Words I didn’t expect to read in this week’s scientific paper: “The similarities in mass and contact area between modern agricultural vehicles and sauropods raise the question: What was the mechanistic effect these prehistoric animals had on Earth’s productivity?” The paper, from Thomas Keeler and Danny Orr, raises what may be a major concern: Agricultural compounds have grown over the past few decades, to the point where they can suppress underground soils where plant roots extend. This threatens agricultural productivity.
The paper then compares the compression threat to that posed by the largest animals that have ever roamed our lands: the sauropods.
Big crisis
We think the soil is dense, but the cracks and channels in the soil are essential for plant life, as they allow air and water to reach the roots. Soil compaction, in its extreme form, removes all this space, making the soil less suitable for plants. pressure is difficult to reverse; It takes decades of plant and animal activity to break down compacted soil again and rebuild healthy ecosystems.
There are many agricultural tools dedicated to plowing the land, destroying the soil and making it more permeable to air and water. But this device doesn’t reach all that depth. The “subsurface” area remains below the plowed soil, but below the surface remains within the area used by the roots of agricultural crops.
Obviously, having something heavy roll over the ground is an easy recipe for compacting it. Agricultural implements are also getting heavier, as larger tools become more efficient. In 1958, the weight of the combined harvester was usually around 4000 kg. Today, the average weight has increased to more than 35,000 kg. To avoid crushing the soil below this measure, the tires are made larger, and run at lower pressures, allowing the tires to spread over a wider area to reduce topsoil pressure.
But the force from the surface is translated down the surface in a smaller way depending on the area over which the pressure force spreads. On the other hand, at a certain depth, the stress is highly dependent on the mass of each wheel. Thus, increasing the combined mass (and other agricultural equipment) increases the risk of subsurface soil being subjected to compaction. This effect will be difficult to detect and correct, but can lead to loss of agricultural productivity.
global risk. Plus dinosaurs!
Compression risk is not evenly distributed. Drier areas have less groundwater pressure on them and are therefore less at risk of stress. Some countries also farm from small plots that do not take advantage of the efficiencies offered by large machines. However, many areas are at risk of compaction, including the eastern United States, eastern Australia, Argentina, and much of Europe. In general, this area corresponds to that suggested by a separate study to have lower productivity due to soil compaction. Overall, about 20 percent of critical agricultural areas are at risk.
Which brings us back to the dinosaur case. The sauropods became much larger than the largest harvesters – perhaps approaching 80,000 kilograms. The weight was distributed over only four ends, with a footprint nearly identical to that of modern tires (by contrast, reapers often had six tires). Finally, to move, sauropods had to lift at least one limb at a time. All of these factors combined meant that the sauropods had to put more pressure on the soil.
If current farm equipment poses a compression risk, dinosaurs almost certainly caused problems. But at the same time, animals of this size need a thriving ecosystem to support them. “The potential for significant soil compaction by foraging for sauropods does not appear to be compatible with productive land supporting regenerative vegetation to feed these prehistoric herbivores,” the researchers said.
How do we explain this apparent contradiction? Keeler and Orr, both specialists in agricultural studies, use an idea that has been popular with paleontologists for a while: Anything this size is almost semi-aquatic, as it will struggle to support its size. But rather than talking to paleontologists for more ideas, the authors simply state that “resolving this paradox is beyond the scope of this study.”
PNAS2022. DOI: 10.1073/pnas.2117699119pnas.org (About DOI).
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