Final report for GNC18-261
Project Information
Despite numerous environmental benefits associated with cover crops including reducing erosion, improving infiltration, mitigating nutrient loading in surface waters, and improving soil health (Kaspar et al 2001, Kaspar and Singer 2011, Schnepf and Cox 2006), many farmers are reluctant to include cover crops in their production systems because of reported yield declines, especially in corn. There are numerous potential reasons for this yield decline, including seedling disease that reduces stand, and seedling vigor that leads to uneven stands. Cover crops, especially grass cover crops, are hosts of the same pathogens that infect corn seedlings (Bakker et al 2016). Cover crops serve as a 'green bridge' for pathogens by maintaining pathogen populations over the winter between harvest and planting of cash crops, which is normally when pathogen numbers decline on non cover crop fields (Smiley et al 1992; Acharya et al 2017). The goal of this project was to understand the effects of a winter rye cover crop on corn disease, growth and development, specifically how distance from decomposing rye affect corn.
To accomplish this we collaborated with the Iowa Soybean Association On-Farm Network who identified two farmers for us to work with over two years. A cover crop of winter rye was seeded in either 30-inch and 15-inch, or 30-inch and 7-inch rows. The corn was planted in 30-inch rows and thus was 15 inches, 7.5 inches, or 3.5 inches from the decomposing winter rye. Both fields were no-till corn-soybean rotations with four replications. At both farms no effect of distance from winter rye treatments were detected on corn growth including yield. At one farm an effect of distance from winter rye was detected on radicle root rot in both years (2019, P = 0.0514; 2020, P = 0.0016). Radicle root rot was reduced when corn was planted further away from winter rye.
The results of our project were shared at the Department of Plant Pathology and Microbiology weekly seminar (https://www.youtube.com/watch?v=gkO2BHenNhc) and an ICM Blog (https://crops.extension.iastate.edu/blog/alison-robertson-sarah-kurtz/can-corn-benefit-social-distancing). Post on social media (Twitter and Facebook) linking to these outputs were done to share the research. Our outreach and output efforts will be evaluated by means of social media, number of citations and surveys over the next year. This project will increase the profitability of farmers by reducing the risk of yield reductions in corn while improving the soil and water quality, and providing a best management practice for farmers.
References:
Acharya, J., Bakker, M. G., Moorman, T. B., Kaspar, T. C., Lenssen, A. W., & Robertson, A. E. 2017. Time interval between cover crop termination and planting influences corn seedling disease, plant growth, and yield. Plant Dis. 101:591–600. https://doi.org/10.1094/PDIS-07-16-0975-RE
Bakker, M. G., Acharya, J., Moorman, T. B., Robertson, A. E., & Kaspar, T. C. 2016. The potential for cereal rye cover crops to host corn seedling pathogens. Phytopathology, 106: 591-601.
Kaspar, T. C., Radke, J. K., and Laflen, J. M. 2001. Small grain cover crops and wheel traffic effects on infiltration, runoff, and erosion. J. Soil Water Conserv. 56:160-164.
Kaspar, T.C., and J.W. Singer. 2011. The use of cover crops to manage soil. In Soil Management: Building a Stable Base for Agriculture, eds. J.L. Hatfield and T.J. Sauer, 321-337. Madison, WI: American Society of Agronomy and Soil Science Society of America.
Schnepf, M., and C. Cox, eds. 2006. Environmental Benefits of Conservation on Cropland: The Status of Our Knowledge. Ankeny, Iowa: Soil and Water Conservation Society
Smiley, R. W., Ogg, A. G., & James Cook, R. 1992. Influence of glyphosate on Rhizoctonia root rot, growth, and yield of barley. Plant Dis. 76:937-942.
The objectives of our proposal were to: (i) understand the impact of spatial planting arrangement of winter rye CC on corn seedling disease, growth, and development, and (ii) determine the Pythium spp. population density in the soil spatially.
To address our objectives we collaborated with the Iowa Soybean Association On-Farm Network who identified two farmers for us to work with over two years. Both fields were no-till corn-soybean rotations with four replications. One farmer seeded the winter rye cover crop on 30-inch rows and 15-inch rows. The second farmer seeded the winter rye cover crop on 30-inch rows and 7-inch rows and terminated the winter rye early or late. Corn was planted on 30-inch rows resulting in the corn being 15-inches, 7.5 inches or 3.5 inches from the decomposing rye.
