Research HighlightsStudy on Managing Salinity with Cover Crops in North Dakota has Unexpected Outcomes
By Carol Brown
Farming in North Dakota has advantages including flat land and cooler temperatures that are agreeable to a variety of crops. But there are also challenges. Agronomists and soil scientists are exploring how to help farmers adapt to millions of acres tainted with salts and sodium in the soil, which is not conducive for growing many commercial crops.
Assistant Professor of Soil Health at North Dakota State University, Caley Gasch has been leading a three-year research project, funded by the North Dakota Soybean Council, to help farmers manage soil salinity using a cereal rye cover crop.
“The salinity in our soils doesn’t go away, but we can use different practices to help alleviate the problem, and it all relates to water management,” Gasch says. “Our research team believed that cover crops would use extra water in depressional parts of a field, which is where the salinity occurs. This would help dry out the soil profile, allowing for precipitation or snowmelt to leach the salts lower than the rooting depth of the cash crop.”
The salts are dissolved in water and move with the water in the soil profile and across the landscape. When the water leaves the soil, it leaves the salt behind, Gasch says. Increasing the amount of vegetation using water from the soil profile is an effective way to prevent these salts migrating to the soil surface.
The research project was conducted with four cooperators using a corn–soybean rotation in three North Dakota counties over three growing seasons. The farmers were using no-till and were not regular cover crop users. The project included the study of insects and the soil microbial community in these fields. After multiple years, Gasch had some unexpected outcomes.
“Honestly, we were disappointed with the cover crop performance,” she says. “For the first two years, we had good cover crop growth but didn’t see any difference in the soil water content between the cover crop and no cover crop treatments. We also didn’t see the salinity change.”
Gasch says the cereal rye was seeded at 40 lbs/acre for the first two years. In the third year, they doubled the cover crop seeding rate but still didn’t see any salinity differences.
“We were underwhelmed with the impacts of the cover crop on managing water and alleviating salinity, however, we found some interesting results in other portions of the study,” Gasch says. “We’ve learned the entire ecosystem in saline soils is very different than in the non-saline soils. Microbial communities are functioning differently, and the insect community is very different.”
The dataset acquired in these components are complicated, Gasch says, and they’re still studying it all. But she was confident in saying there is a completely different microbial habitat in the saline soil areas.
Gasch learned some other lessons from this study as well. Rather than inter-seeding a cover crop, she believes these salty and wet soil areas require a more heavy-handed approach.
“We recommend zoning out these areas that aren’t productive for corn, soybeans or other cash crop, and manage them differently,” she explains. “A perennial cover crop mix with a lot more vegetation would manage the extra water better in these spots.”
She also recommends cover crop management tweaks as a result of the study. They inter-seeded rye into the corn canopy, which grew more biomass as it had more time to grow. They waited until just before leaf-drop to seed the rye into soybeans, and Gasch says, it didn’t have much fall growth.
“When seeding into corn, producers can do this as early as July or August, allowing more time to get the cover crop established,” she says. “The next spring, farmers can plant soybeans into the living cover crop. I don’t believe it is cost-effective to inter-seed cereal rye into soybeans as the growth time is limited and the rye doesn’t perform as well going from soybeans into corn.”
Another outcome Gasch saw wasn’t related directly to the research project, but was still a benefit, nonetheless. The four producers she worked with have expanded their cover crop usage to all their acres.
“These farmers were experimenting with cover crops prior to this study, and over the years I’ve been working with them, their comfort level has increased,” Gasch says. “They were comfortable with doubling the rye seeding rate in Year Three and now they are trying new and different things.”
Cover crop usage is growing in North Dakota because of their numerous benefits, including the reduction of soil erosion. Gasch has found that using cereal rye to aid with soil salinity should not be a producer’s main goal. After she completes her studies on the microbial and insect communities in saline soil areas with cereal rye, she may yet discover even more cover crop benefits.
To find research related to this Research Highlight, please visit the National Soybean Checkoff Research Database.