Planting Green Strategies for Maximizing Corn Emergence

Progress report for ONE19-339

Project Type: Partnership
Funds awarded in 2019: $29,526.00
Projected End Date: 09/30/2022
Grant Recipient: Pennsylvania State Extension
Region: Northeast
State: Pennsylvania
Project Leader:
Zachary Larson
Penn State Extension
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Project Information

Project Objectives:

This proposal seeks to determine if planting corn into standing, un-rolled cover crops negatively affects corn emergence and yield when compared to rolling cover crops prior to planting. Furthermore, it seeks to compare the use of row cleaners to create a bare soil strip around the seed slot versus rolling a cover crop adjacent to the seed slot, and its effects on corn emergence, slug damage and yield. The information gained from this proposal will be utilized to help farmers and educators quantify potential risks of planting into standing cover crops and will provide guidance in equipment setup for those wanting to adopt or refine planting green techniques.


The process of ‘planting green’ or planting a cash crop into a living, standing cover crop (figure 1) has become increasingly popular in the last 5 years.  Benefits of the practice include increased biomass production of the cover crop, reduced soil erosion and increased soil cover that provides habitat for beneficial organisms and buffers soil temperature fluctuations. (Reed, et al., 2019).

The implementation of the planting green concept varies widely among farmers. Early attempts included rolling with a cultipacker prior to planting or planting cash crops into standing covers without rolling. The practice evolved with the use of roller-crimpers to flatten cover crops prior to planting. More recently, rollers have been adapted to the planter frame (Dawn ZRX cover crop roller), combining two operations into one pass. This allows rollers to be mated to wider planters and avoids the need to modify tractors, which may be promising for widespread adoption of the practice.

While the roller-crimper has been an effective tool for planting into standing cover crops (figure 2), the enthusiasm and promotion of the practice has led to many farmers attempting to plant green without utilizing a roller-crimper, instead planting corn directly into tall, dense cover crops.  Much of this has occurred when planting green has been used as a ‘rescue’ when cover crops have not been terminated in a timely manner. Unfortunately, many farmers reported poor corn emergence when planting green into standing, un-rolled covers (figure 3) resulting in a negative opinion of the practice due to what may be poor execution of the concept.

Research on corn emergence demonstrates that when plants emerge at an uneven rate, they compete with each other, with late emerging plants showing reduced per-plant yields (Boomsma & Vyn, 2007). In addition, un- emerged plants result in lower stand populations which correlates with lower yields.  Factors that promote even emergence include consistent soil temperature and moisture in the seed zone and even light exposure to the seed row.  As important as these concepts are, they have not been widely documented in printed outreach materials or general discussions of the practice.

For planting green to continue as a popular and growing practice, there should be a greater understanding of how the practice affects corn emergence.  This includes demonstrating and quantifying the risks of planting into un- rolled cover crops and the benefits of rolling prior to planting. Therefore, an accurate side-by-side comparison of planting green into standing cover crops and its effects on corn emergence is needed to improve our body of knowledge and promote the successful implementation of the practice. Ultimately, a better understanding of how planting green management practices effect corn emergence will help farmers make better decisions when selecting cover crop species, modifying equipment for planting green and timing cover crop termination prior to planting.

Many studies have documented the effects of late emergence on corn yields. Early research demonstrated that plants emerging 7 and 14 days later than early emergers had yields approximately 2/3 and 1/2 of early emergers, respectively (Ford and Hicks, 1992).  Research in Ontario, Canada showed 4% and 8% stand yield reductions when one out of 6 plants was 2 and 4 leaf stages behind the remainder of the stand, respectively (Liu, et al., 2004).  A study of emergence in Oklahoma demonstrated that when one out of three plants in a stand emerged late, stand yields were reduced by 3 to 14% when plants emerged two days late and between 10 and 25% when plants emerged 5 days late (Lawless et al., 2012).  Observations at 9 locations in Virginia also showed a trend of decreasing per-plant yields for each day that late plants emerged behind the rest of the stand (VA Coop. Ext., 2016).

