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Corn+Soybean Digest

To Till Or Not To Till

Listen to a conversation about tillage practices and you might think it's a discussion about religious affiliation. Nearly gone are the days of turning over massive furrows of soil with moldboard plows, but the discussions about tillage haven't disappeared — or gotten less emotional.

“We can argue about fertilizer rates, color of paint — a lot of different topics, but when it comes to tillage, it hits a nerve,” says Tracy Blackmer, director of research at the Iowa Soybean Association (ISA). “Tillage is a major investment and people are doing what they think is right.”

ISA's On-Farm Network has just completed its second year of tillage trials. Farmers participating in the studies compared their current tillage system to deep tillage in side-by-side strips.

“The programs we're directing start with the notion that most people can find something to improve,” says Blackmer. “The question is how you identify that opportunity. What we emphasize is not so much the practice itself, but how growers can evaluate alternative practices accurately.”

He adds that ISA focuses on the method, not the answer, which is why the association assists its members with establishing on-farm strip trials, as opposed to comparing farm-to-farm results.

“We typically don't like to make field-to-field comparisons because other variables change, including genetics, planting date, past management history and different rain patterns,” says Blackmer. “Any one of those factors can affect yield. So if we compared the yield between two fields, we wouldn't be able to say the differences were caused by tillage. By putting multiple strips in the same field it's easier to attribute yield differences to the practice you're evaluating.”

In general, the ISA on-farm tillage studies have found no consistent yield benefits from deep tillage, but Blackmer says there is evidence that soil type may impact yield when deep tilling. Some of the growers participating in the study will experiment with site-specific deep tillage next year, targeting heavy, low-lying soils.

The association's goal, Blackmer says, is to help growers evaluate their tillage system and choose for themselves.

“If you're considering adopting a new tillage practice, go out with a shovel and as you're digging, ask yourself why tillage might benefit your soil,” he says.

Blackmer adds that growers should begin by testing the alternative. “Put in a few strips of the new system, rather than adopting it on the whole farm,” he says. “Test the alternative, don't implement the alternative first.”

For more information about the ISA On-Farm Network tillage study, visit

Craig Heineman and his brother Paul farm near Ogden, IA. They'd heard about deep tillage and wanted to evaluate it, so they sought ISA's help to make sure they were following proper protocols. Global positioning systems (GPS) have helped. “GPS gives us the capability to evaluate our agronomic practices,” says Craig. “The technology has made testing available to the farmer.”

Heineman tested deep tillage in strips in three fields in 2003. The practice paid in one field, didn't pay in another and there was no difference in the third. However, he maintains that the hard-pan layer in the soil was deeper than the ripper reached the first year.

In 2004 he tried the practice in three more fields, tilling the strips about 20-in. deep. He says that depth penetrated the hard-pan layer. Assuming a 5 bu. yield increase to break even, ripping didn't pay last season either.

In one field with mostly Clarion, Nicollet and Canisteo soils, ripping had a 1.2 bu. disadvantage. In another similar field, ripping showed a 0.7 bu. yield advantage. Ripping performed best in a field with a mix of Clarion, Nicollet, Storden, Webster, Coland and Canisteo soils, where on the average it was 3.5 bu. better. Some individual soil types within the field showed yields well above the 5-bu. break-even level, but not well enough to make ripping pay for the entire field.

“We're always looking for something that might help us get better yields that will pay,” says Heineman. “We try to be as efficient as we can, and evaluating agronomic practices is part of attaining that goal.”

Tony Vyn, Extension agronomist at Purdue University, says there are four factors that impact tillage choices.

  1. Crop rotation. Vyn says the first consideration should be the intended crop and the rotation crop. In a 30-year study comparing corn-on-corn to a corn-and-soybean rotation, yield advantages ranged from 5% to 18%, depending on the tillage system. (See chart at right.)

  2. Soil type. The agronomist says there is a greater response to tillage on high-clay soils and poorly drained soils even if the field is tiled. Growers need to consider if planting would be delayed if those soils weren't tilled.

