Evaluating the impact of aeration and over-seeding on soil health, forage quality and forage quantity in perennial hay pastures in Western Washington

Final report for FW18-021

Project Type: Farmer/Rancher
Funds awarded in 2018: $19,948.00
Projected End Date: 03/31/2022
Grant Recipient: Oak Knoll Farm
Region: Western
State: Washington
Principal Investigator:
Adam Greene
Oak Knoll Farm
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Project Information


Many pasturelands in western Washington are not actively managed or renovated after
the initial pasture seeding. Compaction, depletion of soil nutrients, and domination by
aggressive and unpalatable grass species lead to poor forage quality and reduced forage
quantity. Livestock producers recognize the need to improve pastures, but lack specific
information necessary to evaluate the risk and benefits of different pasture renovation
techniques. Conventional tillage and re-seeding is a lengthy, costly process that disrupts
soil structure and function and may favor invasive weeds, increase soil erosion, and
exacerbate loss of organic matter. A few producers practice annual aeration as a
management technique to oxygenate the soil, increase water infiltration, and improve a
seed bed. Research results on the effects of aeration vary widely. Variation in soil types,
climates, and vegetation also makes extrapolating data problematic. This leaves
producers with little data to assess the long-term impact on soil health or forage quality
and quantity, so the expense and risk of implementing this technique remain a barrier to
adoption. Sheep ranchers Adam Greene and Sarah Pope will perform field trials,
collecting data and demonstrating practices. Trials will focus on aerator use versus no use
(control) and compare over-seeding with and without aeration to unseeded areas.
Research design, data collection and analysis, and outreach support will be provided by
Dr. Brook Brouwer and Angie Freeman Shephard, MS of Washington State University
Extension San Juan County. This study will increase awareness of pasture renovation and
management best practices with a well-placed demonstration to other farmers/ranchers.
Information and results will be shared widely through field days, fact sheets, articles, and
on the extension website.

Project Objectives:

1. Measure how aeration and over-seeding impacts soil health for three years (Years 1-3)
2. Measure how aeration and over-seeding impacts forage quality/quantity (Years 1-3)
3. Measure establishment of over-seeded legumes in aerated vs. non-aerated (Years 1-3)
4. Quantify economics of aeration and over-seeding: cost to implement and estimated
value of benefits or negative impacts (Years 2-3, results published in Year 3)
5. Encourage pasture renovation by illuminating risks and benefits (Years 2 and 3)
6. Quantify adoption impacts using before-and-after questionnaires (Years 1-3)


Click linked name(s) to expand/collapse or show everyone's info
  • Sarah Pope (Educator and Researcher)
  • Dr. Brook Brouwer - Technical Advisor
  • Adam Greene (Educator and Researcher)


Materials and methods:

Oak Knoll Pasture Trial Methods

  • Soil Sample

    • Collect ~10 cores per plot to 12 in depth
    • Mix in 5 gallon bucket
    • Split sample in half, 1 for Haney test and 1 for agronomic soil test
  • Penetration resistance

    • Push penetratrometer into soil until 300 PSI using 1/2 cone tip
    • Record depth (inches) at which 300 PSI is reached
    • Repeat measurement 10x per plot
  • Percentage Ground Cover

    • Estimate % Bare Ground, % Litter, % Grass, % Legume, % Other forb, % Birdsfoot trefoil
    • Total may exceed 100%
    • Record values for 4 randomly placed quadrates per plot
    • If time allows, record species present—not critical
  • Infiltration test

    • Cut vegetation to ground level
    • Place 6in ring 3in into ground
    • Press soil against inside edge of ring
    • Lay plastic sheet
    • Pour 444ml of water into ring
    • Remove plastic and record time until water has infiltrated (Time 1)
    • Repeat (Time 2)


Additional Sites & Grant Extension:

Two additional sites, one on private land owned by the Three Meadow's Homeowners Association, and another at the Zylstra Preserve owned by the San Juan County Land Bank, were added in 2021.  This last-minute expansion was made possible because of extra funds left over from reduced activity in 2020 because of the COVID pandemic, and a no-cost grant extension by SARE to early 2022. 

These two additional sites were chosen as a more appropriate site for field restoration and improvements using aeration and chain harrowing equipment than the original Oak Knoll Farm site, based upon lessons learned and discussions with Drs Brower, Fransen, and Chaney.

These sites were setup, also based upon lessons learned, with longer and wider plots and better machine access coming into and leaving each plot to minimize rutting in and around the plots.  The Oak Knoll site was too tight, which caused machine rutting to occur at the edges of the plots because of machines needing to quickly get to speed and then quickly stop because of space constraints around the plots.  

Research results and discussion:



The analysis showed minimal improvements in aerated, harrowed, and overseeded plots.

In Year 1, potentially because of the late in the season aeration and harrowing which occurred after fall regrowth had started, the legumes in the aerated plots were knocked back and didn't develop as much as in the unaerated plots.

In all years, overseeding improved soil water infiltration. Aeration did not improve compaction or water infiltration, but there was a slight uptick in electrical conductivity and lower total N in the aerated plots after 2 years.


WSU Ext, along with private land owners and Oak Knoll Farm, plan to continue research at these additional sites over the coming years following similar and compatible methodology.  Forage, soil, and Haney tests will not be conducted on a yearly basis, because of cost constraints, but baseline forage, soil, and Haney tests will be taken at the sites in July '22.


