Recent Midwest Research Publications

Iowa Learning Farms

In partnership with twelve farmers across the state, Iowa Learning Farms and the Iowa Cover Crop Working Group are conducting the longest running on-farm cover crop research and demonstration project in the state of Iowa. Established in 2008 and 2009, these on-farm sites include randomized, replicated strips with and without cereal rye cover crops, all managed within corn/soybean cropping systems. Data collected included above-ground cover crop biomass near the time of spring termination, crop yield, soil health measurements, and earthworm midden counts. Key project findings to date:

  • Farmers reported that in 55 of 59 site-years, a properly managed cereal rye cover crop had little-to-no negative effect on corn and soybean yield. Soybean yield actually increased in 7 site-years and corn yield increased in 2 site-years.
  • After five years of a cereal rye cover crop, we found no measurable differences in soil health variables between the strips with and without the cereal rye cover crop at individual locations.
  • However, earthworms can serve as early indicator of soil health. Looking at the common nightcrawler (Lumbricus terrestris), our 2016 midden count data indicate a statistically significant difference of 38% more earthworms with a cereal rye cover crop.

Rye Cover Crop Project Webpage

Earthworm Midden Project – Blog Post and November 2016 Webinar Link

Additional Cover Crop Resources from Iowa Learning Farms 

Presented at the 2017 Soil Health Conference in Ames, IA.

Full poster: Exploring Soil Health and Agronomic Impacts of Cover Crops: On Farm Results

T.C. Kaspar, E.B. Moore, M. Wiedenhoeft, M. Shipitalo, Ben Knutson, Keith Kohler, Jaxon Goedken, and C.A. Cambardella

A cereal rye cover crop is one of the few cover crop species that has been consistently successful in Iowa in corn-soybean rotations. Thus, it has the most potential to improve soil health in this cropping system.  Unfortunately, there have been few studies that have demonstrated improved soil health with cover crops in corn-soybean rotations in Iowa or the Upper Midwest.  Part of the reason for this is that soil variability in most fields resulting from different soil types, landscape position, previous main crop effects, machinery operations, and crop rows often make detecting differences in soil properties affected by cover crops difficult to detect and require intensive sampling.  Also, the inherent high degree of soil health of many Iowa soils for some properties probably requires many years of cover crop use before changes are detectable.  The experimental site for this project was in central Iowa and the predominant soils are Clarion loam and Nicollet clay loam with 2% slope over the entire site.  A corn silage-soybean rotation with no till was established in 2001 and both phases of the rotation were present in each year. Two treatments were evaluated: a rye cover crop following both corn silage and soybean and a no rye (control) treatment. The rye winter cover crop was planted after silage or soybean harvest with a grain drill and killed with glyphosate in the spring.  After 10 years the rye cover crop had increased soil organic matter, particulate organic matter, and potential N mineralization particularly in the top 5cm of soil. Soil organic matter was also increased significantly in the 5- to 10-cm layer, whereas the particulate organic matter and potential N mineralization increased in that layer, but were not statistically significant.  It is important to consider that these were difficult measurements to make and over 600 cores were taken over two years in the treatment strips, which covered a total of about 1 acre.  Thirteen years after the first rye cover crops were planted, we applied a simulated rainfall of 65 mm to parts of the treatment strips and measured with the cover crop increased time to first runoff, decreased runoff after 60 min of rainfall, increased water infiltration, and decreased sediment in the runoff.  Because the rye cover crop was alive in the fall when this simulated rainfall was applied, previous cover crop water use, root enmeshing of soil particles, and rye shoots and crowns impeding surface water flow and soil detachment were probably important. Lastly, after 15 years of cover crops we collected soil samples from the surface 5 cm and found that wet aggregate stability for all aggregate size classes above 0.25 mm increased with the rye cover crop.  Better aggregate stability is often associated with increased infiltration, so this is consistent with our simulated rainfall results.  Part of the reason for our success in this experiment resulted from using corn silage rather than corn harvested for grain because it allowed for earlier cover crop planting and more cover crop growth.  Additionally, removal of most of the corn residue with silage harvest probably helped to accentuate and measure differences in soil health due to cover crops.  This study showed that rye cover crops with good growth over many years can improve or maintain soil heath of good Iowa soils.

Poster presented at the 2017 Soil Health Conference in Ames, IA.