  3. Planting timeliness. “Growers need to consider if they'll need to till in order to complete their corn planting by the end of the optimum planting period,” says Vyn. Considerations include planter size, labor resources and drainage.

  4. Pest control. “Some plant pathologists tell growers that tillage will reduce the threat of foliar diseases, but I believe carefully choosing varieties is a better defense,” he says. “And there's increasing evidence that the best way to control the risk of soybean cyst nematode is to leave the field in permanent no-till.”

Vyn says the only other reason to consider tillage is to remove soil compaction. “But you have to be really sure you actually have a compaction problem that is capable of being relieved by tillage through the following growing season, not just for a month or two,” he says.

The agronomist adds that no-till systems are very short lived in the Corn Belt and that most growers practice “rotational tillage” involving no-till soybeans followed by a wide range of tillage systems from strip-till to moldboard plowing for corn. He says the reasons aren't always clear.

“The perception is that soil will dry faster after heavy rains in tilled soil vs. no-till, but that's not true,” says Vyn. “No-till soils often dry faster because they've maintained larger pores so surface water is absorbed into the soil faster.”

He advises growers to leave replicated field-length strips and encourages growers to try comparisons with untilled strips, and two different tillage systems. “The results might surprise you,” says Vyn.

Keith Schwandt farms with his father and brother near Williams, IA. They've been strip-tilling for two years and this fall they've been working to incorporate the practice on all their acres.

Schwandt likes strip-till because he can reduce his fertilizer rates 50% by banding the application. “We're using less fertilizer, but we're getting more bang for it by putting it where we need it,” he says.

However, there are several other reasons he's chosen strip-till. He's compared notes and has seen the results of other top producers. He has invested in a BeeLine real-time kinematic (RTK) auto-steer system to allow him to till and plant in the strips accurately.

“We have quite a few hogs and no overabundance of labor so it makes sense to till 15-in. strips instead of the whole field,” says Schwandt. “I know our soils will be healthier and earthworm disruption will be reduced. The no-tillers have healthier soil, but it's also colder, and those who use conventional tillage have nice warm soil. It seems that strip-till provides a happy medium.”

Another reason to introduce strip-till is to reduce compaction and Schwandt likes that idea. He uses a Zone Commander to deep-till the strips in the fall and will do so for a couple years to break up any compaction.

His comparisons have been more field-to-field, but Schwandt estimates that strip-till gives him a 2-5 bu. yield advantage in corn by reducing compaction, in addition to approximately $13.85/acre cost savings in reduced machinery wear and tear, fuel and labor, based on Iowa State University custom rates.

“We considered getting a larger combine last year so we could finish harvest faster and get more tillage done, but we looked at the expense and decided against it,” says Schwandt. “This year our fields aren't black, but because we're reducing our tillage we're also reducing the number of passes through the field significantly. With strip-till you have to be willing to farm ugly, but now we don't need a monstrous combine to get done sooner and our soils are becoming more productive. All the pieces of this system are starting to fall into place for us.”

The 2004 National Crop Residue Management Survey, conducted by the Conservation Technology Information Center (CTIC), says 41% of all cropland in the U.S. is under a conservation tillage system. No-till is the most common practice, covering 62.4 million acres in 2004, which is nearly 23% of all cropland in the country — a 13% increase from 2002. (See “Big Bump In No-Till Acres,” Dec. 2004, p. 4)

Dan Towery, the Natural Resources Conservation Service specialist who organizes the data collection, says strip-till, vertical tillage and fluffing harrows may fall under the no-till umbrella.

Research has shown that by using a continuous no-till system and controlled traffic using RTK, runoff has almost been eliminated from those fields. “That's a huge change,” he says. “This may not happen on every soil and it takes about five years, but there are clearly long-term advantages.”

He notes that while no-till has increased over the years, mulch-till has decreased. The Plains states have seen the highest growth rate lately. “Four to five years of drought or below-normal precipitation has encouraged growers to change to a diversified cropping rotation combined with no-till,” he says. The moisture savings increase yields and profits. The chart above indicates the rate of conservation tillage adoption from 1990 to 2004.

For more information about the crop residue management survey, contact CTIC, 765-494-9555 or visit

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