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In upcoming projects, Comeau will be determining if the soil organic matter balance is positive or negative due to different agronomic practices. (Photo: Wayne Riley, AAFC)

Boosting soil carbon, boosting potato yields

A soil carbon scientist is teaming up with other researchers in the Maritimes to work on practical ways to revitalize soil health and increase productivity.

Louis-Pierre Comeau is adding the soil carbon piece to Agriculture and Agri-Food Canada’s (AAFC) research efforts in the Maritimes. His studies will be contributing to the development of practical, profitable agricultural practices that increase soil organic matter for improved potato yields.

Carbon is part of all plants and animals, and the key element in soil organic matter.

“In turn, soil organic matter is essential for a variety of needs like food, fibre and biomass production, the development of new antibiotics, and the provision of essential ecosystem services such as water filtration. In agriculture, soil organic matter regulates plant nitrogen-use efficiency, stores and supplies other nutrients essential to plants and soil organisms, holds soil particles together, reduces soil erosion risk, improves the soil’s ability to retain and transmit water for healthy crop growth, and provides a porous medium for root growth,” says Comeau, a research scientist who joined AAFC’s Fredericton Research and Development Centre (FRDC) in 2017.

When Comeau first started at FRDC, he spent some time travelling in the Maritimes to learn more about the region’s agriculture and soils. “I did my Masters degree in Saskatoon, my undergrad in Mexico, and my PhD in Indonesia, so the Atlantic region was a new ecozone for me. I think the farmers here are really dedicated because this is a very tough region for agriculture due to the shallow and coarsely textured soils, the sloping terrain and the challenging climate.”

Loss of soil organic matter is a serious concern in the region. “No scientific survey has been done to precisely quantify the loss of soil organic matter in New Brunswick. However, we have a large amount of empirical evidence that, on average, the percentage of soil organic carbon decreased from above three per cent to below two per cent in recent decades,” he explains. “Generally, organic carbon levels above three per cent are good for crop production.”

Over those same decades, potato yields in the Maritimes increased only very slowly, while various other potato-growing regions in North America experienced much stronger yield increases. For instance, from 1988 to 2017, average potato yields in New Brunswick rose from 260 to 310 hundredweight (cwt) per acre. Meanwhile in Alberta, potato yields increased from 270 to 391 cwt/acre, and those yield increases coincided with rising soil carbon levels.

“The lower potato productivity in the Maritimes has been linked to high disease pressure, but high disease pressure is associated with low soil organic matter,” he notes. “Soils with high organic matter levels tend to have fewer disease problems because they have more diverse, balanced soil microbial communities. Conversely, in a soil with low soil organic matter, crop diseases tend to be more of a problem because soil-borne pathogens have fewer or no competitors.”

Comeau points out that soil organic matter gains and losses both involve positive feedback loops. “Soil organic matter is composed, in part, of decomposing plant residues so it is important to have good biomass production and to return the crop residues to the soil to build organic matter. That allows more plants to be grown, which produce more crop residues, resulting in more organic matter and less likelihood of erosion. Alternatively, the less organic matter you have, the harder it is for plants to establish and grow, the fewer the crop residues, and the higher the erosion risk.”

Growers in the Maritimes are looking for ways to address the interrelated problems of low soil organic matter and stagnant potato yields.

“Farmers and companies like McCain and Cavendish are well aware that around 50 per cent or more of the organic matter has been lost. And they know this loss is hampering the land’s productivity.”

Comeau and other AAFC researchers – including experts in agronomy, soil microbial communities, soil nutrients and other research areas – are collaborating on several projects to develop and assess beneficial management practices (BMPs) that result in more productive soils and better yields under the growing conditions in the Maritimes.

“My speciality is to quantify soil organic matter, or soil carbon, which is a complicated task, and to understand why and how soil organic matter is generated and how it is decomposing. The scientific community is just starting to understand soil organic matter dynamics,” explains Comeau. “Accordingly, my job is mainly to do soil organic matter accounting, both spatially and temporally, in the region. In other words, I determine if the soil organic matter balance is positive or negative following different agronomic practices.”

As part of his work, Comeau will be measuring the amount of soil organic matter in soil samples collected at different locations and soil depths and at different times.

“Until now, studies in this region have only evaluated the amount of soil organic matter on a percentage basis without taking into account how much soil organic matter is at different depths in the soil,” he notes. “So part of my job will be to determine the amount of carbon per kilogram of soil per hectare, which is a much more solid estimation than just a percentage.”

One of the challenges in determining the effect of a specific agricultural practice on the amount of soil organic matter is that usually the year-to-year difference in organic matter is very small, so even things like sampling and equipment errors may mask the changes. “If we were to rely solely on soil organic matter data, it would normally take about 10 or 15 years before we could determine if a significant difference occurred due to a change in the management practice.”

So Comeau will also be measuring carbon inputs and losses, including carbon dioxide emissions from the soil. “I will measure the total amount of carbon going into the soil and the total amount going out of the soil at different times during the growing season. With those measurements, I can determine the annual carbon balance for the soil, instead of the 10-year balance that is currently determined.”

As part of his BMP studies, Comeau is leading a new project to find crop rotation options that will be good for the soil and for the grower’s bottom line.

“Currently in New Brunswick, farmers typically have a potato crop every two years in their rotations. They make most of their money in the potato years, so they produce a cash crop only once every two years. We will be testing different crop types and longer rotations that include pulses or other legumes. Based on similar studies on the Prairies, we’re hoping that the pulses will increase soil organic matter, while also providing another cash crop for growers.”

The field trials will be taking place at AAFC’s research farms at Harrington, P.E.I., and Fredericton. At each site, the following four crop rotation systems will be established and evaluated from 2018 to 2021: barley-wheat-potato; soybean-wheat-potato; fababean-wheat-potato; and pea-wheat-potato. Comeau will be working with Aaron Mills, a research scientist with AAFC in Charlottetown. Mills and his collaborators will mainly be looking at plant productivity, nitrogen-use-efficiency and other agronomic parameters, and Comeau will be assessing the effects of the rotations on the soil organic matter.

Comeau will also be involved in projects to assess cover crop options and compost practices in collaboration with agronomists and with Bernie Zebarth, an FRDC soil scientist, and studies to look at soil erosion impacts with FRDC research scientist Sheng Li. As well, Comeau hopes to work with industry agronomists in the coming years.

A big driver of soil organic matter loss in the region is the tillage, hilling and harvesting operations in potato production systems, so Comeau would like to work with agronomists and tillage specialists to evaluate different practices. He is also interested in looking into biochar, a carbon-rich soil amendment.

“Biochar is basically a charcoal that does not decompose into the soil, so it will remain there for hundreds or thousands of years,” he explains.

Researchers in Canada and other countries are examining biochar’s effects on such factors as crop yields, soil nutrient levels and carbon storage to reduce net greenhouse gas emissions.

As the new carbon expert on the FRDC team, Comeau is looking forward to helping develop the information that Maritime potato growers need for adopting BMPs that will increase their soil organic matter and their potato yields.

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