Jury still out on benefits of deep ripping

There has been a host of studies on whether deep ripping can fix soil compaction but the results have been inconclusive

Does deep ripping fix soil compaction and improve yields?

Despite numerous studies, no one really knows, attendees at the recent Special Crops Symposium in Brandon were told.

“Collectively, we haven’t done enough disciplined testing or research yet to sort out whether or not it is profitable in Manitoba,” said John Heard, soil fertility specialist with Manitoba Agriculture, Food and Rural Initiatives.

Manitoba research, from the 1980s up to 2010, has been inconclusive, he said. A major Iowa study in 2004 showed the yield response to measures taken to address soil compaction varied widely, from a loss of up to six bushels of yield with corn to a 12-bushel advantage. That study tested a John Deere 2100 minimum-till inline ripper set to a 16-inch depth on more than 100 replicated strip trials. The overall average was just 1.4 additional bushels of corn per acre, which didn’t cover the estimated cost of $15 to $20 per acre for doing the work.

“These were all farms that obviously thought they had a problem,” Heard noted.

The study’s authors concluded that lower, heavier-textured soils benefited most from deep ripping in the fall, and the most profitable yield response occurred where a problem had been identified, such as in field headlands.

One downside was the ripper’s tendency to bring stones to the surface, and one grower reported having to replace a ripper shank shear bolt after, on average, every pass.

Generally, soil compaction isn’t a major problem in Manitoba due to the freezing and thawing action that breaks up packed soil particles during the winter. But it can happen, as evidenced by the experience of one farmer whose practices resembled a “how-to” list of ways to induce soil compaction.

The field which Heard visited in 2011 was the first such case he had seen in his career outside of Ontario. It had been continuously cropped for corn silage and was always planted early when the soil was wet. Also, manure from the farm’s livestock was spread under damp conditions in the fall by a spreader that didn’t have flotation tires.

Even though the field had been heavily manured, the crop showed signs of nitrogen, phosphorus and potassium deficiencies — which had the farmer suspecting his fertilizer company had shorted him. In fact, the deficiencies occurred because the roots were forced to grow between cracks in the hard soil clods.

“The plant is really our indicator of whether we’ve got soil compaction,” said Heard, adding visible potash deficiency is one strong indicator, especially in corn when “firing” is seen on the bottom leaves.

Depending on the severity of compaction, it can take a very long time for Mother Nature to repair the damage. In Minnesota, for example, ruts from pioneer wagon trains are still evident even after 140 years.

The freeze-thaw effect works, but it depends on how many cycles occur over a winter, said Heard. Heavy snow cover can mitigate fluctuations in temperature.

“Sometimes with a good snow pack soil temperatures can even warm up from below,” said Heard.

Obviously, the best way to prevent compaction is to only till when the soil is dry enough to support the equipment’s weight. And that means more than simply being able to drive on the field without getting stuck, Heard said.

Take a tip from Grandpa to judge whether the soil is “fit to be worked,” he said. Dig down to tillage depth, take a lump of soil and squeeze it into a ball. If, when dropped, it crumbles, then that means you’re good to go.

“But if the ball stays intact, or the soil surface is so wet that it cushions it, then it’s time to go home and change the oil in the tractor instead,” said Heard.

Staying in the same tracks each time when moving heavy machinery over a field is better than trying to spread out the impact, he added, because 80 per cent of the “hurt” takes place on the first pass.

Other measures such as not overusing ballast, and maintaining tires at rated pressures can also mitigate compaction.

Studies using a penetrometer found that there is little difference in effective soil porosity between properly inflated duals and tracks at various depths. But when duals are overinflated, over 90 per cent of the pore spaces in the soil can be lost from a single pass under wet conditions.

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