Headers nearing the weight of biggest dinosaurs and that's a problem: study

A study led by Thomas Kelly and Dani Or, researchers from Sweden and Switzerland, found the total weight of laden combine harvesters has increased nearly 10-fold, from around 4000kg in 1958 to about 36,000kg in 2020, with wheel loads of the front axle increasing from 1500 to 12,500kg.

In comparison, the heaviest sauropod - a group that includes the brachiosaurus and brontosaurus - weighed 60,000 to 80,000kg.

Kelly and Or hypothesise that unconstrained roaming of sauropods, which were herbivores that relied on plants, would have had similar adverse effects on land productivity as modern farm vehicles.

The authors say a rapid evolution in farm machinery weight has been driven by an increase in power and capacity with wider cutter boards and larger grain tank capacity, aimed at improving harvest efficiency.

"Ironically, highly efficient tractors and harvesters may hamper progress toward increasing food production for a growing population under a changing climate due to the unintended risk of subsoil compaction," they write.

They say evidence from long-term field studies shows that subsoil compaction is difficult to reverse and can impair soil functioning for years to decades.

"These are manifested by a persistent decline in crop yields, limited water infiltration capacity, and a decline in other soil ecosystem services."

The researchers say that, based on a proposed subsoil compaction susceptibility index (SCSI) that integrates mechanisation levels and soil and climatic conditions, nearly 20pc of arable land is at risk for chronic sub-soil compaction in regions that are central for global food production.

"The fraction of arable land that is presently at high risk of subsoil compaction is about 20pc of global cropland area, concentrated in mechanised regions in Europe, North America, South America, and Australia," they state.

However, AgForce grains president Brendan Taylor said these days, most Australian growers kept compacted areas to a minimum.

"Most modern farming systems now with the GPS technology are working on a controlled traffic system (CTF) where all the machines run on the same wheel centres and same cutting width or planting width and spraying width so everything lines up so you've got your compaction in the same place, year in, year out," Mr Taylor said.

He did say that unseasonably heavy rainfall in parts of Australia last year did have some rethinking the size of their machines, though.

"The wet year last year did highlight that some of the machinery nowadays - particularly sprayers which are very big and carry big loads of water and are very heavy - didn't perform so well in the very wet conditions, whereas some of the older machines like the Spra Coupes that are quite small in stature and small in payload could actually tiptoe across the ground and not cause a lot of trouble.

"Whilst you might lose some of the efficiency of having a bigger machine, you could still operate when it was wet.

"There are a few people questioning, after what happened last year, that maybe having two smaller sprayers as opposed to one bigger sprayer [would be better] so that if it does get really wet, they're not pressing as hard on the ground."

The researchers then note that certain mechanised arid regions show considerably lower risk due to lower moisture and average higher soil strengths, such as the western US, south west Australia, Saudi Arabia, and southern Russia.

Despite a rapid increase in the number of tractors, most of Asia - including India and China - exhibits low SCSI values due to small farms that require small tractors, while values of the SCSI are low in sub-Saharan Africa because of low mechanisation levels.

"Nevertheless, trends in land aggregation in these regions and the emergence of business models for provision of services using larger agricultural vehicles may drive the SCSI toward values presently found in high-income countries," they say.

Kelly and Or say their study provides evidence that present trends of increasing agricultural vehicle weights are not sustainable, necessitating consideration of subsoil critical stresses in future designs to supplement the present focus on traction and contact stress.

"Sub-soil stresses induced by today's agricultural vehicles have reached or crossed critical levels for ecological functioning of subsoil root zones, with adverse consequences for land productivity," they write.

"Considering the narrow range of mechanical limits of most soils in temperate regions, future agricultural vehicles must be designed with intrinsic soil mechanical limits in mind to avoid chronic soil compaction."

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