Cover crops are proven to reduce nitrate loss and decrease soil erosion on our agricultural landscape, but field scale studies on phosphorus loss are still in their infancy. Drs. Antonio Mallarino, Matt Helmers, Rick Cruse, John Sawyer with Iowa State University and Dan Jaynes with National Laboratory for Agriculture and the Environment have completed two years of a long-term field study and have released their preliminary results.
The Hermann farm site south of Ames allowed Mallarino’s team to observe the effects of cover crops on phosphorus in the runoff study funded by the Iowa Nutrient Research Center.
The study is located at south of Ames on Iowa State’s Hermann Farm. The study includes replication on 12 areas ranging from one to three acres in a field that tested very high in soil phosphorus and is managed with a corn and soybean rotation. The study compares the use of winter cereal rye cover crops with and without tillage.
After two years, Dr. Mallarino observed:
“It is confirmed that cover crops reduce soil loss with tillage or no-till but mainly with tillage. Results also show that with tillage a cover crop reduces phosphorus loss. But it is not so clear that with no-tillage management a cover crop reduces phosphorus loss,” Mallarino said. “With no-tillage, there seems to be a small reduction in particulate phosphorus loss, but an increase in dissolved phosphorus loss.”
Surface runoff at the testing site is evaluated for total solids and several forms of nutrients.
Why the focus on dissolved phosphorus? The Iowa Nutrient Reduction Strategy is a technical, scientific and voluntary approach to reducing the loss of nitrogen and phosphorus to our waterbodies and the Gulf of Mexico that is home of a large hypoxic or dead zone. Both particulate and dissolved phosphorus are part of the reduction goal, however dissolved phosphorus is responsible for algae blooms and has a visible impact on aquatic ecosystems.
Caution should be taken when drawing conclusions from only two years of data. Environmental factors play a role in nutrient dynamics with surface runoff, and during the two years of the study, major rain events at the test site had been minimal with very low runoff.
“We can’t make a strong conclusion from these two years of data. There needs to additional data collection from this site and better science-based projecting so we can encourage the addition of cover crops for the right reasons,” Mallarino said.
Click here to read the full article and learn more about project.
Questions about the project contact:
Cover crops are an important tool for helping keep soil, nitrogen and phosphorus in the field – instead of our water bodies. Because they grow outside the typical corn/soybean growing season, cover crops help reduce soil erosion and take up nutrients that could otherwise leave the field. It is also the most popular practice among our Conservation Learning Lab (CLL) farmer partners.
The CLL project is studying the impact of conservation practices implementation at the watershed scale in Floyd and Story County. The conservation planning process within the watersheds has yielded cover crop contract enrollment of 675 acres and 1,081 acres, respectively, starting this fall covering 50-68% of the crop acres within the watershed.
The farmer partners chose to seed either winter cereal rye and oats. These grass species are easy to establish, relatively inexpensive and are the leading biomass producers in our cover crop research projects – keeping that soil covered (reducing the loss of phosphorus) and taking up nitrogen.
The Iowa Nutrient Reduction Strategy team reviewed cover crop research results from across Iowa and the Midwest and found that cereal rye and oats reduced nitrogen loss by 31% and 29%, respectively. Similarly, the reduction of phosphorus when adding cereal rye is about 29%, primarily as a result of reduced soil erosion. According to our RUSLE2 calculations, a cereal rye cover crop added to a no-till system can reduce soil erosion by 30-80% and can be even larger when transitioning from a conservation tillage system.
Be sure to keep checking back as we will be providing updates as the cover crops are seeded this fall!
The project is funded by the Iowa Department of Agriculture and Land Stewardship (IDALS) and the United States Department of Agriculture – Natural Resources Conservation Services (USDA-NRCS) of Iowa.
A new video produced by Water Rocks! seeks to illuminate the interwoven relationships between different pollutants that can contribute to water quality challenges here in Iowa (and beyond). Through science, emotional appeals, personal drama, and most of all, humor!, the Mississippi River Basin Watershed Support Group video explores the subtleties and complexities related to the interactions of water, soil, and pollutants in our environment.
The setting: A group therapy session.
The group facilitator: BI (biological indicator for water quality).
The support group participants: soil, phosphorus, nitrogen, arsenic, mercury, manure, bacteria, and caffeine.
Here are a few sneak peaks:
The Mississippi River Basin Watershed Support Group video was recently honored at the Iowa Motion Picture Association Awards ceremony, receiving awards in the following categories:
Direction (Medium Form)
Editing (Long Form)
Best Actress (BI/group facilitator)
This fabulous video is not to be missed! The cinematography is beautifully done and the characters are quite entertaining… if you’re anything like me, you’re going to watch it several times to catch all of the quirky humor and subtleties in the relationships happening on-screen.