Multiple guidance documents outline the use of roller-crimpers for planting into standing, living cover crops, with much of the material focusing on cover crop selection and planting rates, timing of rolling and fertility management.  However, the effects on corn emergence are rarely noted. Information presented by Steve Groff (formerly presented by Cover Crop Solutions) advises against planting into cover crops greater than 12 inches tall and the PA No-till Alliance cautions against planting in to cover crops greater than 20 inches tall (PA No-Till Alliance, 2017).  In both cases data to support these claims is not provided.

At this time there is no known published research as to how planting green into un-rolled and rolled cover crops affects corn emergence.  However, Penn State Extension received reports of poor corn emergence in un-rolled cover crops in 2015 and 2016.  As a response, educators in the spring of 2017 recorded observations on corn planted into un-rolled cover crops, noting inconsistent emergence, reduced populations and plants having a tall and ‘spindly’ appearance relative to stands planted in rolled or bare fields or where machinery traffic flattened cover crops (Larson, 2018).

A series of observations were recorded in Somerset County, Pennsylvania in corn planted into a cereal rye cover crop.  Half of the field was rolled with a cultipacker and half was left un-rolled prior to planting. Plant populations and heights were recorded when plants were at the V5 to V6 leaf stage (table 1). While not structured as an experiment, analysis of the data as a completely randomized design, having lower statistical power than a randomized complete block, showed that corn planted into the un-rolled cover had lower emerged population (p<0.05), greater average plant height (p<0.10) and greater plant height deviation (p<0.01) compared to corn planted into the rolled cover crop. As noted in other reports, many of the corn plants attempting to grow through the un-rolled cover were taller but more spindly than those in the rolled cover.

In addition to a lack of published data of plant emergence in un-rolled covers, there is no documented information regarding the use of row cleaners on corn emergence when planting green. Early designs of planter-mounted roller crimpers utilized a disc-style row cleaner (figure 4), which creates a bare furrow approximately 6 inches wide around the seed slot.  However, in attempts achieve nearly 100% ground cover of the rolled cover crop, some farmers eliminated the row cleaner (figure 5), resulting in a rolled cover immediately adjacent to the seed slot.  In both cases there appears to be little data as to how the use or absence of row cleaners affects corn emergence when plating green.  Personal observations of full-with rollers (no row cleaners) suggests that closing the seed slot is more difficult and that there may be a greater risk from slug damage due to slugs entering the seed slot to consume germinated but not emerged corn plants. Conversely, those utilizing row cleaners claim they reduce slug damage by creating a “dead” zone between the dying cover crop and emerging corn in which slugs are less likely to cross and feed.


Boomsma, C. R., and Vyn., T. J.  2007.  Plant-to-Plant Uniformity is Essential for Optimum Yield in No-till Continuous Corn [Online].  Available at Purdue University, East LAyfayette, IN.

Ford, J. H., and Hicks, D. R.  1992.  Corn Growth and Yield in Uneven Emerging Stands. Journal of Production

Agriculture.  5:185-188.

Larson.  2018. Planting Green Impacts on Corn Emergence [Online]. Available at Pennsylvania State University, University Park, PA.

Lawless, K., Raun, W., Desta, K., and Freeman, K.  2012. Effect of Delayed Emergence on Corn Grain Yields. Journal of Plant Nutrition.  35:480-496.

Liu, W., Tollenaar, M., Stewart, G., and Deen., W.  2004. Impact of Planter Type, Planting Speed, and Tillage on

Stand Uniformity and Yield of Corn.  Agronomy Journal.  96:1668-1672.

Pennsylvania No-Till Alliance.  2017.  Planting Into Green Living Cover Crops [Online]. Available at

Reed, H., Karsten, H., Tooker, J., Curran, W. S., and Duiker, S. W. 2019. Planting Green 101: Penn State Research Summary [Online].  Available at summary.  Pennsylvania State University, University Park, PA.

Virginia Cooperative Extension.  2016.  2016 Virginia On-Farm Corn Test Plots [Online]. Available at Virginia Polytechnic and State University, Blacksburg, VA.


