Progress report for FW24-016
Project Information
Occultation tarping has the
potential to transform Oregon’s small farm management practices in ways that help farmers save money, access in-expensive, easy to implement strategies to terminate cover crops, and manage weeds in the field while protecting soil tilth. We want to study this ‘ground-breaking’ no-till strategy to better understand the impacts on soil health and plant termination.
Occultation, “weeding with tarps” involves laying down a thick, black plastic /vinyl tarp for 4-8 weeks. Under the tarp, the weed seeds germinate in the moist environment, plants die due to lack of sunlight, and then decompose back into the soil with the help of the active soil food web. Once the tarp is removed, the clean seed bed is planted/seeded and minimal soil disruption occurs.
Our research question is, “What effects does occultation have on plant termination and soil health?” We will contract with OSU Soil Lab to conduct soil tests encouraged by the Soil Health Institute to measure the effect of occultation on soil organic carbon concentration, carbon mineralization potential, and soil aggregate stability. These are all indicators of soil health.
Verdant Phoenix Farm’s team includes a professional educator / experienced no-till farmer, a retired PhD research advisor, farm assistant, and technical advisor / ag professional from Jackson Soil and Water Conservation District. Our project has significant support because there are a growing number of organic farmers interested in no-till, but they are not sure how to terminate plants and protect soil tilth.
We plan to share our findings through field days, on-farm demonstrations, and through interviews on the popular No-Till Growers podcast (reaching over 15,000 listeners weekly), and has over 275,000 YouTube subscribers, internationally. Our team will also develop a “Guide for occultation implementation: Occultation Protocol for No-Till Systems in Oregon” to share the practice in Oregon and beyond.
Project Research Objectives: Our project will determine if occultation tarping has a positive impact on:
- Soil organic carbon concentration, compared to tillage.
- Soil carbon mineralization potential compared to tillage.
- Soil aggregate stability compared to tillage.
- Plant termination by percentage. Qualitatively measure, through observation and photo documentation the percentage of plants terminated using a scale:1 = < 10%, 2= >20%, 3= <50%, 4=> 50%, 5= >90%
Education Objectives:
Objective 1: Develop case study, record observations, photo document, and record impact data on soil health, plant termination, and crop yield over the course of the project.
Objective 2: Establish educational field tours to demonstrate occultation techniques, impacts, and benefits to producers, gardeners, land managers, and ag professionals.
Objective 3: Plan, design, and write a fact sheet and publication to serve as a “Guide for occultation implementation: Occultation Protocol for No-Till Systems in Oregon”. We will work with the project team, our technical advisor, research advisor, ag professionals from SOU, JSWCD, and OSU Small Farms to collaboratively develop content and publish the Guide for use by other farmers and producers. (Letters of support included) This Guide will be available in print (at least 200) and our team will pursue publishing the fact sheet through OSU Extension.
Objective 4: Present
findings through in-field demonstrations and presentations for OSU Small Farms program, OSU Small Farms Conference, Jackson Soil and Water Conservation District (JSWCD) workshops, OSU Land Steward classes, Friends of Family Farmers, and others when requested. At least 100 people will attend.
Objective 5: Print anddistribute fact sheet / "Guide" through ag partners, technical advisor, and other community partners so that over 200 copies are provided to interested producers and ag professionals to increase the impacts of this research and broader adoption of the practices.
Objective 6: Prepare and deliver an online workshop / podcast to disseminate project findings via “No-Till Growers” podcast online. No-Till Growers have an active listening audience of approximately 15,000 weekly podcast listeners and 275,000 YouTube subscribers, internationally. No-Till Growers have committed to supporting this project (letter included) and their goal is to help promote and share no-till strategies so there is greater adoption of the practice.
