When an organic farmer needs to say goodbye to his cover crop and turn that field over to a cash crop, he’s got a few issues to consider.
With herbicide off the table for organic production, he could till the land—but conventional tillage has its downsides: It decreases organic matter, damages soil structure and costs time, fuel and wear-and-tear.
That’s where soil scientist Doug Collins comes in. As a Small Farms Extension Specialist for Washington State University’sCenter for Sustaining Agriculture and Natural Resources, Collins finds new ways to bring the benefits of reduced tillage to the state’s growing organic agriculture industry.
In honor of Washington Organic Week, Sept. 12 to 19, Collins answers questions below about his research on behalf of organic growers, looking for novel ways to integrate cover crops and work the land.
Why would organic farmers want to reduce tillage?
“Farmers go organic for a lot of reasons. For some, it’s an economic choice, such as a price premium. Others believe their crops are more nutritious and healthy. Just by using less pesticide, there’s less potential for water contamination or residue on the crops.
For organic farmers, tilling serves a lot of purposes. It kills whatever is growing at the moment and sets up an environment where you can come through with machines and cultivate.
But when you till, you’re exposing organic matter to faster decomposition. You’re turning weed seeds back to the surface where they are more likely to germinate. You’re also making more passes across the field, which means more fuel use and more greenhouse gas emissions.
Soil structure and aggregation are hurt by repetitive tillage. It can lead to erosion on steep slopes. We know larger-bodied organisms like earthworms, who play a unique role in the soil, are devastated by tillage.
In contrast, reduced tillage can improve soil quality by adding structure, more organic matter and larger worm populations. The benefits accrue over many years.”
What are the challenges for reducing tilling?
“One of the real challenges with both organic agriculture and reduced tillage is weeds. But even controlling a cover crop can be hard.
“Reduced tillage is widely used in conventional agriculture, but farmers use herbicide to make it work, both to control weeds and cover crops. In organic, it’s a challenge. You want to use cover crops for soil improvement, but you have to kill the cover crop to get a cash crop in.”
What techniques show promise?
“Two ways we’re exploring to terminate the cover crop without tillage are using a roller-crimper, and mowing. A roller-crimper crimps plant stalks every eight inches, killing the plant or halting its development. The other way is simply mowing it. Timing is important. You need to mow at a particular time to kill the crop.
One idea is that you grow mulch in place, kill the mulch, and that will suppress weeds. That idea is attractive to farmers.”
Do any cover crops look promising for reduced tillage?
“We’ve been very successful with vetch as a cover crop for broccoli. Vetch adds nitrogen to the soil, and broccoli requires a lot of nitrogen.
We’ve learned some great things with vetch that are applicable to no-till and conventional tillage. We know when we need to mow it—when it’s fully flowering. We know we need to let it fully flower to effectively terminate it. This later termination also works well for conventional tillage by supplying more nitrogen.
When you use cover crops or compost to build soil, you don’t get all that fertilizer benefit in one year. You create a bank of fertilizer in the soil. Farms that have been doing a lot of soil building should be able to reduce their use of fertilizer.
Our long-term experiment, now in its fourth year, compares traditional or conventional tillage with no-till and strip tillage. We’ve found that vetch works well with strip tillage.”
What is strip tillage?
“In strip tillage or zone tillage, you till an eight- to 12-inch strip, leaving one-third to two-thirds of your field undisturbed. You’re not disturbing all of the soil every year; you’re still making a pass, but using less horsepower.
In terms of adoptability, strip tillage is more likely to succeed. It looks more like what farmers are used to seeing. You can use conventional cultivation techniques in that strip, and farmers have tools on-hand for cultivating that clean ground.”
What other projects are you working on?
“Next spring, I’m doing an on-farm study, growing broccoli on five organic farms, two in central Washington, three in western Washington, looking at organic fertilizer rates and how they affect crop productivity.
We should see a curve where, as you increase fertilizer, yield increases to a point, then plateaus. I want to know: Where is that inflection point and is it different across farms? Is there any way to predict that, pre-season?”
Will reduced tilling catch on?
“There is a lot of excitement about reduced tillage. There are also a lot of challenges, and it’s difficult to make the leap. A lot of farmers are looking at what we’re doing and waiting. If we have a good example of a successful system, I see more adoption. Researching reduced tillage is about looking forward. We’re trying to invent things, take a concept and make it a reality.”
Links to learn more
• Learn more about reduced and conventional tillage practices with these Extension publications.
• Learn more about WSU’s Center for Sustaining Agriculture and Natural Resources here.
• Learn more about the College of Agricultural, Human, and Natural Resource Sciences here.