The Effects of Long-Term Cover Cropping Systems on Weed Communities
By: Elizabeth Oys
Dr. Liebman, Gina Nichols
Science with Practice Program, Department of Agronomy
Abstract
Cover crops are well-known for their ability to reduce soil erosion, improve soil health, and suppress weeds. Despite weed suppression being a potential benefit of cover-cropping, the long term effects of this system have not been quantified regarding weed seedbanks. The goal of this project is to better understand the effects on weed communities in cropped systems where the practice has been in place for ten or more years. Assessing the number and species of viable weed seeds in agricultural soils provides an indication of whether cover cropping actually affects weed dynamics in the long term. By quantifying long term benefits, the adoption of cover cropping may be more appealing to producers who seek to implement more sustainable practices for their operation along with associated environmental and economic benefits. For this project, we hypothesize that there will be significantly fewer weed seedlings emerging from soil collected where cover crops have been used than from where cover crops have been absent.
Methods and Materials
For this project, we have identified 3 different plots with cover crops established for 10 or more years where grain corn, silage corn, or soybeans are grown. They have a corresponding plot or field next to it or nearby that is without cover crops and is under traditional tillage methods. Each plot will have 20 soil samples collected from it, each are 10 cm deep and taken at various randomized locations at least 6 feet from the field edge. Randomized sampling is ideal because weed seedbanks are often random throughout any given field.
Field soil from each plot is taken and spread across 3 10x20" plastic trays with 1" of vermiculite on the bottom. Vermiculite ensures proper drainage of the soil, which is then saturated 3 times a day daily in a greenhouse. Seedlings that grow are recorded, both in numbers and species in each tray. After no more seedlings have emerged for a week, the current seedlings are removed and the soil is dried completely for about a week before resaturating and beginning the process again. This is repeated 4-5 times because weeds have adaptive strategies to emerge at various times during the growing season, and periods of drying and then resaturating will stimulate growth of different genotypes and species.
Personal Goals and Outcomes
My goals included:
•Experience how agronomic research is conducted and the components of sustainable agriculture in general.
•Gain a better understanding of the benefits of cover cropping systems.
•Quantify the effects of long term cover crops on weed fecundity.
My outcomes from the project were:
•Decided to pursue graduate school related to agricultural science in the future.
•Improved written, team, and interpersonal communication skills regarding research and professionality.
•Was exposed to a variety of sustainable agriculture projects and data collection methods.
•Gained an understanding on agricultural research statistics.
Preliminary Results
This project is currently still in the works. However, we have been able to identify visual differences in the trays between cover cropped fields and non-cover cropped fields. We took an initial count of seedlings in a non-cover cropped field, were there were 46 seedlings of the waterhemp species. In contrast, the cover cropped tray correlating to that same site had only 2 waterhemp seedlings. This difference is fairly constant between all of the sites and trays, so there are significant effects of the long term cover cropping system that will soon be quantified and we will run statistics on these differences. This supports our initial hypothesis and is exciting because this proves there are more than just environmental benefits of long term cover-cropping systems. The data we provide based on this project may even incentivize Iowan farmers to implement the practice on their farm in the future, as weed suppression effects are significant and it actually effects the in-soil weed seedbanks.
Conclusion
Aside from learning about sustainable agriculture and the amazing effects of cover crops, I have learned so much about myself and my interests thanks to the Science with Practice Program. It has opened my eyes to a new career and educational path and has further fueled my passion for sustainable agricultural practices. I feel more confident in understanding the research process and communication of scientific terms and findings, and I look forward to continuing to work within this lab and within the Department of Agronomy!
Acknowledgements: Thank you to Dr. Liebman and Gina Nichols for assistance and mentorship in this project, Van Wert Fund and Agronomy Department for funding of my experience, and SWP Team for their help.
Funding Organization: Practical Farmers of Iowa (PFI)
Duration: 04/29/2019
Principal Investigator(s): Matt Liebman