WSARE Occultation Timeline:
Team: PI (Simes), Farm Assistant (Gooden), Technical Advisor "TA" (Bilbao), Research Advisor (Seidler)
|
April 2024 |
Research team convenes Purchase materials Measure and prepare plots “Before project” photos taken |
Research Advisor (Seidler) Technical Advisor (TA) (Bilbao) PI (Simes) Assistant (Gooden) |
|
May 2024 |
Collect Soil Samples from all plots Mail to OSU Soil Lab Record data from soil testing Occultation tarp applied and weighted down 4- 8 weeks application |
PI (Simes) Assistant (Gooden) |
|
June 1-15 2024 |
Remove tarp Observe plant termination Collect Soil Samples from all plots Mail to OSU Soil Lab Record data from soil testing |
PI Assistant |
|
June 15-30 2024 |
Seed Cash crop mix Water in seeds Record observations, take photos |
PI Assistant |
|
July-Oct 2024 |
Cash Crop Growing until frost Harvest cash crop, leave plant residue on plot |
PI Assistant |
|
Oct-Nov 2024 |
Post Harvest -observations about yield Collect Soil Samples from all plots Mail to OSU Soil Lab Record data from soil testing Occultation tarp applied 4- 6 weeks application |
PI Assistant |
|
November 2024 |
Remove tarp Observe plant termination Plant winter cover crop |
PI Assistant |
|
Jan- March 2025 |
Collect Soil Samples from all plots Mail to OSU Soil Lab Record data from soil testing Occultation tarp applied 4- 8 weeks application |
PI (Simes) Assistant (Gooden) |
|
March-April 2025 |
Remove tarp Observe plant termination Collect Soil Samples from all plots Mail to OSU Soil Lab Record data from soil testing |
PI Assistant |
|
May 2025 |
Seed Cash Crop mix Water in seeds Record observations, take photos |
PI Assistant |
|
July-Oct 2025 |
Cash Crop Growing until frost Harvest cash crop, leave plant residue on plot Post Harvest -observations about yield |
PI Assistant |
|
Oct-Nov 2025 |
Collect Soil Samples from all plots Mail to OSU Soil Lab Record data from soil testing Occultation tarp applied 4- 8 weeks application |
PI Assistant |
|
November 2025 |
Remove tarp Observe plant termination Plant winter cover crop |
PI Assistant |
|
Jan-March 2026 |
Harvest cover crop, plant residue on plot Observe yield Occultation tarp applied 4- 8 weeks application |
PI (Simes) Assistant (Gooden) |
|
April-June 2026 |
Remove tarp Observe plant termination Collect Soil Samples from all plots Mail to OSU Soil Lab Record data from soil testing |
PI Assistant |
|
June-July 2026 |
Seed Cash Crop mix Water in seeds |
PI Assistant |
|
July-Oct 2026 |
Cash Crop growing Harvest cash crop, leave plant residue on plot Record observations, take photos Collect Soil Samples from all plots Mail to OSU Soil Lab Record data from soil testing |
PI Assistant |
|
Nov-Dec 2026 |
Occultation tarp applied 4-8 weeks application Remove tarp Observe plant termination Seed Cover Crop Begin planning: outline for “Guide to Occultation” |
TA (Bilbao) PI (Simes) Research Advisor (Seidler) |
|
Jan-March 2027 |
Cover crop growing Occultation tarp applied 4-8 weeks application Begin compiling data On-farm workshop planning |
PI Assistant Research Advisor (Seidler) |
|
March-April 2027 |
Remove tarp Observe plant termination Final soil tests Compile soil testing data Record observations, take “after” photos “Guide” is complete and printed Distribute to ag professionals, partners, and farmers Podcast with No-Till Growers |
TA (Bilbao) PI (Simes) Assistant (Gooden) Research Advisor (Seidler) |
Cooperators
- - Technical Advisor
- - Producer
Research
This project addresses, “how does occultation impact soil health and plant termination?”
Project Site: Verdant Phoenix Farm, is 9 acres on Hartley Road in Phoenix, Oregon, just South of Medford, Oregon in Zone 8a: 10°F to 15°F. In 2020, all 9 acres of the property were burned to the ground in the Alameda Fire which destroyed 2,000 structures locally. The project site has Medford silty clay loam, a common soil type in the region, it has been fallowed for 16 years, and is now transitioning to organic certification through Oregon Tilth (2024).
Project Research Objectives: Our project will determine if occultation tarping has a positive impact on:
- Soil organic carbon concentration, compared to tillage.
- Soil carbon mineralization potential compared to tillage.
