In case you missed it, this past week’s Iowa Learning Farms webinar offered an excellent overview of the research findings related to the potential of winter cover crops to reduce nitrate leaching in corn and soybean cropping systems. Dr. Tom Kaspar, plant physiologist with the USDA-Agricultural Research Service, shared results from numerous studies that show the ability of cover crops to reduce nitrate concentrations and loads in tile drainage water.
The press headlines about nitrates and water quality are seemingly ubiquitous, and Kaspar provided solid data that help to paint a complete picture of the challenges and opportunities. Our land uses have changed dramatically, and over the past 60-70 years, our cropping systems have likewise changed dramatically with significant reductions in small grains, hay and perennial vegetation. With corn and soybeans having a 7-month brown gap when they are not actively uptaking nutrients, that leaves a significant amount of time with nutrients vulnerable to leaching.
However, Kaspar’s research clearly demonstrates that cover crops help transition that brown gap to a green gap, providing the ability to “capture” nutrients in the soil that would otherwise be vulnerable to leaching loss. One of Kaspar’s long-term research studies in central Iowa found that rye cover crops in a corn-soybean cropping system reduced nitrate concentrations in tile drainage water by 57%. Additional studies by Kaspar and collaborators around the state found nitrate reductions of anywhere from 20% to 40%. This variability is expected, with different amounts of cover crop growth, weather, rainfall, soil types, tile systems, and field histories.
Kaspar also pointed out that it takes quite some time for nitrate to move through the system – there is a noticeable lag effect. For instance, Kaspar and collaborators found that nitrate concentrations in subsurface tile drainage continued to decrease through the summer, long after spring cover crop termination.
Check out the full webinar, Lessons Learned from Using Cover Crops to Reduce Losses of Nitrate for 15 Years, on the Iowa Learning Farms webinar archives page. And to hear more perspectives from Dr. Kaspar, tune in to Episode 06 of the Conservation Chat podcast!