Which is worse for the soil: combines or dinosaurs?

Enlarge / Having this guy trampled could mean things would struggle to develop there later on.

Words I didn’t expect to read in a scientific article this week: “The similarity in mass and contact surface between modern agricultural vehicles and sauropods raises the question: what was the mechanical impact of these animals prehistoric data on land productivity? The article, by Thomas Keller and Dani Or, raises what could be a significant concern: agricultural vehicles have grown in recent decades, to the point of compacting the ground underground where the roots of crops extend. This poses a risk to agricultural productivity.

The article then compares this risk of compaction to that posed by the largest animals that have ever roamed our lands: sauropods.

The great crisis

We think soil is strong, but gaps and channels in the soil are essential for plant life because they allow air and water to reach the roots. Soil compaction, in its extreme form, removes all of these spaces, making the soil much less hospitable to plants. And the compaction is hard to reverse; it can take decades of plant and animal activity to break up the compacted soil again and restore a healthy ecosystem.

There is a lot of agricultural equipment dedicated to tilling the soil, breaking it up and making it more air and water permeable. But this material does not go down so deep. A “subterranean” area remains under the plowed soil, but the subsoil is still well within the area used by the roots of agricultural plants.

Obviously, rolling something heavy on the ground is an easy recipe for compacting it. And farm equipment is getting heavier and heavier because bigger equipment is more efficient. In 1958, a typical combine harvester weighed around 4,000 kg. Today, this average weight has increased to more than 35,000 kg. To avoid crushing the soil under this mass, the tires have become larger and run at lower pressures, allowing the tire to spread over a larger area to limit surface soil compaction.

But the forces from the surface translate down to the subsoil in a way that is less dependent on the area over which the compressive force is distributed. Instead, at certain depths the stresses are largely dependent on the mass per wheel. Thus, the increasing mass of combines (and other agricultural equipment) increases the risk of subsoil compaction. This effect will be difficult to detect and correct, but it can lead to loss of agricultural productivity.

Global risks. And the dinosaurs!

The risks of compaction are not evenly distributed. Drier regions have less groundwater to expel and are therefore less at risk of compaction. Some countries are also cultivating via smaller batches which do not benefit from the efficiency provided by large equipment. Yet many regions are at risk of compaction, including the eastern United States, eastern Australia, Argentina and much of Europe. In general, these areas correspond well with those which, according to a separate study, suffer from a decline in productivity due to soil compaction. Overall, about 20 percent of important agricultural areas are threatened.

Which brings us back to the question of dinosaurs. Sauropods became considerably more massive than even the largest harvesters – they may have approached 80,000 kg. Their weight was distributed over just four limbs, with footprints roughly comparable to those of modern tires (harvesters, on the other hand, often have six tires). Finally, to move, sauropods had to lift at least one limb at a time. All of these factors combined mean that the sauropods should have exerted much more pressure on the ground.

If farm equipment now poses a risk of compaction, dinosaurs almost certainly caused problems. At the same time, however, animals of this size needed a thriving ecosystem to support them. “The potential for heavy soil compaction by foraging sauropods appears incompatible with productive land that supported renewable vegetation to feed these prehistoric herbivores,” the researchers said.

How can this apparent contradiction be explained? Keller and Or, both specializing in agricultural studies, have been embracing an idea popular in paleontology circles for some time: anything this large was almost certainly semi-aquatic, as it would struggle to support its mass. . But rather than speak to a paleontologist for more information, the authors simply state that “resolving this paradox is beyond the scope of this study.”

PNAS2022. DOI: 10.1073/pnas.2117699119pnas.org (About DOIs).

#worse #soil #combines #dinosaurs

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