The agricultural lands of the Montérégie devoted to the cultivation of corn are suffocating. Compacted by tractors for decades, these soils are becoming increasingly inhospitable to plants. So much so that, within 20 years, the profitability of farms could evaporate.
These are the results – “a strong trend” – that will be presented this Thursday by Jean Caron, professor at Laval University, holder of the Chair for research in the conservation and restoration of organic soils, on the occasion of the 90e Acfas congress.
This analysis, exposed in recent months to agricultural producers themselves, is a “breakthrough discovery”, according to Mr. Caron, which should encourage Quebec society to cherish the health of its soils to avoid wasting one of its most great riches.
Soils that are too compact are detrimental to plant growth. The roots cannot access the oxygen they need. They also have difficulty breaking through the ground. Lack of air also forces soil microbes to “breathe” with nitrogen rather than oxygen, which decreases the availability of nitrogen fertilizers for plants.
At the request of concerned farmers, Mr. Caron has conducted in recent years a study on the health of the soils of 20 sites in Montérégie. These agricultural lands are devoted to field crops: corn, soybeans and wheat. The agronomy professor’s team took hundreds of samples there during the summers of 2019, 2021 and 2022.
Conventionally, agronomists measure soil density to assess whether or not it is too compact. This approach, however, does not take into account the connectivity of the asperities in the soil, an essential condition for the air to be able to reach the roots.
In the laboratory, Mr. Caron and his collaborators therefore measured the density of the soil samples, but also the relative diffusivity of the gases. This indicator gives a better idea of the interconnection of pores in the soil. The results are unequivocal, according to the researcher: the floors are suffocating.
In 90% of the samples, the air diffuses with such difficulty that the roots of the plant will lack oxygen. And 40% of the soils are so compact that they are affected by water drainage problems. (These results have not yet been peer reviewed.)
In addition, Dr. Caron detects a correlation between soil compaction — measured by the diffusivity of gases — and corn yields. This relationship holds for several years, different soil types, different production schedules. “It’s really a basic mechanism that acts, he says. I have rarely seen data like this in my career as a researcher. »
And the phenomenon is not about to be reversed. “If your soil gets denser, you will need a bigger tractor, which will use more energy, to plow the soil. And the fertilizer bill will also increase, because the nitrogen will be less and less effective. Gross income will decrease, and net expenses will increase. »
The professor predicts that if the compaction trend continues, it will no longer be profitable to grow corn on these Montérégie lands within twenty years. Over 60% of Quebec’s field crops are found in this region.
From horse to tractor
Soil compaction — a global problem, but particularly acute in North America, where the machinery is very heavy — will also tend to increase greenhouse gas (GHG) emissions from the agricultural sector, as it will denitrification.
Denitrification is the respiration of nitrogen by soil microbes. This process releases nitrous oxide (N2O), a very powerful GHG that accounts for about 5% of Quebec’s emissions. The government also wants to reduce the use of nitrogen fertilizers by 15% by 2030.
However, Mr. Caron’s results suggest that due to the lack of oxygen in the soil, the appetite of microbes for nitrogen fertilizers will increase. Given this competition, for the same amount of fertilizer applied, the boost to the plants will be less, and the emissions of N2O, superior.
Since draft horses gave way to tractors, around the middle of the 20e century, soil compaction is spreading deeper and deeper into cultivated land. Plowing up to 80 centimeters deep could solve the problem, but would involve a prohibitive cost.
Other solutions exist, explains Professor Caron. Rotate with plants with deeper root systems. Choose much lighter tractors. Develop drainage plans more systematically. Plant trees in certain strategic places.
In short, the problem must be tackled, one bite at a time. Instead of buying more chemical fertilizers, “we could promote soil health,” suggests Mr. Caron.