Full poster: Using a Cereal Rye Cover Crop to Improve Soil Health in a Corn Silage – Soybean Cropping System in Iowa

J. Acharya, M. G. Bakker, T. B. Moorman, T. C. Kaspar, A. W. Lenssen, and A. E. Robertson

Cover crops provide important water and soil quality benefits, but also require farmers to make additional management decisions. One of the choices that farmers have to make when using cover crops is when to kill the cover crop relative to the expected date of planting their next grain crop. The length of this interval between cover crop termination and planting of the next crop may influence how much the cover crop grows, as well as how the subsequent grain crop performs. We performed experiments to test the effects of various time intervals between cereal rye cover crop termination and corn planting on corn seedling disease, corn growth, and grain yield. Shorter intervals increased seedling disease, and reduced corn emergence, shoot growth, and grain yield of corn following the cover crop compared with corn planted 10 or more days after rye termination or without the cover crop. The proportion of roots infected with Pythium spp. increased with shorter intervals. We also measured the proportion of roots infected by Fusarium spp., but the results were less consistent than for Pythium spp. This research is important because it shows that corn seedling root disease following a grass cover crop may play a role in decreases in corn population and yield that have sometimes been observed following grass cover crops, like cereal rye. Additionally, although a 14-day interval between rye cover crop termination and corn planting has often been recommended, this study shows that decreased corn seedling disease is one of the benefits of delaying corn planting after cover crop termination. Thus, a 10 to 14 day interval between rye termination and corn planting should be followed to realize the benefits of rye cover crops while protecting corn yield. The impact of this research is that farmers, extension personnel, crop advisors, and soil conservationists will be able to use and manage cover crops more effectively, which will lead to more cover crop adoption, less risk to corn yield, and more environmental benefits. Additionally, with this improved understanding it should be possible to develop new cover crop management practices to obtain the full benefits of cover crops.

Article Citation:  Acharya, J.,   Bakker, M. G., Moorman, T. B.,  Kaspar, T. C., Lenssen, A. W., and  Robertson, A. E. 2017. Time Interval Between Cover Crop Termination and Planting Influences Corn Seedling Disease, Plant Growth, and Yield. Plant Disease 0 0:0, PDIS-07-16-0975-RE

APS Journal article here.

Marisol Berti, Russ Gesch, Christina Eynck, James Anderson, Steven Cermak

Camelina is an annual oilseed crop in the Brassicaceae family that has been cultivated since 4000 BCE. Recently, interest in its oil, meal and the developed products has increased research in this crop. This renewed interest is evidenced by the tremendous increase in peer-reviewed publications containing the word ‘camelina’. Databases report 335 publications between 2013 and 2016, with 149 of those published since 2015. The objective of this review was to compile and summarize new and existing information in order to identify gaps in knowledge and areas for future research. This review includes the most recent publications in camelina description and origin, uses, genetics, genomics, breeding, molecular genetics, physiology, agronomic management, and ecosystem services. Although the breadth of research in camelina over the last few years is impressive, several areas that would benefit from further research were identified. The development of new uses and the refinement of existing uses from camelina oil and meal will continue to add value to this crop. Advances in genetics, breeding, and genomics will speed up the development of high yielding camelina cultivars, with improved seed quality as well as disease and insect resistance. Understanding and improving freezing tolerance in camelina will advance the use of winter camelina as a cover crop or cash cover crop in double and relay cropping systems. Better management practices and weed control alternatives will be needed to increase camelina production worldwide. Lastly, commercial development of camelina will add one more crop to the already low agricultural diversity in many parts of the world.

Article Citation: Marisol Berti, Russ Gesch, Christina Eynck, James Anderson, Steven Cermak, Camelina uses, genetics, genomics, production, and management, Industrial Crops and Products, Volume 94, 30 December 2016, Pages 690-710, ISSN 0926-6690,

Science direct article here.

Andrea D. Basche, Thomas C. Kaspar, Sotirios V. Archontoulis, Dan B. Jaynes,Thomas J. Sauer, Timothy B. Parkin, Fernando E. Miguez