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Materials and methods:

In 2019, the field sites were seeded with cover crops in preparation for 2020 data collection.  Plots at the David Hernley (Bedford County, PA) farm were drilled with cereal rye (VNS) on September 19th at 47 lbs/ac.  Plots at the John Johnson farm (York County, PA) were drilled with cereal rye (VNS) at on November 30th at  90 lbs/ac.  The higher rate at the York site was utilized due to the much later planting date of the cover crop.

In 2020, the York County site hosted by John Johnson had to be dropped as Mr. Johnson suffered a heart attack over the winter and Dr. Reed and I felt that it was not appropriate to require Mr. Johnson to participate in the study during his recovery.  In place of Mr. Johnson's site, research was conducted at the Penn State Rock Springs Research Facility near State College, PA.

At the David Hernley Farm in Bedford, PA, research was conducted as planned.  The early termination plots were sprayed on 4/15 and planting occurred on 5/15.  Remaining standing cover crops were terminated on 5/21, however some rolled plots stood up due to wind.  The majority of planting measurements were taken on 6/17 at growth stage V/5, including population, plant height, and Greenseeker and lightbar readings.  Slugs were present at Bedford and slug damage ratings were taken.  The plots were sidedressed in late June and no other field activities occurred til harvest.  Fall activities included recording ear counts on 10/20 and harvesting plots on 11/20.

The data taken at the the Penn State Rock Springs Ag Research Station was piggybacked off of study carried out by Dr. John Wallace on herbicide programs in planting green scenarios.  The Aroostook rye cover crop was seeded on 10/1/19 at 90 lbs/ac.  Early termination plots were sprayed at late boot stage on 4/28, and the remaining cover crops were sprayed on 5/19.  Planting occurred on 5/19 and a sidedress nitrogen application was performed on 6/29.  Measurements of plant height and population and Greenseeker and lightbar readings were taken on 6/19 at stage V5.  There was no observable slug damage at the Rock Springs site.  Exclusive to the Rock Springs site, plant height measurements were also taken at tassel (VT) on 6/27.  Ear counts were recorded on 10/7 and plots were harvested on 10/11.

The field site for the 2021 Bedford County trial was seeded on 9/17 at 45 lbs/ac, however due to extremely dry conditions throughout the summer and fall emergence was very uneven.  Thin spots in the stand were seeded on 11/21 with wheat at 75 lbs/ac.  At this point, it is unknown how variable plots will be in 2021 or if treatments can be positioned in areas of heavy rye growth.

The field site for the 2021 York County trial was seeded with cereal rye at 95 lbs/ac on 11/10.

At the David Hernley Farm in Bedford, PA, 2021 research methods closely followed those form 2020.  However, 2021 plots were smaller as poor cover crop establishment forced the exclusion of some of the study area.  The early termination plots were sprayed on 4/22 and planting occurred on 5/21.  Corn population and emergence measurements were taken on 6/14-15, growth stage V4 including population, plant height, and Greenseeker and lightbar readings.  Slugs were again present and slug damage ratings were recorded.  A second Greenseeker measurement was take on 6/24 at growth stage V6.  Ear counts were recorded on 11/2 and plots were harvested on 12/1.

Research was also performed at a second cooperator location in Adam County with Matt Kehr.  However, the available equipment was such that an un-rolled treatment could not be implemented, with the site having early burndown, rolled-row cleaners and rolled-no row cleaners treatments.  Cover crop early termination was performed on 6/5 and planting occurred on 6/17.  Measurements of plant height and population and Greenseeker readings were taken on  7/7 at stage V4.  Second Greenseeker readings were taken on 7/15.  Late season ear counts were performed on 10/22 with harvest occurring in November 2021.

Similar to 2020, the 2021 Rock Springs research was performed on a site also hosting an herbicide study performed by Dr. John Wallace.   Early termination plots were sprayed at late boot stage on 4/30 and planting occurred on 5/16.  Measurements of plant height and population and Greenseeker readings were taken on 6/18 at stage V5.  There was no observable slug damage at the Rock Springs site.  Second Greenseeker measurements were taken at V7 on 6/29.  Ear counts were recorded on 10/21 and harvest occurred in November 2021.