- Soil aggregate stability compared to tillage.
- Plant termination by percentage. Qualitatively measure, through observation and photo documentation the percentage of plants terminated using a scale:
1 = < 10%, 2= >20%, 3= <50%, 4=> 50%, 5= >90%
After pursuing these research objectives, our team will develop a “Guide for occultation implementation: Occultation Protocol for No-Till Systems in Oregon” and fact sheet.
Project Plot Design: This study will include an experimental design with seven blocks; five treatment plots, tilled plot, and control plot. Each plot will be 10 feet x 20 feet to ensure the 10 foot x 20 foot tarp covers the entire plot. The control plot will be un-tarped and not tilled, 1 plot will be tilled using a rototiller, and five plots will have occultation treatments for 4-8 weeks depending upon the smothered plant termination rate. We will use photo-documentation to track progress and impacts. There is no known fertility gradient in this field which has consistent soil type, soil conditions, and does not have slope.
Project Research Methods:
- The experimental design will be a side-by-side comparison. We will maintain the same crops in both the treatment and control plots. Each plot will be 10 feet wide and 20 feet long, the same size as the occultation tarps (10’x 20’). Each will be mowed to prepare, and we will mow between the plots to manage 4-5 ft wide paths.
- Soil Health Measurements (as suggested by SHI) and administered by OSU Soil Lab will be taken at regular intervals on each of the 7 plots, each year. There will be five soil samples taken from each of the 7 plots using an “M” shaped corner sampling design, mixed, and then mailed to the soil lab for the “Basis Soil Health tests.” These values will be compared year over year (for 3 years) to establish if there is a change in soil health over time with the use of occultation tarps. The PI will lead this process to make sure all the steps are executed correctly, and impacts are reported.
- Five plots will implement Occultation, which utilizes black tarps to starve plants of sunlight and limit the plant's ability to photosynthesize for 4-8 weeks prior to planting into it.
- The PI will use the same production methods in the control, tilled, and five treatment plots, except that the treatment plots will have an occultation application prior to planting/seeding. The tilled plot will be managed using typical tillage (e.g., tilled with a rototiller right before planting/seeding to a depth of 5-6 inches). Once the tilled and treatment plots are seeded with the cash crop, they will both be irrigated & cultivated the same (overhead, weeded by hand with hula hoes, etc.). There will be 6 plots, and 1 control plot to study the impacts on soil health. Optimal tarp application time is defined at the sufficient time to terminate up to 90% of the existing vegetation in the plot.
- In each plot, except the control, cash crop seeds will be planted in spring, by broadcasting and covering a mix of daikon radish, bush beans, basil, and popcorn. Then cover crop, fava bean and grain seeds, will be planted in the fall, for winter/ early spring soil coverage. Crop residue from harvest will be returned to the plots. The bean and corn seeds will be soaked in water 24 hours before planting.
- Data will be compiled from soil tests, and data will be collected by observation on the percentage of plants terminated for each plot, as well as yield amounts. These values will be tracked and compared year over year to establish if there is a change in soil health and plant termination with the use of occultation tarps.
Soil Sampling: Soil samples will be taken prior to the application of the tarps to establish a baseline in soil data, and then before and after occultation tarps are applied through the first frost. Five soil samples will be taken in each plot with a 1-inch soil corer to a depth of 8-10 inches, a 6-inch (15 cm) soil specimen will be cut from the core and pooled for each plot to make a sample. The sampling area for the plots will be 2 feet from the perimeter of the tarps on each side to avoid edge effects within the plot. We will have seven plots/replicates for each soil test which will be analyzed by OSU Soil Lab’s “Basic Soil Health Assessments” (Fee schedule included) and based upon recommendations by Soil Health Institute (SHI). SHI suite of measurements that are responsive to soil health promoting practices, including soil organic carbon concentration, carbon mineralization potential and aggregate stability including:
- Total C&N (dry combustion) assume Total C = SOC
- Organic matter estimated, Total C, Pribyl et. al 2010.
- Wet aggregate stability, Cornell sprinkle infiltrometer
- Respiration using a Picarro G/C
These tests will be conducted for each soil sample from each of the seven plots before and after each occultation treatment (3 per year).
