WaSHI Annual Report FY25

NW Washington Annual Cropping Systems LTARE

Mount Vernon, WA

Two people are working in a harvested field under a bright blue sky with scattered clouds. One person is standing and observing while the other kneels next to a large orange tractor equipped with a green soil sampling probe labeled “GIDDINGS.” The tractor has a large rear tire and is positioned on dry, cut crop residue. In the background, there are rows of crops, trees, and distant mountains. The scene suggests soil sampling or field research activity.
Liz Myhre, Agricultural Research Technologist, and Gabe LaHue, Associate Professor of Soil Science, using a hydraulic probe to take deep soil cores to measure soil bulk density and ultimately, soil carbon stocks. Photo by Betsy Schacht

This was an exciting year for the Mount Vernon LTARE because the 2024 season marked four years since the inception of the trial. This is significant because the site is based on a 4-year crop rotation, and as such, all experimental plots have now been through the full rotation. For example, each plot in the most aspirational treatment now has had a 3-year perennial cover crop and compost application.

With this benchmark, we conducted our comprehensive soil sampling in spring 2025, using a hydraulic probe to get deep soil cores (down to 4 feet). These samples were divided into subsections representing different depths and are currently being analyzed for a variety of soil health parameters including soil carbon, microbial biomass, and respiration (also known as mineralizable carbon). We also collected separate samples to look at physical soil properties including infiltration, water-holding capacity, and the stability of soil aggregates (individual units of soil structure) when exposed to simulated rainfall and ponding. These are key variables in a region where compaction and flooding are issues.

While we are not yet seeing improvements in infiltration from our soil health management systems, we have observed higher soil organic matter with Management System 4, where a 3-year perennial grass-clover cover crop is grown in the years between potato crops. Soil organic matter can take years to build, so it’s exciting to see measurable differences this early in the trial (Figure 1). 

A scatter plot titled “Spring 2024 – Wheat rotation phase” showing soil organic matter percentages across four management systems. The y-axis is labeled “Soil Organic Matter (%)” ranging from 2.5% to 5.0%, and the x-axis is labeled “Management System” with categories 1 through 4. Management System 1: Green dot around 3.1%, labeled “a” Management System 2: Yellow dot around 3.1%, labeled “a” Management System 3: Light blue dot around 3.6%, labeled “ab” Management System 4: Dark red dot around 4.4%, labeled “b” Each dot has vertical error bars, and smaller gray points represent individual data values. The chart indicates higher soil organic matter in Management System 4 compared to others.
Figure 1. Soil organic matter content across management systems in spring 2024 going into the wheat rotation phase. During this phase, System 4 is planted to a perennial grass-clover cover crop rather than to winter wheat.

Even more exciting, this difference in soil organic matter has started to translate into subtle, yet statistically significant, increases in soil moisture during the potato phase of the rotation (Figure 2).

A line graph titled “Summer 2025 – Potato rotation phase” showing volumetric water content (%) over time for four management systems. The x-axis is labeled Date with tick marks from June 30 to August 11, and the y-axis is labeled Volumetric Water Content (%) ranging from 0 to 40%. Four colored lines represent systems: System 1 (teal) System 2 (yellow) System 3 (blue) System 4 (red) Each line shows fluctuations with sharp peaks around July 14, July 21, July 28, and August 4, indicating irrigation or rainfall events. System 4 consistently has the highest water content, peaking near 35%, while System 1 remains lowest, around 10–20%. Shaded areas around each line indicate variability or confidence intervals.
Figure 2. Soil moisture (volumetric water content) across management systems in plots planted to potatoes during the 2025 growing season. System 4, which includes compost and a perennial grass-clover cover crop, has higher soil moisture than all other treatments during parts of the year.

In addition to soil properties, partnering scientists have been investigating the impact of our management systems on weed growth and weed seed banks, soilborne pathogen and nematode pressure, and beneficial and pest insect populations. Entomologist Louie Nottingham and M.S. student Adriana Barsan have found that the perennial cover crop (Management System 4) has increased the abundance and diversity of natural predator insects, including parasitoid wasps and mites, advantages that persist in the potato phase of the rotation.

Alt text: Four people are standing at the edge of a green crop field under a clear blue sky. Two individuals are positioned in the field, examining a plant sample, while the other two stand on the dirt path, one holding a camera as if recording or photographing the interaction. The field has tall green plants on the left and shorter crops on the right, with trees and distant mountains visible in the background. The scene suggests an agricultural site visit or field research activity.
Mount Vernon LTARE Co-Lead Deirdre Griffin LaHue being filmed in the Mount Vernon LTARE for an episode of Washington Grown, which aired in January 2025.

During this period, results from the Mount Vernon LTARE were presented at the annual meeting of the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America (2 presentations), the Entomological Society of America meeting, the Pacific Northwest Insect Management Conference, a WSU CAHNRS Regenerative Agriculture Showcase, the Western Washington Potato Workshop, and the 2024 Virtual SoilCon.

We also held a regional SoilCon event in December 2024 in conjunction with the Lynden Ag Show, with separate sessions focused on soil health in both red raspberry and potato systems.  This included a well-attended panel discussion with growers and researchers on the connections between soil health and soilborne pathogen management. In January 2025, our LTARE site was featured in an episode of Washington Grown focused on potato production.

A closeup image of Gabe wearing a white shirt and a black jacket, standing in front of a wood paneled wall.

Gabe LaHue

Washington State University

A woman in a green scarf smiling in front of a wooden wall.

Deirdre Griffin LaHue

Washington State University