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What does it take to start a long-term experiment?

Posted by Molly McIlquham | December 13, 2022

Authors: Gabe LaHue, Assistant Professor of Soil Science & Deirdre Griffin LaHue, Assistant Professor of Soil Health & Sustainable Soil Management

Long term thinking

“What were they thinking?” It’s a common question asked by agricultural scientists about the design of long-term cropping system experiments. Starting a long-term study is a big investment and having asked those questions ourselves while working with multi-decadal trials, you can imagine how daunting it was to be tasked with setting up a Long-term Agroecological Research and Extension (LTARE) site through the Washington Soil Health Initiative (WaSHI). In 20 years, would people be wondering what the heck we were thinking.

An aerial image of the Mount Vernon long term site
The Mount Vernon Long-term Agroecological Research and Extension Site from the sky. Photo: Kwabena Sarpong

Luckily, we weren’t alone in this endeavor. The farming community in NW WA is strongly supportive of agricultural research and made sure that the new Mount Vernon LTARE site would be informed by their experience. Furthermore, plenty of researchers running long-term experiments across the United States were willing to share their insights and lessons learned with us.

One of the activities that kicked off the process was a soil health listening session held with stakeholders in December 2019 to identify key soil health challenges in NW WA and management strategies to address these challenges that farmers have tried or were interested in trying. Farming systems in NW WA are very diverse, and while the Mount Vernon LTARE focuses on a 4-year potato-based rotation, the prevalence of crop rotation in the region means that many of the soil health challenges are relevant across crops. Farmers identified soil crusting and compaction, poor water infiltration, and soilborne diseases among the top issues, for which more detail can be found in the Soil Health Roadmap. Cover cropping, soil amendments, modifying or timing tillage practices, and lengthening or adjusting crop rotations are just a few of the tools that farmers have tried or are using to combat these challenges. Therefore, these practices formed the backbone of our long-term experiment.

And one of the main take-home messages for us from the farmers? Don’t think too small and don’t be afraid to push the envelope. They can always adjust management strategies to make them economically viable, but we won’t get anywhere if we think small. Hence, the “moonshot” treatment, inspired by one of our Stakeholder Advisory Committee members: a treatment that is put into a three-year grass-clover perennial cover crop between potato crops, has no residue removal, and gets compost applied every four years. We’re throwing the kitchen sink at it.

Staying relevent

Speaking with the researchers in charge of other long-term experiments across the US, there was no shortage of things they would have done differently in setting up an LTARE. There’s always room for improvement! Two recommendations that stood out were choosing management practices to represent a continuum and designing for change. Essentially, both recommendations come down to ensuring that the Mount Vernon LTARE is relevant and stays relevant. Farmers have such varied production practices that no experimental design can represent everyone’s management systems… even if you had a billion dollars and hundreds of experimental treatments. However, by designing treatments to represent a continuum, rather than categorical systems, we can ensure that as many farmers as possible can find themselves along that continuum. In our case, the treatments center around a gradient of organic matter inputs and a gradient of disturbance, from a treatment that has no cover crops or compost application, has crop residues removed, and receives full tillage to a treatment that has a perennial cover crop, receives compost, has no residue removal, and is tilled only one year out of every four. So, a farmer who doesn’t apply compost, maintains crop residue, cover crops infrequently, and doesn’t use any reduced tillage practices is still represented, even if no treatment includes these exact practices.

Researchers using a hydraulic soil probe
Researchers at the Mount Vernon long-term site take a deep soil core using a hydraulic probe.

The second recommendation of designing for change is to ensure the Mount Vernon LTARE stays relevant. To that end, the experiment is organized around guiding principles (reducing disturbance, increasing organic matter) rather than specific management practices (such as no-till). This allows the management practices to adapt to ensure relevance as long as the guiding principles around each treatment are maintained. Similarly, the crops themselves in the experiment may change over time, particularly the crops planted in the three years between potato crops. Did you know that over 10,000 acres of green peas for processing used to be planted in Skagit County as recently as 1997? That acreage has disappeared completely, yet green peas would have certainly been included as a rotational crop if the Mount Vernon LTARE had been initiated 25 years ago. Agriculture is constantly evolving to stay viable, and therefore the experiment must also be able to evolve to stay relevant.

So, what does it take to start a long-term experiment?

In short, it takes incredibly supportive stakeholders, guidance from researchers around the country, and structuring the experiment to be representative and adaptable to ensure relevance. The next step is figuring out what it takes to keep a long-term experiment going!



Resources mentioned can be accessed at the links below:

National Agriculture Statistics Service Quick Stats

Washington Soil Health Roadmap