Interseeding Grass and Legume Cover Crops into Early Vegetative Stage Corn

Aug 2019


Three main areas of cover crop interseeding (cover crop species selection, establishment timing, and seeding method) need further research to understand how they interact with modern corn hybrids under Iowa climate and soil conditions. Further exploration of these factors will fill a knowledge gap to guide best management practices for interseeding cover crops into a corn cash crop.


This project will evaluate the effects of interseeded cover crop species, establishment timing and seeding method on corn productivity, to help help clarify treatment effects on:

  • cover crop establishment, biomass accumulation and nutrient uptake;
  • corn growth, productivity and nutrient uptake; and
  • weed community and diversity.


A comprehensive field study will be conducted at the ISU Northwest Research and Demonstration Farm, Sutherland, Iowa, and the Armstrong Research and Demonstration Farm, Lewis, Iowa. Three cover crop species will be used (winter rye, annual rye grass and red clover) with three establishment timings and two seeding methods (drilled or broadcast). Crop growth and development, nutrient uptake, crop reflectance and grain yield will be evaluated.

Researchers will conduct 5 to 10 on-farm trials using a subset of the treatments from the research farm trials that match farmers’ interests and farm suitability. The on-farm trials will compare no interseeding with 1 or 2 additional treatments in a replicated strip trial design throughout the field. Crop growth and grain yield will be evaluated.

Project Updates

Note: Project reports published on the INRC website are often revised from researchers' original reports to increase consistency.

December 2020

Research sites were harvested, and yields were attained (Armstrong, 15 Oct 2020; Castana, 20 Oct 2020 ; Sutherland, 14 Oct 2020). Trial average yield were Armstrong, 175 bushels/acre; Castana bushels/acre; and Sutherland, 227 bushels/acre. In general yields were 3-6 bushels/acre lower at the V5 seeding time compared to the V8 seeding time.

Cover crop biomass was determined in mid-July, early August, and near Nov 1. For mid-July, all species had emerged, however, the red clover was not large enough to get an accurate sample weight. For early August, the red clover was no longer present, but the other species were collected for biomass weight. Following harvest, at the Nov. 1 sampling date, there was not cover crop present to sample. In monthly observations, the cover crops established but as the season progressed growth and vigor diminished at all locations. This was likely due to drought conditions. Weed control was observed to be a huge factor. Weed control was superb at Sutherland and cover crop biomass was heavier compared to Armstrong where weed control was far from desired.

Six on-farm trials that successfully reached harvest for yield collection. One location, with Dordt College, used only annual ryegrass and was seeded at the corn V8 growth stage. The remaining five location used a cover crop mixture containing cereal rye, red clover, cowpea, and radish. Three were seeded at the corn V5 growth stage and two were seeded at the corn V8 growth stage. Across all on-farm locations, three locations had less than 2 bushels/acre difference between the no cover crop versus cover crop treatments, two had between 2 and 10 bushels/acre difference, and one had greater than 10 bushels per acre difference.

Outreach this period included presentations, for CropsTV and the Midwest Fish and Wildlife annual meeting.

July 2020

This project started in the spring of 2020 with timely corn planting at all locations. However, due to COVID-19, there have been some changes to treatments and field trials to ensure social distancing. For instance, there will not be a broadcast seeding treatment, and only the drill seeding treatment will be used at approximately the V5 and V8 corn growth stages at the research sites. Additionally, a third research site has been included which will have limited number of replications and data collection.

Research sites were planted at the research farms near Sutherland (9 and 18 June 2020), Castana (15 and 24 June 2020), and Atlantic (8 and 23 June 2020). Seed species used for the research sites were sole species of Elbon cereal rye, Freedom medium red clover, Iron and Clay cowpea, and RootMax annual ryegrass.

For on-farm locations, because of COVID-19, there will be five locations: four associated with ISU research farms and one associated with a farmer near Castana. The on-farm locations were seeded with a mix of Elbon cereal rye (24 lbs/acre), Freedom red clover (3.5 lbs/acre), Iron and Clay cowpea (17.5 lbs/acre), and Tapmaster daikon radish (3.5 lbs/acre).

Sutherland Research Farm - v5 seeding - now at v7. June 18, 2020. jpg

Corn stand counts were conducted at each research location. Crop reflectance, corn and cover crop biomass, and weed assessments have not been made because crop progression is not to the correct stage. Research trial visits and on-farm visual assessments for data collection are being planned. Quick observations made at the research farms indicate that the V5 cover crop interseeding emerged well because of nice rains following seeding plus a more open corn canopy. The red clover was a little slower to emerge. The V8 cover crop interseeding is presently emerged but does not look as good because of dryer weather and increased corn canopy. Further observations will be conducted in the coming weeks and at the end of the growing season.

Outreach included 1 field day.

December 2019

Field plot layouts have been developed and research farm managers are identifying plot space. Adjustments to the interseeder are being finalized and arrangement made for transporting to research and on-farm locations. A project meeting is being planned for early 2020 with the farm managers to begin the process of identifying on-farm locations and finalizing field plans for the growing season.