In fact, the weight of combine harvesters has increased almost tenfold in the last sixty years, from around 4 to 36 tons, as Thomas Keller from Agroscope and the Swedish University of Agricultural Sciences in Uppsala notes with his colleague Dani Or from ETH Zurich.
But contrary to what might have been assumed, this had hardly any effect on the load on the soil surface – it remained largely the same. This is due to the tires being wider at the same time, which distribute the weight of the machine evenly.
Only: The load in the subsoil, i.e. in the root zone of the plants, increased steadily. In arable farming, that layer is called the subsoil that is not constantly exposed to direct mechanical intervention.
As the researchers note, long-term field studies show that subsoil compaction is difficult to reverse and can affect soil function for years to decades. According to the study, almost 20 percent of arable land in regions that are of central importance for global food production is threatened by “chronic subsoil compaction”.
The weight of modern agricultural machinery far exceeds the weight of the heaviest living land animal – the African bush elephant. In fact, the machines will soon weigh as much as the heaviest animals that have ever walked the earth: the sauropods. These were among the most species-rich and widespread groups of herbivorous dinosaurs.
This raises the question of what mechanical impact these now-extinct creatures might have had on land productivity, the researchers said. They calculate that the mass to be carried by each foot of a sauropod when moving was 20 tons or more. By way of comparison, a modern sugar beet harvester weighs 60 tons when fully loaded, but is fitted with three axles and six tires, which amounts to around 10 tons per wheel.
The potential for significant soil compaction by the dinosaurs seems inconsistent with productive land, Keller and Or write. And yet the plant life seemed lush enough to provide the giant lizards with enough food.
Although the authors emphasize that resolving this paradox is beyond the scope of the present study, they do offer some ideas. According to this, it would be possible that the sauropods did not just roam freely through the landscape, but along already well-compacted paths, and only left them to graze. “Free foraging in the landscape seems unlikely due to the risk of massive soil compaction and loss of productivity,” they conclude.
While the dinosaurs appear to have found a solution to the compaction problem, the ongoing trend toward ever heavier agricultural machinery is unsustainable, according to the researchers. It is important to consider the critical loads on the subfloor in future constructions.