Research results and discussion:

A slight change in the experiment design occurred prior to 2020.  The initial design called for a split plot design with two main plots (rolling, no roll) and 2 split plots (row cleaners up, row cleaners down) for a total of four treatments roll-row cleaners, roll-no row cleaners, no roll-row cleaners, no roll-no row cleaners.  This initial design did not include an early burndown control plot and due to the setup of the planter it was infeasible to operate with the roller up but the row cleaners down.  Therefore the design was changed to a randomized complete block with the following treatments:  early burndown, roll-no row cleaners, roll-row cleaners, no roll.  Ultimately, we thought that this was a better option as the study would include a burndown that represents typical PA cover crop termination practices.  Additionally, we believed that there would be little observable difference between the row cleaner subplots in the no roll treatment and that four separate treatments would provide more meaningful data for the experiment. 

Planting of the Bedford PA plots proved to be challenging in obtaining the desired condition for each treatment due to a few issues.  First, the row cleaner in the Dawn ZRX setup is such that it moves up and down with the cover crop rollers.  The row cleaner depth of cut can be adjusted relative to the roller by turning a threaded rod, however at the highest position the row cleaner still dug into the ground when planting on slopes or bumps as the tollbar of the planter pitched down relative to the tractor.  This resulted in places in the rolled-no row cleaner treatment where there was in fact row cleaning.  Plant population and height measurements were taken in areas where the desired rolled but tight to the seed slot condition was present, however yield measurements will capture all conditions across the treatment.  Additionally, high winds after planting combined with a later than desired post-plating cover crop termination blew some of the rolled cover back up, creating a low standing cover condition in some places and covering the row in the rolled-row cleaner treatment.  Like with the planting issues noted above, plant height and population measurements were taken when the desired treatment condition was present, with those issues possibly affecting plot yields.

Learning from the Bedford issues, a different strategy was implemented at Rock Springs.  In place of raising and lowering the row cleaners between treatments to obtain a rolled-row cleaners and rolled-no row cleaners treatment, an I&J 10 ft. cover crop roller was front mounted to the planting tractor to eliminate issues with incidental row cleaning on the rolled-no row cleaners treatment resulting in the following planter treatments: early burndown (ZRX rollers down to engage row cleaners), no roll (ZRX rollers and row cleaners raised), roll-row cleaners (ZRX rollers down and row cleaners down), roll-no row cleaners (I&J row roller down, ZRX rollers up).  This better resulted in the four desired, post planting conditions:  early burndown with row cleaning, tall standing cover, rolled cover crop with cover tight to seed slot, and rolled cover crop with a cleaned "dead zone" adjacent to the seed slot.  This methodology will be used for all 2021 locations.

Another issue encountered in implementing the experiment methodology is excessive cover rolling in the no roll treatments.  When a 4 row planter is utilized, wheel traffic from the tractor and planter rolls a substantial amount of the cover in the no roll treatments, leaving 1-2 rows that have standing cover on each side of the seed slot.  Plant population and height data was effectively recorded from those areas, but the rolling of a portion of the crop may mask yield differences that would otherwise be expressed if a wider planter was used and a larger percent of the no roll treatment was left undisturbed.

Significant differences (α=0.1) existed between treatments for multiple measurements in 2020 at the Bedford site, while no significant differences were identified for at the Rock Springs location.  A possible reason for the difference is that the Rock Springs Location had lower levels of rolled biomass compared to the Bedford site.  As hypothesized, height of corn plants at V5 was higher for those in the un-rolled cover, with plants being on average 3.3 and 6.4 inches taller than those in the rolled row-cleaner and early burndown treatments, respectively.  Plant height standard deviation was higher in the un-rolled cover as well, approximately 2 inches greater than the deviation found in the early burndown treatment.  Physical differences between the plants were present as well, with those in the un-rolled cover having a much longer, but narrower leaf surface with less plant rigidity, resulting in a more "spindly" appearance.  It appears that the plants are dedicating all carbohydrate reserves to putting on plant height to escape the shading of the cover, at the possible expense of stalk and root development.

