Dry land salinity is a major problem on the Prairies. In Alberta, about 1.6 million acres of dry land are impacted by secondary salinity. On average, Alberta crop yields are reduced by 25 per cent annually because of the problem. Salinity also impacts 3.3 million acres in Saskatchewan and 0.6 million acres in Manitoba as well.
Research shows, though, that soil salinity can be managed with cover crops. The problem, said Caley Gasch, a soil scientist from North Dakota State University, is that the salts are present in geologic material, and depending on their proximity to the water table and landscape patterns, the salts move up with groundwater. Its movement is very much tied to the climate cycles.
“In dry years, the salts can actually move down into the profile, and then move up, depending on the time of year,” said Gasch. “Over the longer term, those salts can migrate and become a problem or less of a problem, depending on water movement.”
Lately, though, there have been a lot more salty patches showing up.
Water management is the best way to manage salinity problems. “The salts are soluble, of course, so if there’s a site that has salt on the surface and if there’s drainage, then that’s a good opportunity to take advantage of water movement in those areas,” said Gasch.
The best opportunity to do that is in the spring when there is a lot of snowmelt. The free water will dissolve the salts and move them down into the profile. “The trick then is to keep them down,” she said.
Using a cover crop
Cover crops have been a really good tool to aid in this movement of salt. They help provide residue on the surface over the winter, catching a lot more snow. In the spring, when that snow melts, the salts will be flushed down.
The key is choosing crops that are saline tolerant and overwinter well in harsher climates. “We’re using a lot of cereal rye or winter rye in our region because it’s about the only thing that will overwinter in terms of a cover crop,” Gasch explained.
When the crop starts to grow again early in the spring, it uses water, increase evaporative demand and keeps the water table fairly low so the salt don’t move up.
Gasch is currently conducting research to quantify the water use and movement, and the movement of the salt.
There aren’t really any cover crops that take up the salt. There are plants that are salt-tolerant and will take up salts, but they’re not used as cover crops. Barley is fairly saline tolerant and makes a good option for those who don’t want to use cereal rye. There are also some salt-tolerant alfalfa varieties available.
Gasch suggests taking severe saline patches out of production for a year or two. She suggests instead planting barley or a perennial grass that’s more tolerant to salt. It will help lower the water table and keep the salts down.
Kevin Elmy, a farmer from Yorkton, Saskatchewan, has been playing with cover crops since 2008. Some years ago he started Cover Crops Canada, a website dedicated to bringing together cover crop retailers.
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Elmy says before choosing a cover crop you need to know why the salinity is there in the first place. The next step is getting that ground covered to stop the evaporation or use that water before it comes up out of the ground. “The trick is what species, when do you seed it, how do you seed it, and how do you further manage it?” he said.
Elmy uses sugar beets in wet saline areas. If it’s drier, he uses safflower, sunflower, a little radish and sometimes turnip. An avid proponent of multi-species mixes, he’ll sometimes throw in some sweet clover, fall rye, sorghum, Japanese millet and barley.
“One of the keys, in my mind, is that you want to have these deep-rooted species,” said Elmy. “Because we want to create pores in the soil to allow those salts to leach out. And we want to have tubers in those blends because tubers are going to bring up a lot of calcium in those saline areas.”
Back in North Dakota, Gasch and one of her extension partners, Abby Wick, are working on other saline-related research. Working closely with entomologists and soil scientists, they’re looking closely at soil ecology and using cereal rye in corn-soybean rotations to manage these saline areas. “But we’re really primarily interested more in the changes in the biology that the salty areas may have,” she said.
“We have some preliminary data that indicates that those salty soils have different insect communities, and they certainly have different hydrology and chemistry,” she said. “We think that they potentially have very different biological communities in general. They could be sources for different soil-bourne pathogens or pests or they could be refuges for beneficials. We just don’t really know.”