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

Progress 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
  • Sarah Pope
  • Dr. Brook Brouwer - Technical Advisor


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)



Participation Summary
4 Farmers participating in research

Educational & Outreach Activities

4 Consultations
1 On-farm demonstrations
1 Online trainings
1 Tours
2 Webinars / talks / presentations
2 Workshop field days

Participation Summary:

100 Farmers
15 Ag professionals participated
Education/outreach description:


  • 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.
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.