Research Highlights

Soil Moisture is Key When Terminating Rye and Planting Soybeans

By Carol Brown

Using a winter rye cover crop prior to soybeans can play a valuable role for farming success. Learning how these two crops can work even better together in North Dakota is where Michael Ostlie is focusing his research.

The research agronomist at the North Dakota State University Carrington Research Extension Center is studying how soil moisture can affect soybean growth after a rye cover crop. The project is supported by the North Dakota Soybean Council.

“We know that winter rye and soybeans complement each other very well,” Ostlie said. “In previous research, some years it was fine to plant soybeans into living rye and other years there were yield penalties. We concluded that the biggest driving factor was water availability.”

Ostlie and his research team are finding that paying attention to soil moisture levels when terminating rye and planting soybeans may be more important than when traditional calendar dates dictate.

“In one study, the soil reached a 2-inch moisture deficit in the top 2-feet, which impacted soybean yields,” he said. “Even when we recovered the moisture, the damage had already been done.”

The research team terminated the rye cover crop plots at seven different dates, with soybeans planted at the fifth and sixth termination dates. One termination was after soybean planting and a non-terminated rye check plot was included. They measured soil moisture weekly at four depths, then correlated the data with soybean growth and yield.

In 2019, the study showed rye peak water usage occurred after most of the terminations were completed and with no effect on soybean yields. Only the non-terminated rye and the seventh rye termination (after soybean planting) plots affected yield (Table 1). Ostlie found the rye and soybeans peak water use times did not overlap.

Ostlie’s previous research project looked at effective winter rye management for maximum soybean potential, also supported by the North Dakota Soybean Council. Results from this study led to his focus on soil moisture.

“We assumed the earlier we planted soybeans, the safer the system would be because the rye wouldn’t be as developed,” Ostlie said. “But it all depended on rain. We had some dry early springs and ended up with yield penalties with those early plantings.”

He also found that after good rain events the soybeans planted into living rye cover crop was successful, even with the more developed rye.

“This spoiled the assumption that planting soybeans earlier into smaller rye doesn’t guarantee that we’re going to be safer,” he said. “It still holds true a lot of the time, but we wanted a better management tool for these decisions.”

They will have more data for this study after this year’s harvest is complete, especially coming off of 2019, a year with extreme weather issues in the state. 

“I expect to see more farmers plant rye this fall, especially on the prevent-plant fields from 2019, hoping to get a jump start on the biological activity in what was essentially fallow acres,” Ostlie said. “Growers here are recognizing the synergy and those who have been using rye cover crops are largely satisfied.”

A cover crop has numerous benefits. It is a good weed suppressor and provides protection from wind erosion by keeping the soil covered. If farmers adjust rye termination and soybean planting timing based on soil moisture, they could add another benefit shown on the yield monitor.

Published: Nov 17, 2020