What’s worse for the soil?

Words I didn’t expect to read in this week’s scientific article: “The similarity in mass and contact area between modern agricultural vehicles and sauropods begs the question: What was the mechanistic effect of these prehistoric animals on Earth’s productivity?” The article, by Thomas Keeler and Danny Orr, raises a potentially major concern: Agricultural compounds have grown in recent decades to the point that they can compress the underground soil where crop roots extend. This poses a threat to agricultural productivity.

The paper then compares the threat of compression to that of the largest animal to ever roam our country: sauropods.

The Great Crisis

We think the soil is firm, but the holes and channels in the soil are essential to plant life as they allow air and water to reach the roots. Soil compaction, in its extreme form, takes away all these spaces, making the land less suitable for plants. pressure is difficult to reverse; It can take decades of plant and animal activity to break down compacted soil and restore a healthy ecosystem.

There are many agricultural machines that are intended for plowing the soil, breaking the soil and improving the passage of air and water. But this device doesn’t go that deep. The “underground” area remains below the plowed soil, but below the surface it remains well within the area used by the roots of agricultural crops.

Obviously, it’s easy to roll something heavy on the ground to compact it. Agricultural equipment is also becoming increasingly heavier, because larger equipment has become more efficient. In 1958 the weight of a typical combine was about 4000 kg. Today, this average weight has grown to over 35,000 kg. To avoid crushing soil below this size, tires are made larger and run at a lower pressure, which allows the tire to spread over a larger area to reduce pressure in the topsoil.

But forces from the surface translate to a lesser extent below the surface, depending on the area in which the compressive force spreads. Instead, the stresses at some depths are highly dependent on the mass of each wheel. As such, the increased mass of combines (and other farm equipment) increases the risk of the subsoil being exposed to compaction. This effect will be difficult to detect and correct, but it can lead to a loss of agricultural productivity.

global risks. Plus the dinosaurs!

Compression risks are not evenly distributed. Dry regions have less groundwater pressure and therefore run less risk of overpressure. Some countries also grow on small plots that do not take advantage of the efficiency of large machines. However, many areas are at risk of compaction, including the eastern United States, eastern Australia, Argentina and much of Europe. Overall, these areas are in good agreement with those suggested in a separate study to have lower productivity due to soil compaction. In total, about 20 percent of important agricultural areas are at risk.

Which brings us back to the case of dinosaurs. Sauropods grew much larger than even the largest harvesters—perhaps nearly 80,000 kilograms. Their weight was only distributed over four ends, with footprints nearly identical to those of modern tires (graapers, on the other hand, often have six tires). Finally, in order to move, the sauropod had to lift at least one limb at a time. All these factors combined meant that sauropods had to exert more pressure on the bottom.

Now if farming equipment posed a risk of compression, dinosaurs were almost certainly causing problems. But at the same time, animals of this size would have needed a thriving ecosystem to support them. “The potential for significant soil compaction by foraging for sauropods seems incompatible with the productive soils that supported regenerative vegetation to feed these prehistoric herbivores,” the researchers say.

How do we explain this apparent contradiction? Keeler and Orr, both specialists in agricultural studies, resorted to an idea that had been popular in paleontological circles for a while: Anything this size was almost semi-aquatic, as it would struggle to support its size. But instead of talking to the paleontologist for more ideas, the authors simply stated that “solving this paradox is beyond the scope of this study.”

PNAS2022. DOI: 10.1073/pnas.2117699119pnas.org (Over DOI’s).

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