Cooperators
Research
In general, the distance between a pathogen and host influences the risk of pathogen infection (Real and McElhany 1996). We wondered if physically separating a pathogen from a host may reduce the chance of host infection.
Recently, a small number of farmers have used their cash crop planting machinery to seed winter rye in 30-inch rows (Theo Gunther personal communication). In the Midwest corn and soybean are usually planted in 30-inch rows. As precision planting becomes more common on Iowa farms, it is possible farmers could seed a winter rye CC in the interrows to physically separate the winter rye CC from the corn rows planted the following season. It is possible this physical separation could reduce the impact of a winter rye CC on corn seedling disease and corn yield while continuing to provide environmental and soil health benefits.
Trials were established on two farmer fields. Both fields were in a corn-soybean rotation and winter rye was planted after soybean harvest. Each grower had slightly different treatments. In 2019 and 2020, Grower 1 had three treatments; 15-inch drilled winter rye, 30-inch drilled winter rye, and a no winter rye control planted in strips across the field. Winter rye was sprayed with glyphosate three days before corn was planted. Data was collected from four replications of each treatment strip. In 2019, Grower 2 had five treatments; (1) early terminated winter rye drilled in 7-inch rows, (2) early terminated winter rye drilled in 30-inch rows, (3) late terminated winter rye drilled in 7-inch rows, (4) late terminated winter rye drilled in 30-inch rows, and (5) no winter rye control planted in strips across the field. Early terminated winter rye was sprayed with glyphosate four days before planting and late terminated winter rye was sprayed with glyphosate five days after corn was planted. Data was collected from eight replications. In both fields, corn was no-till planted in 30-inch rows.
In both grower's fields, in each treatment strip there were two designated plots that were two-rows wide by 50 ft long. Grower 1's field was sampled around corn growth stage V2-V3 in both years. This growth stage is ideal for identifying seedling root rot. Grower 2's field was sampled around corn growth stage V4-V6 due to weather and wet field conditions in 2019.
In each plot stand counts were taken, ten corn plants were collected, and two soil samples were taken with a soil probe; one in the corn row and one in the interrow. Corn plants were washed and shoot length, shoot dry weight, and growth stage measurements were taken. These growth parameters are important for learning about corn growth and development. Root rot severity was rated as the percentage of both radicle and seminal roots that were rotted. A small portion of radicle roots from each plot were sampled for DNA extraction using a plant DNA extraction kit. A small portion of soil from each soil sample were used for DNA extraction using a soil DNA extraction kit. DNA samples were processed using qPCR to quantify Pythium Clade B population numbers. These data were used to compare Pythium populations among treatments.
Around corn growth stage R6, stand counts and barren plants were recorded in Grower 1's field in both years. These data were not taken in Grower 2's field due to time constraints. Yield data were collected at harvest for both growers. Yield data for Grower 2's field was only collected for three replications due to different corn varieties and harvest dates.
Analysis of variance (ANOVA) was performed on data for all measured parameters using PROC GLIMMX in SAS (version 9.4). Winter rye seeding method was treated as a fixed factor and replication as a random factor. Since treatments varied between the two on-farm studies, data were analyzed separately for each on-farm study. The interactions between year and treatments were significant for some parameters for Grower 1; therefore, results were analyzed separately for each year. Data for pathogen quantification were not normally distributed therefore, data were square root transformed. If treatment effects were detected at 0.10 level of significance in the ANOVA, then treatment means were compared using Fisher’s least significant difference at P = 0.10.
References:
Real, L. A., and McElhany, P. 1996. Spatial Pattern and Process in Plant‐Pathogen Interactions. Ecology, 77:1011-1025.
Treatment effects were not detected for most data collected for Grower 1's fields (Table 1, 2, and 3). However, there was a difference among treatments for radicle rot severity (2019, P = 0.0514; 2020, P = 0.0016; Table 1). As suspected, corn planted into 15-inch winter rye had higher radicle rot severity than corn planted into 30-inch winter rye and no winter rye. Pythium clade B populations did not differ between soil in the corn row and interrow (2019, P = 0.6145; 2020, P = 0.4189; Table 2).