Together, these indicators reflect soil’s ability to support biomass production; store, filter, and transform nutrients and water; host biodiversity; and regulate Carbon pools. Thus, these tests will reflect if soil health is increasing in the study area.
Previous Occultation Research:
-
OW19-345, California, 2019.
-
FNE21-984, Vermont, 2021.
-
Bulletin # 1075, Maine
Research Outcomes
Update 3.2025:
Verdant Phoenix Farm’s farmer-led trial research reflected that occultation tarping resulted in terminated weeds, and higher soil moisture levels. In the same plots, soil carbon, nitrogen and respiration rates were reduced under occultation, which is inconsistent with what we predicted. Tarping was beneficial in terms of weed suppression and crop termination. Verdant Phoenix Farm will continue the practice of occultation tarping, and will conduct further research to evaluate the practice over multiple growing seasons.
Vinyl tarps were applied to 10x10’ subplots for six weeks, and then removed for planting. When the tarps were removed, in-tact organic matter was present on the soil surface (long dead grass covered the soil). This residue was tilled into the plots with the use of a walk-behind tiller, however in the no-till plots the carbonous material persisted and served as a carbonous mulch in those plots. After the tarps were removed, plots receiving the tillage treatment were tilled, and the no-till plots remained ready to be seeded (with the mulch on the surface). A polyculture mix of seeds was then planted in all blocks. Soil samples were collected from all subplots in early July. Visual observations (% cover) and photo documentation of weed and polyculture crop cover were noted in each subplot four and six weeks after crop planting (data not shown).
Soil samples were sent to the Oregon State University Soil Lab for soil tests recommended by the Soil Health Institute to measure soil organic carbon concentration, carbon mineralization potential, and soil aggregate stability. These are all indicators of soil health, and they directly impact the yield and profit of organic farms, including Verdant Phoenix.
Also, we evaluated weed termination and crop germination through observation, photo documentation, and an online tool called https://canopeoapp.com to evaluate the percent coverage of both weeds and the seeded polyculture.
Effects of Tarping in Tilled Plots
Under tillage, organic matter levels were relatively high (average 10.2%) as was total (organic+inorganic) nitrogen (0.42%), which may be reflective of a high level of crop residue that was incorporated during the tillage operation, and could have impacted the soil samples submitted to the OSU Soil Lab.
Tarped plots that were tilled were higher in soil moisture (27% vs. 6% in untarped plots), presumably from the moisture trapping effect of the tarp.
After six weeks of tarping, tarped plots were lower in percent organic matter (OM) and total nitrogen (N), and exhibited a lower CO2 burst at 24h (soil respiration) compared to untarped plots (Table 1). This is the opposite of what was expected, and is indicative of lower soil biological activity under the tarps (at the time of testing) on this farm after the organic matter was incorporated by the soil food web. The mechanisms that drive changes in the soil environment under occultation tarps are not well understood, and different soil health tests may be required. Previous occultation studies have produced inconsistent results, and it is suggested that a combination of factors such as ambient temperature, climate, tarping duration, amount crop residue and the soil to plastic contact may affect the soil environment (Birthesel et al. 2019, Rylander et al. 2020). However, none of the previous studies focused on no-till, organic systems, and many were tilled first and synthetic fertilizers added before tarping.
It would be valuable to conduct further assessments to determine whether this pattern repeats itself in another growing season, how soil biological activity is active during the time the tarp is present, and how it bounces back over time (after tarp removal), and how soil temperature was affected by tarping.
In terms of weed biomass and subsequent crop germination, Verdant Phoenix Farm observed that the tarped plots had significantly lower weed pressure, and higher levels of crop germination, which may be due to lower weed competition and higher levels of soil moisture conserved by the tarps.
- The use of tarps did successfully terminate weeds without the use of tillage.
- Not only did the tarps prevent the use of herbicides and tillage to terminate weeds or cover crops, but it also increased (or protected) soil moisture which supported the germination of the cash crop.
- The use of tarps may temporarily suppress biological activity.
- Under tarping, tillage did not have an effect on any of the soil health indicators, suggesting that tarping is a protective practice.
