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Zebarth’s trials involved the use of five different compost types in small plot trials. (Photo: AAFC)

Soil Health Key for Long-Term Potato Production

A key feature of healthy soil is the quality and quantity of soil organic matter.

Across North America, most potato crop yields have been on the rise in the past few decades. In parts of Canada though, data has revealed that yields in some areas have either decreased or remained stagnant, especially in New Brunswick.

Soil scientists attribute this to waning soil health due in part to short rotations and soil erosion. As a result, improving soil health is top of mind for many producers.

The Importance of Soil Health

While a soil test provides information like nutrient content and pH level, generally it won’t reveal some of the more vital information, such as water availability and infiltration. Healthy soil has the ability to hold plant-available water, which is especially important during times of water stress. Healthy soil also aids in water infiltration, which is essential for minimizing erosion due to heavy rainfall.

A key feature of healthy soil is the quality and quantity of soil organic matter. Along with its contribution to overall soil structure, soil organic matter also provides valuable nutrients for crops and supports microbial life.

Soil health is also thought to be a key contributor to yield, which is why Agriculture and Agri-Food Canada (AAFC) scientists are working on a four-year project in New Brunswick to improve soil health. AAFC research scientist Bernie Zebarth says the goal of the project was to look for ways to increase soil organic matter in a short period without causing environmental damage.

Working in collaboration with McCain Foods (Canada), as part of a larger project with funding from several partners, including the P.E.I. Potato Board, Potatoes New Brunswick and the Manitoba Horticulture Productivity Enhancement Centre, Zebarth and his colleagues looked for sources of compost in the area in large enough volumes for commercial use.

Five products were chosen for testing: marine-based compost; poultry manure compost; a compost made with forestry waste and poultry manure; a forestry residues compost; and, separated organic waste compost. Unfortunately, according to Zebarth, there was no yield response with any of the composts in the small plot trials, a result likely due to limited moisture stress. In the field-scale trials, which only used one type of compost chosen by industry (a compost made with forestry waste and poultry manure), a modest yield increase was seen, on average.

Zebarth thinks yield boosts were modest partly because there weren’t many available nutrients in the compost they used. He noted there was only a small increase in water-holding capacity; however, there was a “nice, measurable increase in water infiltration.”

The researchers looked at soil health on a molecular level as well. Claudia Goyer, AAFC molecular bacteriologist, evaluated microbial populations pre- and post-application using next generation sequencing. She saw quite a dramatic effect on bacterial activity post-application, and smaller effects that lasted over the year following application.

The researchers also evaluated how the compost increased yield in the rotation crops, the most popular being barley, to see if there was a yield increase there as well. The increases they saw were modest. “In the field-scale trials, at this point, the increase in yield would not pay for the cost of the compost,” says Zebarth. “And that’s based on three years of field-scale research.”

McCain Foods was an important partner in the AAFC project. According to Gilles Moreau, McCain Foods agronomist, the company buys about 60 per cent of New Brunswick potato crops, so they have a vested interest in seeing those yields increase. Moreau says their interest is more than yield related. In fact, he puts soil health on the top of the list of things farmers should focus on.

“I’ve always been a soil person,” says Moreau. “It’s like putting the pieces of a puzzle in place. If your first piece doesn’t fit right, then none of the other pieces will fit on top of it. So if your soil is not right, you have a bad starting point.

“There’s a lot of talk about technology, yield monitors, drones,” he adds. “Put money in your soils. You don’t need to have more high-tech equipment. All those gadgets aren’t going to pay for themselves if you have soils that are degraded and tired.”

Improving Soil Health

Charles Emre, a southwestern Ontario potato farmer, has been experimenting with his soils for the past two decades. His 700-acre farm is in the sand plains of Norfolk County on land that was once heavily fumigated for tobacco production.

“When we first started working in these soils you couldn’t find an earthworm if your life depended on it,” he says. “We now have earthworms again.”

Today, Emre grows potatoes in a 24-month cycle: 12 in potatoes and 12 in a cover crop. In spring, he plants mustard, incorporating it into the soil in mid-June. Doing so improves soil organic matter and suppresses nematodes. His soil also has better moisture-holding capacity. Even in last summer’s extreme drought, Emre says his crop did pretty well.

As the health of his soil improves, Emre says his need for pesticides and fertilizers is also reduced. He also believes he has better control of Verticillium wilt.

But is there a return on investment? When he first made the decision to focus on soil health, Emre was growing grain crops such as rye and wheat. “There was a little bit of income,” he says. “But I had to ask myself what type of farmer I was, grain or potato? We decided potatoes was the answer.”

While Emre notes he’s not qualified to give recommendations, he does advise growers to be patient and to not be afraid to try. He also suggests connecting with others who put soil health first.

“When I first started, there was no information at the time, but there is now,” he says. “I was the village idiot around here for a while for growing all these goofy crops. Is a mistake truly a mistake if you learn something?”

Emre isn’t the only potato farmer who is trying to improve soil health. Nolan Masser, a grain and potato farmer from Pitman, Pa., has been experimenting for the past two years. He’s planted a multi-species cover crop in the hopes of addressing water infiltration and soil loss on the farm. He’s even tried minimum-till planting, an experiment that required him to modify a subsoiler with a pipe.

“I knew we had problems. I knew our soil loss was way too high,” says Masser. “We converted everything but potatoes to no-till but things weren’t getting better. We weren’t holding water; I knew we had to do something. If we kept the soil loss where it was there would be no farm.”

Masser’s ultimate goal wasn’t just to improve soil health, but also to cut chemical fertilizer and pesticide dependence by 50 per cent. He’s well on his way. In fact, over the past two years he has noticeably reduced the use of pesticides on his farm.

“It has to be a change of attitude first. You need to change your whole attitude for production, and that’s a difficult thing,” says Masser. “We need to unlearn what we’ve done and learn new things. People look at you weird. At first it was a struggle getting my own family to understand the new program.”

But it’s working. Masser can see that his soil is improving. “I can see our farm is doing better now. But it’s nowhere near where it should be. We’re learning what not to do.”

Unlearning years of production practices isn’t easy. No one knows this better than Blake Vince, an Ontario-based grain farmer, who says there are three steps to improving soil health. First, it’s important to have a living plant in the soil 12 months of the year. Second, the soil should be disturbed as little as possible. The third step is to significantly reduce the use of herbicides, pesticides and fungicides.

Vince, a Nuffield Scholar who focused his studies on soil health, understands that making these changes is not easy and that growers will have a lot of questions. He recommends finding a good mentor, within Canada or beyond its borders.

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