Similarly, in Grower 2's field, the effects of winter rye spacing and termination date treatments on most growth parameters of corn were not significant. Treatment effects were detected for shoot length (p=0.0121; Table 2). Corn shoots were taller when corn was planted into no winter rye compared to corn planted into the winter rye treatments. There were no differences among treatments for radicle and seminal rot severity (P = 0.2132; P = 0.6195, respectively; Table 4). Pythium clade B populations detected in the soil were low.
There are several reports that a winter rye CC did not negatively affect corn yield (Andraski and Bundy 2005; Ball et al. 2005; Doran and Smith 1991; and Snapp and Surapur 2018). Thus, the negative effect of a winter rye CC on corn does not occur in all fields or years. It is unknown whether there was a history of seedling disease in the fields we used for our study. Additional research at more locations over more growing seasons is needed to fully understand the factors that play a role in reducing corn yield after a winter rye CC.
Table 1. Average effects of winter rye cover crop treatments on corn seedling root rot, density of Pythium spp. belonging to clade B in radicles, and growth parameters of corn at growth stage V2 to V4 in Grower 1's field.u
| Year | Treatments | Shoot height (cm)v | Shoot dry weight (g)w | Growth stage | Radicle rot severity %x | Seminal rot severity %y | Radicle clade B (copies) |
| 2019 | |||||||
| 15-inch rye | 27.8 | 3.4 | 3.3 | 9.7 az | 5.6 | 21.1 | |
| 30-inch rye | 28.8 | 3.7 | 3.3 | 3.1 b | 5.1 | 24.8 | |
| No rye | 27.9 | 3.4 | 3.4 | 7.1 ab | 6.1 | 25.8 | |
| P > F | 0.4189 | 0.6838 | 0.8376 | 0.0514 | 0.7145 | 0.8594 | |
| 2020 | |||||||
| 15-inch rye | 31.1 | 5.1 | 2.9 ab | 25.3 a | 5.5 a | 99.8 a | |
| 30-inch rye | 32.4 | 5.3 | 3.0 a | 11.7 b | 2.2 b | 68.1 ab | |
| No rye | 31.3 | 5.1 | 2.8 b | 11.8 b | 2.9 b | 40.8 b | |
| P > F | 0.28 | 0.7543 | 0.1453 | 0.0016 | 0.0758 | 0.2128 | |
u Density is expressed as target pathogen ITS gene copies per synthesized DNA, and is reported as copy number means of corn seedlings (N = 5 samples), square root transformed.
v Corn shoot height was measured from the ground to the extended leaf.
w Corn shoots were dried in an oven at 60°C for one week and weighed.
x Radicle rot severity was visually assessed by estimating the percent area of rot on the radicle root.
y Seminal rot severity was visually assessed by estimating the percent area of rot on the seminal roots.
z Means followed by the same letter within a column and year are not significantly different at P value 0.10 using Fisher’s protected least significant difference.
Table 2. Average effects of winter rye treatments on density of Pythium spp. belonging to clade B in the soil collected from in the corn row and in the interrow in Grower 1's field.
|
|
|
Pythium clade B densitiesx |
|
|
Year |
Treatments |
Corn rowy |
Interrowz |
|
2019 |
|||
|
15-inch rye |
2.6 |
12.5 |
|
|
30-inch rye |
0.7 |
5.1 |
|
|
No CC |
0.0 |
4.0 |
|
|
P > F |
0.6145 |
||
|
2020 |
|||
|
15-inch rye |
3.6 |
6.6 |
|
|
30-inch rye |
86.7 |
4.8 |
|
|
No CC |
30.9 |
20.4 |
|
|
|
P > F |
0.4189 |
|
x Density is expressed as target pathogen ITS sequence copies per synthesized DNA, and is reported as copy number means, square root transformed.
y Soil was sampled directly in the corn row.
z Soil was sampled in the interrow approximately 15 inches away from the corn row
Table 3. Effects of winter rye cover crops on initial and final stand, barren plants, and yield of corn in Grower 1's field.
