Field-Scale Evaluation of Corn Response to Nitrogen Fertilizer Application Timing following a Rye Cover Crop

Final report for GNC22-355

Project Type: Graduate Student
Funds awarded in 2022: $14,740.00
Projected End Date: 12/31/2023
Grant Recipient: Purdue University
Region: North Central
State: Indiana
Graduate Student:
Faculty Advisor:
Dr. Daniel Quinn
Purdue University
Faculty Advisor:
Dr. Shalamar Armstrong
Purdue University
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Project Information


Previous research has documented rye cover crop (RCC) benefits on weed suppression, erosion control, water quality improvement, and organic matter contributions. Yet, RCC adoption is often low prior to corn, suggesting further research and extension needs to be conducted to develop and disseminate corn management recommendations following a RCC. Therefore, the proposed objective of this study is to evaluate corn growth, yield, and nutrient uptake responses to different N fertilizer application timings following a RCC using multiple field-scale research environments. The outcomes of this study include: development of corn N fertilizer timing recommendations following a RCC, development of resources to train and disseminate educational information to farmers and crop consultants across the North Central SARE region, and reduced RCC hesitancy prior to corn. The treatments within this study include: RCC and no cover crop and N fertilizer applied at a rate of 44 kg N ha-1 in a 2 inches to the side, 2 inches below the seed (2x2) starter at planting + remaining N fertilizer sidedressed at the V5 growth stage, a 2x2 starter + remaining N fertilizer sidedressed between the corn rows at the V10 growth stage, and a 2x2 starter + V5 sidedress + V10 sidedress. This study will be conducted across entire farm fields using commercial equipment at three locations across Indiana to enhance result applicability to North Central region farmers. Data collection will include: soil N analysis throughout the corn growing season, RCC total biomass, carbon and N analysis, corn stand assessment, corn plant biomass and N uptake analysis at growth stages R1 and R6, and corn ear samples for grain yield component examination. Furthermore, NDVI imagery will be collected every two weeks using an unmanned aerial vehicle (UAV) to assess spatial plant responses regarding treatment applications. By developing N fertilizer timing recommendations following a RCC, farmers will be able to adopt more efficient fertilizer management practices, optimize corn production following a RCC and be more likely to implement RCC prior to corn planting. Results from this study will provide direct, applicable information to North Central SARE region farmers to reduce corn yield losses following a RCC, RCC hesitancy, and allow a RCC to be implemented consecutively in farmers cropping rotations.

Project Objectives:

Since 2012, cover crop use in the Midwest prior to corn production has been steadily increasing. However, adoption often remains low compared to total corn production acres. Low adoption is often driven by a lack of knowledge regarding proper agronomic management of corn within a cover crop system and producer hesitancy caused by reduced crop yields. Rye cover crop use is popular and is often the only cover crop choice for farmers due to germination success, biomass production, and survival. A RCC can provide environmental benefits such as reduced soil erosion, scavenging of excess N, and suppression of weeds. However, limited knowledge has been gathered on proper agronomic management techniques specific to corn following a RCC. Developing knowledge and skills on appropriate agronomic management of corn following a RCC could help change the attitude of RCC hesitant farmers and lead to an increased adoption of this sustainable practice. Therefore, the outcomes of this study are to identify N fertilizer application timing methods on a field scale using commercial farm equipment that will help reduce corn N stress and yield loss following a RCC. In addition, educational and extension materials will be developed and presented to help train, improve overall knowledge, and influence producer behavior. Behavioral changes will be tracked using extension meeting and field training surveys and scheduled consultations with a farmer advisory committee. The accomplishment of our outcomes will help educate farmers, certified crop advisors, government agency officers, and agricultural professionals in the North-Central Region and reduce RCC hesitancy.


Materials and methods:

Field-scale research trials were conducted at three locations in Indiana over 2022 and 2023, namely the Purdue Agriculture Center for Research and Education (ACRE) in West Lafayette, Southeast Purdue Agricultural Center (SEPAC) in Jennings County, and Davis Purdue Agricultural Center (DPAC) in Randolph County. These trials aimed to study the impact of rye cover crops (RCC) and nitrogen (N) fertilizer application timing on corn production. All locations utilized no-till practices, rainfed conditions, and followed a corn-soybean rotation. 

Experimental procedures involved a factorial, randomized complete block design with varying replications across locations. RCC treatments included fall drill-seeding at 50 kg/ha or no rye cover crop. Nitrogen fertilizer application timings each included a 5 cm to the side and 5 cm below starter fertilizer application at planting at a rate of 44 kg N/ha with remaining N fertilizer appled at V5 sidedress, V10 sidedress, or V5+V10 sidedress. Corn hybrids were planted at university recommended seeding rates based on location, and treatments were applied using commercial farm equipment.

Data collection included pre-plant composite soil sampling, pre-RCC termination soil inorganic N sampling, RCC biomass assessment, evaluation of corn plant stands, measurement of corn biomass and nitrogen content, and analysis of corn grain yield and yield components. Statistical analysis was performed using ANOVA with linear mixed-effect models, considering factors such as RCC, N timing, location, and year. Data were analyzed separately for each site-year due to significant interactions with treatments.

