group of farmers in a field learning about soil health from Tom Kaspar
MENTOR TO MANY: Tom Kaspar (left) discusses the soil health benefits of rye cover crops at an Iowa Learning Farms field day.

Lessons learned from a career in cover crops

Iowa Learning Farms: Cover crop expert Tom Kaspar retires from USDA.

By Ann Staudt

As the calendar turns to March, fields of cover crops starting to green up are a noticeable and welcome sign. Cover crops are one of the key conservation practices that help with water quality, soil health and reduced erosion. A good deal of our understanding of cover crops in Iowa is thanks to the work of Dr. Tom Kaspar.

Recently retired in early 2018, researching cover crops was a prime focus of Kaspar’s 37-year career as a plant physiologist with the USDA Agricultural Research Service’s National Laboratory for Agriculture and the Environment in Ames. Kaspar is a highly respected voice when it comes to outreach on cover crops, readily willing to speak at farmer field days, workshops and conferences across the Midwest.

In addition, Kaspar is a founding member of the Midwest Cover Crops Council. He’s also shared his perspectives via Iowa Learning Farms webinars and the Conservation Chat podcast.

Founding fathers of cover crops in Iowa
While cover crops were an integral part of Kaspar’s work, his initial research in the 1980s was actually focused on no-till farming and soil compaction. His entry into cover crop research came a decade later, in 1990, and expanded gradually over time.

Today, Kaspar is widely recognized as one of the “founding fathers” of cover crops in Iowa, with his studies being some of the longest continuous cover crop research across the Midwest. Over the years, Kaspar’s broad, collaborative research has investigated many different facets of integrating cover crops in farming operations. His studies have focused on impacts to water quality, particularly the potential for reducing nitrate in tile-drained landscapes, mitigating soil erosion, improving soil health and helping us better understand interactions with crop pathogens.

Lessons learned from cereal rye studies
Much of Kaspar’s cover crop work has been focused on cereal rye in corn-soybean cropping systems. Consider the following key lessons learned from Kaspar’s long-term cereal rye studies in Iowa:

• Over time, rye cover crops increase soil organic matter. After 10 years with rye cover crops, soil organic matter, particulate organic matter and potential N mineralization were found to increase, particularly in the top 2 inches of soil. Soil organic matter changes are not easy to measure, but over time, soil health improvements have been observed.

• Soil aggregation improves with rye cover crops. Large stable soil aggregates create spaces that allow movement of air and water. By improving aggregation, cover crops help to retain soil moisture and nitrogen, adding resiliency for crops in times of variable precipitation.

• Rye cover crops decrease runoff and erosion. With rye cover crops, less overall runoff and less erosion were observed after an hour of rainfall compared to no cover crop. Rye plant material protects the soil from raindrop impact and promotes improved infiltration, and the cover crop roots hold soil particles in place.

• Earthworm populations reflect improvements in soil health with cover crops. The common nightcrawler, Lumbricus terrestris, was found in greater abundance following a rye cover crop — 38% more than with no cover crop. Earthworm population increases serve as an early biological indicator of soil health.

• Cover crops capture nutrients in the soil that could be lost. In numerous studies, Kaspar and colleagues found that rye cover crops reduced nitrate concentrations in tile drainage water by 20% to 40%. Cover crops are one of the key in-field conservation practices called for in Iowa’s Nutrient Reduction Strategy, effective at reducing both nitrogen and phosphorus export.

Mentor to many ISU students
In addition to his outstanding research and outreach contributions in the world of cover crops, Kaspar has served as a mentor to numerous undergraduates and graduate students. He’s also served as a mentor to fellow researchers over the years.

“I am so grateful to Tom for his guidance and collaboration as we’ve worked to investigate the relationships between cover crops, earthworms and soil health,” says Ann Staudt, assistant program manager with Iowa Learning Farms. “His ideas and insights are invaluable as we strive to develop more effective means to demonstrate and communicate the benefits of cover crops.”

Kaspar’s research and outreach efforts have played a key role in bringing about increased cover crop adoption in Iowa and beyond. The seeds have been planted and carefully tended. Together, we’ll strive to build upon the strong foundation that Kaspar has laid with cover crop work across the Midwest.

Staudt is assistant program manager with Iowa Learning Farms.

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