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Potato growers in Canada are grappling with the challenge of reducing reliance on commercial fertilizer amid rising costs and environmental concerns. Experts emphasize that while fertilizers have historically boosted agricultural productivity, they can also lead to yield declines and environmental degradation if mismanaged. Judith Nyiraneza, a research scientist with Agriculture and Agri-Food Canada (AAFC), highlights the importance of soil health, stating that healthy soils can provide essential nutrients without solely depending on fertilizers.

Key strategies include:

• Incorporating organic amendments to enhance soil structure.
• Implementing crop rotation and cover cropping to improve nutrient retention.
• Adopting precision agriculture technologies for efficient nutrient management.

This issue is critical for Canadian farmers as they seek sustainable practices that maintain crop yields while minimizing environmental impact, ultimately supporting food security and economic viability in the agricultural sector.

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By any measure, fertilizer has been one of the great success stories of modern agriculture. However, it can also be one of its biggest headaches. As prices rise and environmental scrutiny tightens, potato growers across Canada are asking a hard question: How far can we reduce our reliance on commercial fertilizer without sacrificing yield, quality or profitability?

The fertilizer paradox: Indispensable, but imperfect
There is no getting around it—commercial fertilizer helped build modern potato farming. “The increase in agricultural productivity was possible due to the development and mass production of chemical fertilizers, the introduction of modern agriculture [and] high-yielding varieties, and use of other inputs, including pesticides,” says Judith Nyiraneza, research scientist with Agriculture and Agri-Food Canada (AAFC).

Nyiraneza stresses that the soil organic matter is an important source of crop nutrients. Fertilizer provides supplemental nutrition to the plants, “And in most cases, the proportion of nutrients derived from the soil is higher than from fertilizers.”

In other words, a significant share of plant nutrients still comes from the soil itself—specifically organic matter and mineral reserves. Fertilizer supplements that supply, but it does not replace it.

The downside of using fertilizer can’t be ignored, however. Cost is a major factor as fertilizer prices have swung wildly in recent years, driven by energy costs, geopolitics, and supply-chain disruptions.

Environmental losses and diminishing returns are other key concerns. According to Nyiraneza, “Application of lower amounts of fertilizer than the plant requires can lead to yield decline, but applying higher than the optimum can affect the quality of the crops [reduce the nutritional content of foods], represent an unneeded extra production cost for producers, and negatively impact the air and water quality.”

Scott Anderson, science coordinator at the Charlottetown Research Centre with AAFC says historically, “Fertilizer has been a pretty cheap form of insurance,” since it gave growers steady yields, regardless of the growing conditions or management practices. “That’s why we’ve seen a consistent use of fertilizer for potato production,” he says.

Feeding the soil, not just the crop
Reducing reliance on commercial fertilizer boils down to a key principle: Feed the soil first, so the soil can feed the crop.

“Unhealthy soils, such as a compacted soil, can show deficiency of nutrients even when they are applied in sufficient amounts,” says Nyiraneza. “Beneficial management practices to increase soil organic matter will allow better soil aeration, soil infiltration and drainage, and ability to hold nutrient and water.”

Scott Anderson (left) and Roger Henry (right) grade the plowdown challenge potatoes at the Charlottetown Research and Development Centre. Image: Agriculture and Agri-Food Canada

Studies demonstrate that crop productivity was increased by integrating organic and inorganic nutrient sources, adds Nyiraneza. Soils rich in organic matter behave like nutrient banks. They hold water longer, improve aeration and root growth, and support microbial communities that slowly release nutrients in plant-available forms.

“Finally, efficient weed, pest and disease management programs are crucial to sustaining crop productivity,” says Nyiraneza.

The above-mentioned practices will improve soil health, which has a more important effect on plant growth than their fertilizer value, Nyiraneza explains. “The soil structure controls the nutrients, water and air movement, while providing a habitat for microbes and supporting root growth,” she says.

Growing potatoes without commercial fertilizer
Is it possible to grow potatoes without using any commercial fertilizer whatsoever? The short answer is yes, sometimes, on some fields — but it’s risky.

“Depending on the farm, the risk may be that the plants will not grow to their maximum potential, and thus yield will decline in certain fields, with even greater consequences if the practice continues over time.”

Studies show 30 to 50 per cent of crop yield is attributed to synthetic fertilizers. Remove them entirely, and yield losses are likely, unless soils have exceptionally high nutrient-supplying capacity. “Each farm is different,” she says. “In certain fields, the soil is the main source of nutrients, while in others, the fertilizer is the main source.”

In other words, if the soil already has a high nutrient supply capacity, Nyiraneza argues that it is possible to supplement crop nutrition with animal waste and green manure, rather than commercial fertilizer. “The benefits would enhance the nutritional content of foods, and growers can save money that would otherwise be spent on purchasing and transporting commercial fertilizers,” she says.

Replacing commercial fertilizer with organic options
One of the benefits of commercial fertilizer is that it can be applied when it’s actually needed. Organic fertilizer from plants or animal materials, on the other hand, need to be broken down into forms that can be used by plants, and may not be synchronized with the plant demand, or be available in sufficient amounts, Nyiraneza explains.

“Organic fertilizer applied in excess or improperly can also be responsible for environmental degradation similarly to synthetic fertilizer,” she says. “Replacing commercial fertilizer with organic fertilizer can result in yield decline, unless the soil nutrient supply capacity is enough to satisfy crop nutrient demand.”

Some organic amendments, she adds, are a reliable source of nutrients (i.e. liquid manure), others are beneficial in improving soil structure, and have lower fertilizer value (i.e. compost). “It is Important to know the soil status and the benefits of an implemented management practice,” she says.