Aeration has its place, but it is not a single solution for pasture management.  Aeration, by itself, was not shown to make notable improvements in soil health, water infiltration, or compaction in the soil types and climate at the Oak Knoll Farm test plot.  But there was enough learned about what not to do, as well as observations from other locations (including other pastures at Oak Knoll Farm) where aeration and harrowing have been used and looked beneficial, that WSU Ext., Oak Knoll Farm, other farmers, and private and government landowners are continuing the study on other sites believed to be more suited to aeration use.  These sites contain pastures which are in drier soils for more times of the year, have been heavily compacted and pugged from overgrazing and tractor use during wet seasons, and have less diversity of forage.  One of the sites allows managed grazing, while the other can only be used for haying.  The goals of aeration in these areas is focused less on directly improving soil health, than on breaking up pugged soils, and scratching the ground to promote more vigorous plant development.

This study also took place during surging interest in the county around pasture restoration and renovation.  This research helped shape the discussion around the benefits and use of various types of tools used, including the value of overseeding, tillage, minimal or no-till approaches, and managed grazing by large and small ruminants.

Participation Summary
4 Producers participating in research

Research Outcomes

3 Grants received that built upon this project
8 New working collaborations

Education and Outreach

6 Consultations
5 On-farm demonstrations
2 Online trainings
2 Tours
9 Webinars / talks / presentations
2 Workshop field days

Participation Summary:

130 Farmers participated
15 Ag professionals participated
Education and outreach methods and analyses:


  • Outreach: A farmer who owns and operates a local farm (all-year market garden and meat animals) was curious about the program and aeration.  She ended up borrowing the aerator and ran it in a more aggressive mode (blades out at 10 degrees and running over the same field at least 3 times at 7-9 mph).  She was very happy with how the alfalfa grew in that field that year and would like to try it again next year.
  • Tour: 9 individuals from the conservation district and Washington State Dept. of Ecology visited the farm to look at a separate project supporting no-till seeding practices in the county, which the farm is participating in.  They received an overview of the aeration project and toured the pasture.


  • Workshop: the 2019-Ag-Summit-Schedule_2019_01_08 occurred Feb 2nd and 3rd, 2019, and a half day session on "Pasture and Hayland Evaluation" was hosted at the farm, where this research project was highlighted and discussed.  The speakers were Marty Chaney, USDA-NRCS Agronomist, and Brook Brouwer, WSU Extension and this research project coordinator.  The event was very well attended with 31 folks attended, and in a post-session survey, the overall presentation received a 4.5 out of 5 rating and 70% of the attendees stated that they would make changes to their operation based upon what was presented.  
  • Workshop: Hay Field Improvement Workshop, Oct 11th, 5hr workshop with 2 hrs of classroom presentation and then 3 hrs at two different farm sites, one of which was Oak Knoll Farm. Dr Steve Fransen (WSU Forage Research Agronomist) was the primary speaker, with Dr. Brook Brouwer presenting the particulars of the research project. 30 folks were there for the session, with farms ranging in size from 5 to 300 acres for the session, and new farmers to those with over 40 yrs of experience. The overall presentation was rated as a 4.9 out of 5.
  • Presentation: Tilth Conference, Nov 10th, Yakima, WA “Western Washington Hay and Pasture Improvement”Panel: B. Brouwer, S. Bramwell, M. Habenicht.  24 session attendees.  On average respondents to evaluation “agree” with the statements, “My knowledge of the topic greatly increased”, and “Based on what I learned, I plan to make changes to my farm/business”
  • Consultations: Multiple consultations to farms within the county, discussing project to date, and lessons learned.  There was one in Feb, and then a number after S. Fransen's workshop.


  • Online Presentation: San Juan County WSU Extension office presented a 'Field Webinar Walk', discussing ongoing research in the county, including this project.  This presentation included an online zoom meeting where this project was discussed for 20 minutes.


  • Online Presentation (Feb) : San Juan County Conservation District held a 'No Till' Zoom workshop in Feb, where this research and tools used were discussed in the presentation in the context of other restoration options, and when aeration and harrowing are, and are not, beneficial to use.  
  • In Person Presentation (July): San Juan County Conservation District held a 'No Till Drill Training' on San Juan, Lopez, and Orcas Islands in July.  Adam Greene was present at the Lopez Training and gave the group a 5 min update on the research and general aeration pros and cons.  Bruce Gregory, of the Conservation District, passed that information along to the San Juan and Orcas Islands trainings.  
  • In Person Presentation (Sept): Gave an in-person field talk to members of the Three Meadow's Homeowners Association after presenting at their annual meeting (presentation)  Folks showed up for a 45 min presentation and walk about their pasture, managed and prescribed sheep grazing, and the SARE grant plot on their pasture.  
  • Presentation & Consultation (Oct): Submitted a presentation to the San Juan County Land Bank as a leasee as well as about the SARE/WSU Ext research plot on site (presentation), which was presented to the board.  There have been multiple conversations with the San Juan County Land Bank about aerating and harrowing pastures on two multi-hundred acre properties under their management, in the context of larger pasture renovation projects.  Some of these conversations were held in conjunction with Dr. Brower of WSU Ext and Bruce Gregory of the SJC CD.
6 Farmers intend/plan to change their practice(s)
20 Farmers changed or adopted a practice

Education and Outreach Outcomes

85 Producers reported gaining knowledge, attitude, skills and/or awareness as a result of the project
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.