Big tractors, now heavier than many dinosaurs, can damage deep soil

A farm tractor is taller than an elephant. A combine harvester weighs up to 36 tons and is fully loaded with grain. As these mechanical beasts lumber across fields, their heavy weight can cause soil to be crushed and make it harder for plant roots to grow. A new study suggests that such effects could diminish harvests across 20% of global cropland in the coming decades.

A soil scientist at Ohio State University says heavy machinery can cause damage.

The largest tractor is almost 10 times larger than it was in the 1960s. The sauropod dinosaurs are the largest creatures ever to walk on land. All that extra weight comes at a cost.

To find out how agricultural vehicles have changed and how they might affect the soil, Thomas Keller of the Swedish University of Agricultural Sciences and Dani Or of the Desert Research Institute assembled published industry data. They modeled the forces that the tires exert on the soil.

In mechanized farming, the upper soil has long been the site of compaction. On many farms, the ground is prepared for planting by plowing or tilling the soil each season. Researchers say that the problem is deeper because the layers below 50 centimeters often exceed safe limits.

Less water and air can reach the deep soil if the squeezing collapses the tiny spaces between soil particles. The changes could decrease crop yields by 10% to 20%. It could take decades for organisms to loosen the deep soil.

It is not just combine harvesters. Vehicles used for logging and other farm equipment are getting heavier. Around 20% of agricultural land around the world is at high risk of lower yields from deep soil compaction, according to a report today in the Proceedings of the National Academy of Sciences. These areas, like the savanna of Brazil and southeastern Australia, have vulnerable soil and heavy equipment, and they are the bread baskets of the world.

Thomas Way is an agricultural engineer with the U.S. Department of Agriculture. When fields are wet, soil is more vulnerable. During dry weather, gps can help farmers drive the same routes to reduce the area under pressure.

The new study raises the question of what happened when sauropod dinosaurs were on Earth. The researchers theorize that they may have waded in the water along the shoreline. Modern farm machines need to be designed with an eye toward soil strength, otherwise they will go the way of the dinosaurs.