In the Midwestern United States crop growth and yield are often reduced by short periods of drought during the growing season. One approach for farmers to adapt to this variability is to utilize crop and soil management practices that enhance soil water storage, which would reduce the risks drought-induced crop water stress. Some research has indicated that a winter rye cover crop grown between harvest and planting in corn and soybean rotations can increase soil water availability, but producers continue to be concerned that water use by cover crops will reduce water available for a following cash crop. In this study we made measurements of soil water storage capacity and soil water content throughout the growing season and corn and soybean growth and yield from 2008 to 2014 at a Central Iowa research site that has included a winter rye cover crop in a corn-soybean rotation for thirteen years. We found that the cover crop increased the soil water storage capacity by 21-22% in the upper 12 inches of soil and that the cover crop water use did not reduce the water available for corn and soybean growth. Although cover crops use water when they are alive and growing, after they have been terminated with herbicides in Iowa new rainfall normally replenishes soil water content. This most likely occurs because the cover crop improves water infiltration and storage and the residues mulch the surface reducing evaporation.  Corn and soybean growth and yield were not affected by the presence of the cover crop before planting. This research indicates that the long-term use of a winter rye cover crop can improve soil water dynamics and storage without sacrificing water availability or crop yield in corn-soybean crop rotations in the Midwestern United States. This should reduce producer concerns about cover crop water use in Iowa and should increase producer adoption of cover crops.

Article Citation: A.D. Basche, T.C. Kaspar, S. Archontoulis, D.B. Jaynes, T.J. Sauer, T.B. Parkin, F.E. Miguez. Soil water improvements with the long-term use of a winter rye cover crop. Agric. Water Manag., 172 (2016), pp. 40–50

Science Direct article here.

Jaimie R. West, Matthew D. Ruark, Alvin J. Bussan, Jed B. Colquhoun, and Erin M. Silva

Irrigated vegetable production dominates the landscape of the Central Sands region of Wisconsin, where sandy soil limits nutrient and water retention. Sweet corn was managed organically in 2011 and 2012 growing seasons to evaluate effects of organic N input and weed management with respect to sweet corn yield and soil N content. The first treatment factor was early season manure, including spring-seeded field pea incorporated as a green manure cover crop, pelletized poultry manure, and no manure. The second treatment factor was weed management intensity. The last factor was varying N application rate, split applied as feather meal during the growing season. There was a positive yield response to feather meal in both years with yields reaching 8.3 and 9.6 tons per acre in 2011 and 2012, respectively, with 200 and 100 lbs N per acre feather meal application, respectively. Early season manure treatments (field pea green manure and pelletized poultry manure) did not clearly affect yields despite 80 lbs N per acre applied as both manure types in 2012, and lower rates of 29 and 67 lbs N per acre applied in 2011 as field pea and poultry manure, respectively. These results underscore the well-known potential for rapid nutrient loss on coarse soil and management challenges associated with asynchrony between organic N release and crop uptake. Weed management contributed to an interaction effect on yield, with early tillage potentially controlling weeds in both treatments. This study demonstrated benefits of in-season organic amendment use, though limited potential for early season application on loamy sand.

Article Citation: West, J. R., M. D. Ruark, A. J. Bussan, J. B. Colquhoun, and E. M. Silva. 2016. Nitrogen and Weed Management for Organic Sweet Corn Production on Loamy Sand. Agron. J. 108:758-769. doi:10.2134/agronj2015.0393

Science Societies article here.

T.C. Kaspar and M.G. Bakker

Corn and soybean farmers in the upper Midwest are showing increasing interest in winter cover crops. Cover crops can improve the sustainability and resilience of corn and soybean production systems. At present, the most widely used cover crops in corn-soybean systems in the upper Midwest have been winter cereals. However, there have been isolated reports of corn yield reductions following winter rye cover crops and the risk of corn yield reductions will reduce the likelihood of farmers adopting cover crops. Although there are many possible causes of corn yield reductions following winter cereal cover crops, we suspect that there may be differences among winter cereal species or cultivars in their effect on corn yield. To test this idea seven winter rye cultivars, two winter triticale cultivars, and three winter wheat cultivars were planted following soybean harvest in four years to determine their effect on the following corn crop. We found that the twelve cultivars differed in growth and nitrogen uptake over the four years. Additionally, the winter cover crops reduced corn yield in only two of the four years, but two winter rye cultivars had no effect on corn yield in either year. This research shows that there are differences in cover crop growth and their impact on yield of the following corn crop among winter cereal cultivars. In the future we may be able to select or breed for winter cereal cover crops that have a greater potential for shoot growth and also have a lower risk of negatively affecting corn yield. Reducing the risk of yield losses and increasing cover crop growth will increase adoption of cover crops, which will improve the sustainability of cropping systems.

Article Citation: Kaspar, T.C., and M.G. Bakker. 2015. Biomass production of 12 winter cereal cover crop cultivars and their effect on subsequent no-till corn yield. J. Soil Water Conserv. 70:353-364.

Journal of Soil and Water Conservation article here.


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