Overall, the research aimed to understand how RCC and N fertilizer application timing influence corn production under different environmental conditions in Indiana.

Research results and discussion:


Shoot Biomass and Nitrogen Uptake of Rye Cover Crop

Throughout the site-years, the RCC C/N ratio averaged 12.5 (ranging from 11 to 14), 21 (ranging from 18 to 24), and 26.5 (ranging from 24 to 29) at ACRE, DPAC, and SEPAC, respectively, with an overall average C/N ratio of 20:1 (see Table 1). The total C uptake in RCC shoots averaged 584.99 (ranging from 577.12 to 592.85), 348.14 (ranging from 189.77 to 506.51), and 692.54 (ranging from 518.94 to 866.13) kg C/ha at ACRE, DPAC, and SEPAC, respectively, with an average C uptake of 541.89 kg C/ha across the site-years. Total RCC aboveground N uptake averaged 47.39 (ranging from 43.41 to 51.37), 15.58 (ranging from 10.24 to 20.91), and 25.96 (ranging from 22.23 to 29.68) kg N/ha at ACRE, DPAC, and SEPAC, respectively, with an average N uptake of 29.64 kg N/ha across the site-years. The total biomass for RCC shoots averaged 1395.49 (ranging from 1391.33 to 1399.65), 821.2 (ranging from 456.08 to 1186.32), and 1636.1 (ranging from 1267.64 to 2004.47) kg/ha at ACRE, DPAC, and SEPAC, respectively, with an average biomass of 1284.25 kg/ha across the site-years. Planting dates ranged from October 5 to November 16, and RCC termination dates ranged from April 13 to May 22 across the site-years. Due to delayed RCC planting dates at DPAC and late cash crop harvest, RCC produced the lowest biomass at this location in 2022 and 2023.

Table 1. Planting date, termination date, mean aboveground biomass, total carbon (C), total nitrogen (N), and C/N ratio of RCC samples taken prior to termination at individual site-years. ACRE, DPAC, and SEPAC, IN (2022-23).



Planting Date



Total Biomass

Total C

Total N

C/N Ratio





Kg ha-1

Kg ha-1

Kg ha-1




Oct 21

Apr 27







Oct 20

Apr 19







Nov 16

May 15







Nov 2

May 22







Oct 10

Apr 24







Oct 5

Apr 13






Soil NH4-N and NO3-N:

Before RCC termination, soil NH4-N was notably decreased by the presence of RCC in 2 out of 6 site years compared to when no RCC was present (refer to Table 2). Additionally, soil NO3-N was diminished in 5 out of 6 site years when RCC was present, compared to situations without RCC. In instances where RCC was absent, soil NO3-N levels prior to RCC termination averaged 11.9 mg/kg across all site years; however, with RCC present, soil NO3-N averaged 8.1 mg/kg. Overall, the findings consistently show reductions in spring soil NO3-N (0-30 cm depth) before RCC termination across various locations and conditions.


Table 2.  Mean soil NH4-N and NO3-N (0-30 cm) in response to RCC presence sampled one day prior to RCC termination. ACRE, DPAC, and SEPAC (2022-23).



Cover Crop

Soil NH4-N

Soil NO3-N




mg kg-1

mg kg-1





10.31 a*

6.69 b

28.6 a

19.6 b





3.31 a

3.72 a

11.25 a

5.25 b





5.31 a

4.41 a

9.28 a

7.62 b





4.09 a

2.88 a

6.75 a

3.84 b





2.89 a

2.61 a

7.06 a

6.94 a





6.61 a

4.78 b

8.50 a

5.72 b

* Mean soil NH4-N and NO3-N values within each location and year that do not contain the same lowercase letter are determined significantly different from each other (P<0.1)


Grain Yield:

Across different N fertilizer application timings, RCC led to a decrease in corn yield compared to no cover crop in 5 out of 6 site-years, averaging a reduction of 7% (15709 kg ha-1 vs 14606 kg ha-1). However, despite the yield decreases caused by RCC, a significant interaction between N timing and RCC presence was noted in 5 out of 6 site-years, indicating that optimal N timing varies with the presence of RCC (refer to Figures 1 and 2). In the absence of RCC, using a 5x5 + V10 or 5x5 + V5 + V10 N application resulted in yield reductions in 4 out of 6 and 0 out of 6 site-years, respectively, compared to a 5x5 + V5 N application. Conversely, with RCC, the use of a 5x5 + V10 or 5x5 + V5 + V10 N application led to yield decreases in 6 out of 6 and 2 out of 6 site-years, respectively, compared to a 5x5 + V5 N application. Overall, there were more instances of corn yield reductions due to delayed N fertilizer application observed across study site-years when RCC was present compared to when RCC was absent.


Figure 1. Corn grain yield (kg/ha) in response to rye cover crop (RCC) presence and nitrogen (N) fertilizer application timing. ACRE, DPAC, SEPAC (2022). Individual box plots within each location that do not contain the same letter are determined significantly different from each other (P<0.1).


