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A decade of organic farming research for long-term solutions

PUYALLUP, Wash. – If you’re starting a new organic farm and you want to boost organic matter in your soil, you’ll want to invest in as much compost as you can. That’s just one finding from over a decade of research on organic farming systems by WSU soil scientists in Puyallup.

Winter squash grown organically at the WSU research farm in Puyallup.  Photo by Andy Bary, WSU.
Winter squash grown organically at the WSU research farm in Puyallup. Photo by Andy Bary, WSU.

Designed to help farmers improve their profitability and sustainability, the work sheds light on how different soil amendments, tillage practices and cover cropping systems impact soil quality, crop yield, nutrients and profitability with crops like lettuce, spinach, snap beans, broccoli, winter squash and wheat.
Evaluating soil changes in complex management systems requires multiple years, multiple rotation cycles, and multiple grants over the long haul.

“This year marks 11 growing seasons and with current funding, the research program will complete 13 growing seasons,” said soil scientist Craig Cogger. “That gets you a pretty mature system.”

Cogger and fellow soil scientist Andy Bary developed the long-term research program with extensive input from organic growers west of the Cascade Mountains.

“We wanted to help growers figure out which inputs will make organic systems more sustainable and profitable – which work better than others,” Bary said.

Cogger and Bary started the research program in 2003 on six acres of certified organic research land at the WSU Research and Extension Center in Puyallup, Washington. It is one of a handful of long-term research programs in the country focused on organic farming.

Here are a few highlights from the research:

Organic matter matters

Carbon is a major factor in overall soil health. Experiments showed that adding compost with a high-carbon content came out ahead compared to adding compost derived from chicken manure and bedding that was higher in nitrogen but lower in carbon. Adding high-carbon compost resulted in higher organic matter levels, lower soil compaction, and faster water infiltration, in addition to higher soil pH, more microbial biomass, and a larger bank of nitrogen in the soil organic matter – all of which add up to plants having a better chance of getting the nutrition they need.

Tillage tools, frequency and depth

A more surprising result noted by soil scientist Doug Collins was that tilling soil with a rotary spader, which turns the soil gently, did not result in less disturbance to soil life, compared to tilling with conventional equipment like a rototiller, plow or disc.

Blades of a rotary spader help protect soil structure. Photo by Doug Collins, WSU.
Blades of a rotary spader help protect soil structure. Photo by Doug Collins, WSU.

“From the soil biology perspective, tillage was tillage,” Collins said. However, in a pasture-based system where tillage was less frequent, the array of organisms living in the soil, or soil food web, was more diverse.

Where plots were tilled with the deeper reaching spader, soil compaction was reduced, making a better environment for plant roots. Cogger believes this may have contributed to higher vegetable crop yields in the spader-tilled plots in some years.

Suitable cover cropping

Growing a cover crop generally improves soil quality. But comparing three different cover crop systems revealed differences that can help growers choose the right system for their needs and, ultimately, increase their bottom line.

For growers who have enough land and want to raise livestock along with vegetables that don’t demand a lot of fertilizer like lettuce and squash, a pasture-based system could work well. A three-year rotation — grazing sheep and raising chickens on pasture planted with a grass and clover mix — required less tillage, reduced the need for added amendments, and resulted in higher soil microbial activity and a more diverse soil food web.

Planting cover crops between rows during the growing season – known as relay planting or interseeding – reduced the need for tillage compared with post-harvest cover crops. Relay cover crops are best suited for rotations where they don’t compete with crops such as fall lettuce or carrots that are harvested too late in the season to establish a post-harvest cover crop.

The bottom line

As long as adequate nutrients are provided, a variety of systems can produce good yields.

Andy Bary (left) and Doug Collins (right) take soil measurements in lettuce plots at the WSU research farm in Puyallup. Photo by Craig Cogger, WSU.
Andy Bary (left) and Doug Collins (right) take soil measurements in lettuce plots at the WSU research farm in Puyallup. Photo by Craig Cogger, WSU.

Except for crops the demand a lot of nitrogen in the pasture system, yields were similar across all experiments.

Net returns were greater than production costs most years in all of the systems. However, no one-size-fits-all. For broccoli, a high input system that included relay cover cropping, tilling with a spader, and high-carbon compost was most profitable. For winter squash, the pasture system with spader tillage was most profitable.

The path forward

The long-term organic farming research has inspired new research projects. Collins has started a reduced-tillage in organic agriculture experiment. Food safety specialist, Karen Killinger, is taking a closer look at tracking pathogens in the farming system to ensure safe foods. And research on greenhouse gas emissions in organic systems is underway.

As he prepares several publications summing up this long-term research, Cogger looks down the road and wonders,

Craig Cogger measures soil compaction. Photo by Doug Collins, WSU.
Craig Cogger measures soil compaction. Photo by Doug Collins, WSU.

“What does it take to maintain a system that has been built up with soil amendments? How long can we sustain these systems with lower inputs if we invest a lot up front?”

Cogger, who has been with WSU Extension for 30 years, expects to retire next year. He leaves a legacy of organic farming research and new questions to those, like Doug Collins, who will take up the mantle to lead the next ten years of organic farming research.

Media Contacts

Craig Cogger, soil scientist, 253-445-4512
Andy Bary, soil scientist, 253-445-4588