Fertile land for growing vegetables is at risk — but a scientific discovery could turn the tide

A large proportion of the vegetables consumed in Québec are grown in the Montérégie region in what are known as organic soils. Highly fertile and rich in organic matter, these soils are particularly well suited to vegetable production.

Yet many farmers are now raising concerns about the rapid degradation of these soils over the last few years. This is happening so quickly they could potentially disappear in a period of 50 years.

This situation, which is unfolding worldwide, is alarming. Organic soils are among the pillars of food self-sufficiency in Québec, as elsewhere, and are essential to producing the vegetables that we eat every day. So it is crucial to stop their degradation.

Fortunately, our research work at Laval University’s Faculty of Agricultural and Food Sciences, carried out in partnership with 14 vegetable farms, offers a glimmer of hope for ensuring the sustainability of these soils.

Degradation by the forces of nature

Organic soils are characterized by their high content of organic matter, which ranges from 30 per cent to almost 100 per cent. They consist mainly of plant residues, similar to compost, and are formed in peatlands, where the soil is gorged with water. High water content prevents oxygen from entering the soil and slowing down the decomposition of hydrophilic plant residues that accumulate over time.

The first essential step in cultivating these soils is drainage, i.e. removing the water from the soil. At this point, oxygen is introduced, an essential element for plant growth. However, the entry of oxygen accelerates the activity of soil microorganisms, which in turn, breaks down the accumulated organic matter. Organic soil carbon, the main constituent of organic matter, is then transformed into CO₂ (carbon dioxide), which is dissipated into the air. The accumulated organic matter gradually disappears as a result. This microbial decomposition leads to the loss of around one centimetre of organic soil per year.

In addition to soil loss, decomposition by microbes also alters the quality of soil. Soil that is initially composed of plant fibres is gradually transformed into fine, ash-like particles. This finer material causes the soil to become more compact and less aerated, which slows down water and air exchange essential to the growth of agricultural plants. These fine particles are also easily carried away by the wind, accelerating soil loss.

At the present time almost 16 per cent of the land area of cultivated organic soil in Québec’s Montérégie region is already considered thin and highly degraded due to heavy decomposition. This is an alarming finding for the future of vegetable production, especially if this proportion increases.

The region’s farmers, the first to witness this degradation, are looking for solutions to protect their land.

A nature-based solution

In the past, the main method recommended for conserving organic soils was applying copper to slow down the decomposition by microbes. Copper can inhibit the activity of enzymes produced by microorganisms, which is like slowing down their digestive system.

However, our work revealed that this approach was not very effective. The method also poses a risk of environmental contamination due to the potential dispersion of copper in natural environments.

The new approach we propose is based on the natural principle of photosynthesis. Through this process, plants use energy from the sun and CO₂ from the air to produce plant tissue. Plants then transform the CO₂ in the air into organic carbon, the main constituent of organic matter. This process is, therefore, the opposite of decomposition.

Straw and wood are particularly rich in organic matter and organic carbon. That’s why we’ve decided to concentrate on using these materials, which are produced on land of low fertility, harvested and then applied to organic soils to add carbon.

Straw and wood to the rescue

Our research has shown that applying straw or wood chips to organic soils can compensate for the carbon and soil losses caused by microbial decomposition. What’s more, when mixed with soil in appropriate doses, straw and wood chips have the potential to restore the soil aeration and drainage that are essential for good vegetable growth.

However, as the addition of new organic matter to the soil stimulates microbial activity, doses must be adjusted to avoid creating too much competition between plants and soil microbes for certain essential elements, such as nitrogen. So it is important to apply the appropriate doses to maintain a balance between the needs of the soil microbes and of the plants.

As a result, this practice holds the potential to regenerate cultivated organic soils and improve the climatic footprint of vegetables in Québec and elsewhere.

In parallel, we have also explored the use of polyphenols in slowing down decomposition. These molecules, produced by plants, are known to slow down the activity of degradative enzymes in natural organic soils, but their use for cultivated organic soils had not been studied. This approach has shown promising potential but requires further study before it can be applied on a large scale. For the time being, our studies have been limited to a small number of soils, which does not allow us to generalize the conclusions on a large scale.

Our team is also carrying out work on wind erosion and drainage to enable the conservation and restoration of these central soils in vegetable production.

Mobilizing the farming community

Aware of the urgent need to take action to save their soils, farmers have already begun applying straw and wood chips to their land to preserve this limited and fragile resource for future generations. They have also joined together to take part in another research program, from 2024 to 2029, which will work to optimize this solution.

This initiative has gained the attention of international farmers and researchers who have come from England, Belgium, Finland and Sweden to visit the Québec farms where this new practice has been adopted.

The degradation of cultivated organic soils is a worldwide phenomenon that threatens to wipe out many highly fertile agricultural production areas. So it is important to take an interest and act quickly.