| Year | Treatments | Corn stand/A at V3w | Corn stand/A at R6x | Barren plants/Ay | Yield (bu/A)z |
| 2019 | |||||
| 15-inch rye | 31406 | 33193 | 1263 | 233.8 | |
| 30-inch rye | 31145 | 32627 | 1176 | 230.2 | |
| No CC | 32104 | 32017 | 2178 | 233.3 | |
| P > F | 0.3814 | 0.3481 | 0.3633 | 0.5383 | |
| 2020 | |||||
| 15-inch rye | 35416 | 35719 | 1493 | 171.1 | |
| 30-inch rye | 36070 | 36093 | 1120 | 172.6 | |
| No CC | 36026 | 35470 | 1369 | 173.5 | |
| P > F | 0.2838 | 0.8591 | 0.8236 | 0.4768 | |
w Corn stand counts were recorded within the first row of each 50 ft small plot at growth stage V3.
x Corn stand counts were recorded within the first row of each 50 ft small plot at growth stage R6.
y Barren plants were counted within the same 50 ft that stand counts were recorded at growth stage R6.
z Corn yield data were collected from all rows in each strip.
Table 4. Average effects of winter rye cover crop treatments on corn stand, and growth parameters of corn, radicle and seminal root rot, density of Pythium spp. belonging to clade B in radicles at growth stage V2 to V4, and yield in Grower 2's field.r
| Year | Treatmentss | Corn stand/A at V3t | Shoot height (cm)u | Shoot dry weight (g)v | Growth stage | Radicle rot severity %w | Seminal rot severity %x | Radicle clade B (copies) | Yield (bu/A)y |
| 2019 | |||||||||
| 1 | 32931 | 67.6 cz | 49.6 | 5.2 | 28.6 | 12.5 | 45.3 a | 236.8 | |
| 2 | 32118 | 72.8 ab | 55.9 | 5.2 | 20.0 | 10.5 | 19.6 b | 235.3 | |
| 3 | 32234 | 70.9 bc | 50.1 | 5.1 | 27.6 | 11.1 | 15.9 b | 233.4 | |
| 4 | 31468 | 69.1 c | 51.7 | 5.1 | 22.8 | 7.1 | 37.4 a | 238.8 | |
| 5 | 32409 | 77.7 a | 66.8 | 5.1 | 12.0 | 7.1 | 23.8 ab | NA | |
| P > F | 0.3268 | 0.0121 | 0.1847 | 0.7503 | 0.2132 | 0.6195 | 0.0877 | 0.8194 | |
r Density is expressed as target pathogen ITS gene copies per synthesized DNA, and is reported as copy number means of corn seedlings (N = 5 samples), square root transformed.
s 1= Early terminated 7-inch rye; 2= Early terminated 30-inch rye; 3= Late terminated 7-inch rye; 4= Late terminated 30-inch rye; 5= No rye control.
t Corn stand counts were recorded within the first row of each 50 ft small plot at growth stage V3.
u Corn shoot height was measured from the ground to the extended leaf.
v Corn shoots were dried in an oven at 60°C for one week and weighed.
w Radicle rot severity was visually assessed by estimating the percent area of rot on the radicle root.
x Seminal rot severity was visually assessed by estimating the percent area of rot on the seminal roots.
y Corn yield data were collected from all rows in each strip. NA= not applicable
z Means followed by the same letter within a column and year are not significantly different at P value 0.10 using Fisher’s protected least significant difference.
Educational & Outreach Activities
Participation Summary:
The results of our project were shared at the Department of Plant Pathology and Microbiology weekly seminar, the 2020 Annual American Phytopathological Society conference, and an ICM Blog. It was also presented at a field day in 2019. Posts on social media (Facebook, YouTube, and Twitter) linking to these outputs were done to share the research.
This project will be submitted to the Plant Disease Journal this year. It will also be included in the thesis titled "The effects of winter rye cover crop on corn seedling disease, corn growth and development in respects to winter rye seeding spacing" through Iowa State University.
Project Outcomes
Our project has provided an additional management practice when using a winter rye cover crop before corn. If some farmer's do see reduced corn yield after a winter rye cover crop, this winter rye spatial arrangement practice may reduce the negative impacts they see on corn yield. It may also encourage farmers to start using a winter rye cover crop before corn in their corn-soybean crop rotation.
I have learned that there are farmer's who do want to become more sustainable, but getting there is a challenge, whether that be from finances or practicality.