water quality of initial flow of tile water.
Shewfelt helped develop fact sheets on beneficial management practices for agricultural tile drainage in Manitoba for the Prairie Agricultural Machinery Institute (PAMI), including a section on nutrient management.
He said growers should be aware of how tile can potentially affect their fertilization program, especially when it comes to nitrogen inputs.
“If your water table is high and your tiles are running and if you apply fertilizer and it rains, then you’re going to wash some of that out. The more timely you can put your fertilizer on relative to crop use the more efficient it is,” Shewfelt said.
He said losses of applied crop nutrients through tile is a much bigger issue in the upper Midwest states because their tiles are running up to 11 months of the year, while in Canada soil freezes over the winter which stops nutrient losses through the tile.