A long-term, Illinois Nutrient Research and Education Council (NREC) funded project identifies conservation practices benefiting nutrient loss reduction.
During a 10-year study at Southern Illinois University (SIU), researchers have examined three main cover crops, cereal rye, hairy vetch and an oats and radish mix, along with no-till and reduced tillage. They aim to understand how these methods affect nitrate leaching, phosphorus stratification, soil properties and crop yields.
“We wanted to mimic what some of the producers were interested in in terms of cover crops,” said Karl W.J. Willard, acting dean for the SIU College of Agriculture, during Illinois NREC Investment Insights Live. “We have cereal rye in front of the soybean, and then hairy vetch and oats and radish in front of corn, to see how this system functions in terms of water quality and soil quality. And then we overlaid that too with no-till and reduced tillage.”
The research is conducted on SIU test farms, where tiling is not present. Therefore, pan lysimeters were used to measure nitrate and phosphorus leaching at the plot scale, since sampling at the watershed scale is a challenge in a non-tile drained region.
Nitrate Leaching
Compared to no cover crops, cereal rye reduced nitrate leaching by about 44%. However, hairy vetch and the oats and radish mix did show quite a bit of leaching. Tillage practices did not show significant differences in nitrate leaching.
“Sometimes we don’t tell the tillage story enough, but comparing no-till to reduced till, you can see similar amounts of nitrate leaving across the cereal rye by tillage, and also across the hairy vetch and oats and radish,” Willard said.
Phosphorus Stratification
Dissolved reactive phosphorus leaching levels remained similar across different cover crops and tillage. Researchers observed more phosphorus accumulating in the top 2 inches of the soil, suggesting cover crops may contribute to stratification by pulling up phosphorus from lower in the profile and then releasing it when the cover crop residue decomposes.
Crop Yields
Some test plots were above average yields in Jackson County and some were below, Willard said. Jackson County yield averages were 165 bushels per acre in 2015 and 2023 for corn and 42.5 and 50 bushels per acre for soybeans in 2016 and 2024.
“There is some potential for yield drag with cereal rye in front of soybean, not in all the plots, but definitely, some of those indicate there’s probably an impact on the cereal rye,” Willard said, adding that corn planted after hairy vetch and oats and radish mix didn’t show a yield penalty.
Willard plans to continue the long-term study and launch another one on his existing plots to investigate the timing of hairy vetch termination.