According to Marisol Quintanilla, associate professor and nematologist at Michigan State University, manure offers other benefits too. “Manure,” she says, “Especially poultry manure, has been very effective at killing nematodes, while also providing nutrients and micronutrients.”

Quintanilla explains growers need to be careful regardless of whether they’re using manure or commercial fertilizer, since both can contaminate the environment if not properly applied or if misused. “Manure isn’t foolproof,” she says, “But the benefit is that you’re recycling nutrients, and you’re adding organic matter for beneficial organisms.”

Quintanilla notes the nitrogen from commercial fertilizer can be lost to the water table or into the air.

Conversely, the nutrients in manure and compost are more stable. “The nutrients are not as concentrated, and you will still lose some, but less that you would with commercial fertilizer,” she says.

Best practices that consistently pay off
While commercial fertilizer may be a quick solution, it is possible to cut down by adopting best practices and planning accordingly.

Nyiraneza lists the following beneficial management practices: organic amendment incorporation, reducing the intensity and frequency of soil tillage, adopting long and diversified rotations (if possible), and minimizing the time the soil is left bare by maintaining live plant roots as long as possible.

She explains that these practices will enhance beneficial soil microorganisms, soil structure and nutrient use efficiency, as well as the soil’s ability to supply nutrients.

“Following local nutrient recommendations and applying the four ‘R’ principles will increase nutrient use efficiency,” says Nyiraneza. “Studies have demonstrated that the synchrony between N released from fertilizers and the plant peak N demand was enhanced by split-N fertilizer application and the use of enhanced N fertilizers resulting in increased yield and reduced N losses.”

Beneficial management practices
While beneficial management practices can increase agricultural resiliency, boost productivity, and reduce the impact on the environment, Nyiraneza warns that they are also context-dependent. In other words, fertilizer is not a one-size-fits-all solution.

“Certain regions follow a two-year potato rotation, while others follow a three-year rotation,” she says. “Eastern Canada is characterized by high rainfall and sandy loam soils with low soil organic matter. The focus is on reducing soil erosion with winter cover cropping and nurse crops. The climate is drier in western Canada, and the soils are high in soil organic matter. Growers put emphasis on conservation tillage to manage soil moisture, and rely on irrigation for certain cash crops.”

In addition, certain farms focus on producing early maturing potato varieties that require less nutrients than would be required by late-maturing varieties. “Early maturing varieties can be harvested earlier to allow seeding winter cover crops, which reduce soil erosion and take up residual soil nutrients after potato harvest,” says Nyiraneza .

Moreover, while certain farms are rain-fed, others are irrigated, which means growers can apply nutrients with irrigation to increase their efficiency, Nyiraneza explains. “Certain farms have adopted precision agriculture technologies in managing water and nutrients, while others do not have access to the needed tools. These differences will impact the amount of fertilizer applied, their use efficiencies, as well as maximum yields.”

Michigan State University’s Quintanilla says that nutrient management is paramount. “Cover crops, for example, can prevent erosion while the roots and the plant biomass hold on to some of the nutrients,” she say. “You’ll never be able to hold on to all the nutrients. You’ll always lose some. But the goal is to lose less.”

Choosing the right cover crop is key. “A lot of the brassica, especially oilseed radishes, tend to be beneficial,” she says. “They are effective at reducing nematode diseases, and they hold nutrients pretty well during the winter season. They grow well in the cold season, and in the spring, the residue is very easy to deal with. It’s not very fibrous, which makes it easier on your tillage equipment.”

Agriculture Canada’s Anderson says that his research, including the well-known Plowdown Challenge, proves that a properly managed cover crop rotation can significantly boost nutrient levels in the soil.

“Carefully managing when you plow and what you plow can add a lot of nitrogen to your soil,” he says. “And if you manage it well, it will grow the supply of nitrogen in your soil, and that will help you reduce your reliance on fertilizer.”

That said, Anderson is quick to point out that he’s not recommending eliminating fertilizer altogether.

“Agronomy is still agronomy,” he says. “You’re going to need your N, P and K from somewhere. Inorganic fertilizer is readily available, and I’m a firm believer that if you manage it properly, it’s not an issue.”

Cover crop options and crop rotation schedules
Claudia Goyer, research scientist with AAFC has been conducting studies with McCain at the “Farm of the Future.” She has been looking at cover crop options and crop rotation timing. More specifically, she is comparing two-year crop rotation cycles with three-year cycles, and looking at the advantage of using a diverse mix of plants for the cover crops.

Goyer says that soil tends to react quickly to a diversity of plant matter. Although all the data isn’t available yet, she concludes that the three-year cycle is better than a two-year cycle because it results in less damage from pathogens, and it gives growers a better yield overall. “If you can go even longer for your crop rotation, you’ll be controlling disease even better,” she says. Another important benefit: “Although the green manure is adding more plant residue and nitrogen content, it’s also helping with the soil moisture content,” she says, “and it’s really helping make the soil more resilient.”

Her team employed a “multi-mix” approach when considering cover crop options, with either three or six plant species planted together (including clover, alfalfa, rye grass and others) on a plot of land. The right mix of plants, she says, depends on the growing conditions in your local area, noting that it takes a bit of trial and error to get it right. “We saw an improvement in yield with a multi-mix approach,” she says,.

While experts aren’t suggesting growers completely eliminate the use of commercial fertilizer, it is possible to reduce reliance on it. The research is clear: Healthier soils supply more nutrients, lose less to the environment, and make every pound of fertilizer work harder. Feed the biology first, fine-tune fertilizer to fill the gaps, and you’ll spend less on inputs, face less risk, and set your farm up for long-term resilience.