Future experiments could examine the effect of tarping on: soil temperature, the microbial community composition through PLFA testing, soil biological activity over time following tarp removal, and subsequent crop yield and quality.
update 3.2025: including initial soil tests, soil tests after tarping, and online tool generated images of percent coverage of soil (showing termination of weeds and cover crop germination)
225055 Simes Final Report.xlsx - S. Report
224311 Simes Final Report (2)
Education and Outreach
Participation Summary:
Ultimately this project seeks to produce the information necessary regarding a crucial step in the Cover Crop-Based, Tarped, No-Till Management System (CCTNT) for farmers. Occultation is significant because with minimal up-front investment, small-scale organic farms could significantly reduce labor and tractor costs, improve soil health, have higher profit, implement an environmentally friendly practice that terminates plants, and causes less wear and tear on their bodies.
Educational Background: Our project is unique because the PI and lead farmer for this project has a Masters in Science in adult education. Rhianna Simes, M.S.Ed., the project PI, spent ten years teaching for Oregon State University Extension, and has taught soil science, soil health, plant pathology, regenerative farming in the surrounding counties (in person) and through online webinars to hundreds of people. Rhianna is a professional educator who wrote her thesis on how to help adults change their behavior related to natural resource management. She is published, she has attended multiple soil-based trainings, she facilitated (and taught in) the international Soil Symposium in 2021, and has a personal passion for soil health.
In addition, Rhianna also has experience implementing WSARE projects, and is currently providing administrative support for a WSARE funded project related to drought tolerance for heritage grains and seeds. Rhianna is experienced, qualified, and excited to offer on-farm education as a result of this research to help other farmers understand how to implement no-till farming through the use of occultation tarping. Rhianna included her resume in the "Other documents" in order to demonstrate her capability to conduct this research, offer quality educational on-farm demonstrations, and produce the resulting How-to "Guide".
Target Audience: We intend to reach a diverse audience with this project from underserved communities, agricultural professionals, producers, farmers, land managers, ranchers, and others. We live in a rural, under-resourced region with a vibrant agricultural community that is spread out in a geographically large region. In order to extend the educational workshops to farmers and ag. professionals we plan to host virtual workshops, and guest presentations on No-till Growers Podcast. We also plan to offer in-person, on-farm demonstrations to help farmers and ag. professionals to see, experience, and understand the practice of Occultation tarping and its impacts on plant termination and soil health.
Education Objectives:
Objective 1: Develop case study, record observations, photo document, and record impact data on soil health and plant termination over the course of the project.
-update 3.2025: Objective 1 is underway. We are recording observations, photo documenting and tracking the soil health and plant termination data. We have tracked qualitative data for the crop yield in each block.
Objective 2: Establish educational field tours to demonstrate occultation techniques, impacts, and benefits to producers, gardeners, land managers, and ag professionals.
-update 3.2025: Objective 2 is planned for 2025. We will be hosting field tours to demonstrate occultation on Verdant Phoenix Farm and on 2 other farms in the Rogue Valley. We will share the technique and its benefits in these on-farm field days.
Objective 3: Plan, design, and write a fact sheet and publication to serve as a “Guide for occultation implementation: Occultation Protocol for No-Till Systems in Oregon”. We will work with the project team, our technical advisor, ag professionals from SOU, JSWCD, and OSU Small Farms to collaboratively develop content and publish the Guide for use by other farmers and producers. This Guide will be available in print and our team will pursue publishing the fact sheet through OSU Extension.
-update 3.2025: Objective 3 is planned for 2025. We have been gathering the photos, references, and protocols for the fact sheet on Occultation tarping. We are actively collaborating with partners on the content and timing for this educational product.
Objective 4: Present findings through in-field demonstrations and presentations for OSU Small Farms program, OSU Small Farms Conference, Jackson Soil and Water Conservation District workshops, OSU Land Steward classes, Friends of Family Farmers, and others. At least 100 people will attend.
-updated 3.205: Objective 4 is still in the planning phase.
Objective 5: Print and distribute fact sheet / guide through ag partners, technical advisor, and other community partners so that over 200 copies are provided to interested producers and ag professionals to increase the impacts of this research and broader adoption of the practices.