In addition to height differences, plants in the un-rolled area experienced greater slug damage on average, with visual ratings of damage double that of all other treatments a the Bedford location in 2020.  Plant NDVI readings, as recorded with the Greenseeker, were significantly lower in the no roll treatment, when compared to the early burndown and rolled with row cleaners treatment.  The number of harvestable ears pear acre in the un-rolled treatment was significantly lower than that of the early burndown treatment as well, with the early burndown having over 3,000 more ears per acre at harvest.  Interestingly, the ratio of harvestable ears per acre to the V5 plant population was between 0.97 to 0.99 for the early burndown, rolled-row cleaners and rolled-no row cleaners, while for the un-rolled treatment the ratio was 0.91.  This suggests that a higher rate of plant mortality or reduced ear development occurred in the un-rolled cover.  There was no difference in yield between treatments at the Bedford and Rock Springs locations.

Data analysis is currently underway for all 2021 locations and the project as a whole.  Conditions in 2021 at the Bedford site were similar to those in 2021 in terms of cover crop biomass and planting timing.  However, a different planter had to be used for 2021.  Unfortunately the planter was lighter compared to the one used in 2020, making it difficult to transfer enough weight to the rollers and row units in some spots.  However, emergence looked good despite what may have been slightly shallower planting depth.  The conditions at Rock Springs were much more challenging, with an extremely heavy, lodged cover crop present at planting.  For the Rock Springs location a newly upgraded planter, equipped with many Precision Ag components, was used for 2021.  Unfortunately, the high biomass cover lifted the row units such that adequate planting depth could not be achieved, and the planter sensing the shallow depth shut off the row units, drastically altering as-planted populations.  However, this issues can be easily identified in the field as all four rows shut off at the same time, so measurements were not taken in those areas.  Final yield measurements will be based on plant populations as recorded by the precision system.  The conditions at the Adams County site were typical for the area and consistent across the study.

As of January 2022, only data from the Bedford site has been analyzed.  Again, significant differences (α=0.1) existed between treatments for multiple measurements in 2020 at the Bedford site.  Unlike 2020, differences in V4 population were present, with the no roll and rolled-no row cleaner having lower populations than the early burndown and rolled-row cleaner treatments.  There were no differences in plant height in 2021, although taking measurements one growth stage earlier may have affected those results.  Similar to 2020, plant height standard deviations were present, with the no-roll treatment having significantly higher plant height deviations.  Additionally, plant NDVI readings, were significantly lower in the no roll treatment, when compared to the early burndown and rolled-row cleaners treatment.  Slug damage patters were also similar in 2021, with the un-rolled treatment showing significantly higher slug damage, on average.



Participation Summary
2 Farmers participating in research

Education & Outreach Activities and Participation Summary

6 Consultations
1 Tours
2 Webinars / talks / presentations

Participation Summary:

31 Farmers participated
31 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

In the summer of 2020, Penn State Extension held a virtual agronomy webinar series, with participants roughly split between farmers and crop consultants.  On 8/14 I spoke at a session focusing on planting green.  While no data was discussed, I reviewed the concepts of which this work as based and shared progress pictures from the Rock Springs and Bedford sites, with initial impressions of field conditions.

Initial results were presented by Zachary Larson in October 2021 at the Keystone Crops and Soils Conference in Grantville PA to an audience of crop consultants.  This included a review of all 2020 results, reviewed on a per-location basis and 2021 data recorded up to September.

Plans were in place to present the data at the Western PA Soil Health Conference in Latrobe, PA in January 2022, however, the event was cancelled.  The results of the project will also be presented by Heidi Reed at the Lebanon Crops Day in Lebanon, PA.

Data from the study will be used for a Penn State Field Crop News article, where the plant height, population and NDVI data will highlight some misconceptions of cover crop as they relate to alleopathy.

Learning Outcomes

12 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

At the Keystone Crops and Soils Conference approximately 8 crop advisers were involved in a follow-up discussion of planting green, whereby the results were discussed along with personal experiences.  The presented data confirmed to the group that rolling should occur when planting corn to prevent issues with low plant populations, variable plant populations and yield loss.

During the summer of 2021, two farmers interested in planting green from Blair County, PA were given a tour of the Bedford site.  There we observed the differences in treatments and discussed Mr. Hernley's experiences with planting green.  The two Blair farmers had intentions to plant green without rolling the cover, but after seeing the difference first-hand, decided that they should purchase cover crop rollers before attempting the practice.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.