A farmer watching the Case tractor equipped with Michelin tires with a wide footprint shook his head when he saw them turn down two more knives, so that they would try to pull a nine-knife ripper plow with a 330 –horsepower, front-wheel assist tractor.
"That's just not enough tractor for that big a pull," the farmer mused. "That ground is tough. They took silage off of here and created compaction by driving on it with full silage wagons."
As it turned out, the farmer was right. When the operator, Case expert Roger Lewno, tried to start out at the same speed he ran the seven-shank, the tractor balked. So he geared down and pulled it. But on the clay hill where organic matter is lower, he reported more tire slippage than he would like. The tires were biting in great, but the pull was just too great for the horsepower. They were running the machine about 12 inches deep.
One solution would be to run a couple inches shallower, if your soil compaction or plow layer pan was shallow enough o still allow that to shatter when soils are dry. But probably the better option would be to stay with the smaller machine, still a big load to pull in those conditions at seven shanks, or go to a bigger tractor if you insisted on needing a nine-shank machine.
At some point, horsepower will become limiting, not the tires, he noted.
Tony Vyn, a Purdue University agronomist, checked soil compaction with a penetrometer after the ripper passed. He made it plain up front that using the penetrometer in a demonstration like this was 'playing around on a sunny day," certainly not research. Nevertheless, he pointed out that the ripper was lowering compaction readings between the shanks. That's the object, he says. Right behind where a shank runs, the penetrometer won't show much resistance at all. What counts is what is going on between the shanks. That is what you want to shatter.
That was being achieved, Vyn noted. The drier the soils when you rip ground, the more likely the odds that you will break up underground compacted layers and shatter them as you want to do. That's not likely to happen if the soil is wet, or even 'tacky,' as some like to call it.