Figure 2. Corn grain yield (kg/ha) in response to rye cover crop (RCC) presence and nitrogen (N) fertilizer application timing. ACRE, DPAC, SEPAC (2023). Individual box plots within each location that do not contain the same letter are determined significantly different from each other (P<0.1).



The aim of this study was to investigate the impact of in-season nitrogen (N) fertilizer management on alleviating corn N stress following a rye cover crop (RCC) and determining the best timing of in-season N fertilizer applications for corn grown after a RCC. This research addresses gaps in understanding essential agronomic decisions to enhance corn yield after a RCC with in-season N fertilizer management. Overall, the findings suggest that applying a 5x5 starter application alongside a V5-only sidedress N application led to improved corn yield, yield components, and plant N uptake after a RCC compared to using a V10-only or V5 + V10 in-season N application. Moreover, delayed in-season N fertilizer application is more likely to induce N stress and yield reduction in corn following a RCC than in corn not following a RCC.

Rye cover crop biomass levels, planting dates, and termination dates varied across different site-years. Biomass was limited at the DPAC location in 2022 and 2023 due to delayed fall planting, although in 2023, biomass likely increased until termination. Earlier RCC planting after cash-crop harvest resulted in longer RCC growth periods and higher biomass production at other locations, consistent with previous research. RCCs prior to corn planting can lead to a soil surface environment with significantly more carbon (C) than nitrogen (N), potentially causing N immobilization if the shoot residue's C/N ratio exceeds 25:1. Soil NO3-N levels were reduced when following a RCC compared to no RCC in most site-years, indicating a decrease in early-season N availability for corn.

The V5 nitrogen timing was found to be the most effective treatment in reducing corn N stress and yield loss after a RCC. Combining a 5x5 starter N application with the remaining N at V5 allowed for earlier N availability and mitigated the potential yield-reducing effects of a RCC. Applying the majority of N earlier (e.g., pre-plant) was ineffective compared to split-applied N. Delaying N application until V10 without a RCC reduced yields, emphasizing the importance of timely N application. When not following a RCC, the inclusion of a V10-only N application did not reduce yields compared to the V5 timing. Overall, the majority of observed corn stress and yield reductions from the RCC were attributed to soil and plant N differences, highlighting the necessity of a 5x5 + V5 N application when corn follows a RCC.


This research aimed to determine the optimal in-season N application timing to reduce corn N stress and improve corn yield following a RCC. The findings underscore the challenges faced when corn follows a RCC, including reduced spring N availability due to RCC N uptake and N immobilization. However, the study highlights the importance of using a 5x5 + V5 N application to mitigate corn N stress and yield loss following a RCC. Farmers are advised to avoid delayed in-season N applications (e.g., V10 or V5 + V10) when following a RCC. While delayed in-season N application may be tolerated when not following a RCC, it rarely provides additional benefits beyond a V5-only in-season N fertilizer application.

Participation Summary
3 Farmers participating in research

Educational & Outreach Activities

15 Consultations
5 Curricula, factsheets or educational tools
6 On-farm demonstrations
4 Online trainings
5 Published press articles, newsletters
15 Webinars / talks / presentations
6 Workshop field days

Participation Summary:

1,700 Farmers participated
2,100 Ag professionals participated
Education/outreach description:

This research was presented at extension events in 2 countries (U.S. and Canada) and 4 states (Missouri, Indiana, Maryland, Ohio) to 3,000+ farmers, researchers, conservationists, and agricultural professionals over the project period. The research was presented through conferences, on-farm meetings, field days, and workshops. In addition, results were showcased through interviews and newsletter articles for Indiana Prairie Farmer, Purdue Pest and Crop Newsletter, Indiana Corn and Soybean Post, and the Purdue Crop Chat Podcast, each of which reach 25,000+ farmers and agricultural professionals. These results will also be published in a peer-reviewed journal article which is currently in progress. 

Project Outcomes

Project outcomes:

This research was presented at extension events in 2 countries (U.S. and Canada) and 4 states (Missouri, Indiana, Maryland, Ohio) to 3,000+ farmers, researchers, conservationists, and agricultural professionals over the project period. This research provides direct applicable information to help inform farm management practices when following a rye cover crop. The inclusion of a rye cover crop prior to corn establishment can have detrimental impacts to corn which include nitrogen stress and yield loss and this project helps to address these issues through further understanding how nitrogen fertilizer should be applied in-season to corn following rye. This project further allows farmers to adopt a rye cover crop prior to corn which can improve environmental and social benefits for farmers through improved water quality, soil erosion reductions, and herbicide resistant weed control. Furthermore, this project helps maintain corn yields and become more efficient with nitrogen fertilizer following a rye cover crop rather than increasing the total nitrogen rate, which has direct economic benefits. 

Knowledge Gained:

Knowledge gained included improved understanding of how to manage in-season nitrogen fertilizer applications in corn following a rye cover crop. Our research showcased the importance of timely nitrogen fertilizer applications in corn following rye and the detriment if nitrogen was applied too late, especially when following rye. Overall, our research gained additional knowledge in managing corn following a rye cover crop and making sure that grain yield losses and nitrogen stress are not observed. 

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.