-update 3.2025: Objective 5 is being planned and developed. As we conclude the trial and compile the data and photos we will use this content for the fact sheet that will be shared widely.
Objective 6: Prepare and deliver an online workshop / podcast to disseminate project findings via “No Till Growers” podcast online. No Till Growers have an active listening audience of approximately 15,000 weekly podcast listeners and 275,000 YouTube subscribers, internationally. No Till Growers have committed to supporting this project and their goal is to help promote and share no till strategies so there is greater adoption of the practice.
-update 3.2025: Objective 6 is still planned.
Educational Resources: After pursuing our research objectives, our team (in collaboration with OSU Extension and JSWCD) will develop a fact sheet and “Guide for occultation implementation: Occultation Protocol for No-Till Systems in Oregon” to increase the outreach, engagement, and educational impacts of our project. This fact sheet / Guide will be distributed at workshops, farm tours, conferences, and by agricultural professionals as an educational resource for other farmers and technical assistance providers/ professionals.
-update 3.2025: Development of this educational resource is planned for 2025. We have gathered photos, testimonials, and we continue to collect data for this fact sheet.
This project is expected to increase the number of farmers capable of implementing no-till farming through occultation tarping, and we will demonstrate improved strategies for terminating plants and improving soil health. This project will increase the adoption of no-till management practices that result in healthier soils in Oregon and beyond.
update 3.2025:
Effects of Tillage in Tarped Plots
Under tillage, organic matter levels were relatively high (average 10.2%) as was total (organic + inorganic) nitrogen (0.42%), which may be reflective of a high level of crop residue that was incorporated during the tillage operation, and could have impacted the soil samples submitted to the OSU Soil Lab.
Tarped plots that were tilled were higher in soil moisture (27% vs. 6% in untarped plots), presumably from the moisture trapping effect of the tarp.
Verdant Phoenix Farm observed that the tarped plots had significantly lower weed pressure, and higher levels of crop germination, which may be due to lower weed competition and higher levels of soil moisture conserved by the tarps.
Comparisons of tilled and untilled plots under tarping did not produce statistically significant differences in the soil environment (Table 1). This suggests that the tarping helped to mitigate the drying effects of tillage, and kept soil OM, N, and respiration more consistent.
Soil health measurements are a snapshot in time, but they can help farmers understand the impacts of their management activities. Moreover, preliminary data gathering and review allows us to refine our questions and helps us to truly assess management practices. As well, plant termination measurements are important because they help farmers to identify which weed/ cover crop termination method is appropriate for their operation. Many organic, no-till farmers rely upon manual labor to address unwanted plant pressure, which is expensive and depends upon labor availability.
- The use of tarps did successfully terminate weeds without the use of tillage.
- Not only did the tarps prevent the use of herbicides and tillage to terminate weeds or cover crops, but it also increased (or protected) soil moisture which supported the germination of the cash crop.
- The use of tarps may temporarily suppress biological activity.
- Under tarping, tillage did not have an effect on any of the soil health indicators, suggesting that tarping is a protective practice.
The Education components of our project are planned for 2025 and will be held in partnership with Jackson Soil and Water Conservation District.
The project did allow the PI to work with the Organic Farming Research Foundation on Occultation Tarping. They shared about this project throughout their program. The final report is included here.
Education and Outreach Outcomes
update 3.2025:
The mechanisms that drive changes in the soil environment under occultation tarps are not well understood, and different soil health tests may be required. Previous occultation studies have produced inconsistent results, and it is suggested that a combination of factors such as ambient temperature, climate, tarping duration, amount crop residue and the soil to plastic contact may affect the soil environment (Birthesel et al. 2019, Rylander et al. 2020). However, none of the previous studies focused on no-till, organic systems, and many were tilled first and synthetic fertilizers added before tarping.
It would be valuable to conduct further assessments to determine whether this pattern repeats itself in another growing season, how soil biological activity is active during the time the tarp is present, and how it bounces back over time (after tarp removal), and how soil temperature was affected by tarping.
-Educational activities will occur later in 2025
ability to terminate weeds without tillage