Final report for FW18-021
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.
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)
Cooperators
- (Educator and Researcher)
- - Technical Advisor
- (Educator and Researcher)
Research
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.
Analysis:
- Oak Knoll Aeration and Over Seeding Trial Report 2018
- Oak Knoll Aeration and Over Seeding Trial Report 2019
- Oak Knoll Aeration and Over Seeding Trial Report 2020
- Oak Knoll Haney Soil Test Results 2018-2019
- 3M_Zylstra Aeration and Chain Harrow Report 2021
Results:
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.
Continuation:
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.
Discussion:
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.