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Don't sweat missing fall tillage

If you're kicking yourself this spring because you ran out of time to till wet fields last fall, relax.

That's because an Iowa State University (ISU) study following a soggy 1993 growing season showed no yield benefit from fall tillage. When fuel, equipment, and time were factored in, fall tillage didn't cover costs.

It's important to note that other trials have shown cases where fall tillage increases profits, says Mark Hanna, ISU Extension agricultural engineer. But these same trials have also shown that, on average, fall tillage following a wet season can cost farmers.

"Consider the amount of extra yield required to cover fall tillage costs," says Hanna.

Each growing season differs. Still, the soggy conditions of 1993 parallel those of 2008 and 2009 in many areas. In the ISU study, researchers worked with four cooperators at five sites in southeast Iowa. These fields had received 66% to 85% above-normal rainfall during the April-to-October 1993 growing season.

The ISU study examined these treatments following the 1993 harvest:

  • Deep tillage using a ripper approximately 12 inches deep.
  • Moderate tillage with a chisel plow or disk at a 6- to 7-inch depth.
  • Shallow tillage (2 inches with a field cultivator in spring).
  • No fall tillage.

The shallow tillage treatment resulted from cooperators tilling previously untilled soil areas. That's because they were concerned about being able to plant in these untilled soil areas following a wet 1993. Both deep and moderate trials were also shallow-tilled in spring to level the soil prior to planting.

Researchers measured soil compaction and yields during 1994. Soil compaction amounts were determined by bulk density soil samples and penetrometer resistance readings. Bulk density measures total soil volume, which takes into account the soil's solid and pore space. Loose and porous soils -- conducive to good plant emergence and growth – have lower bulk densities than compacted soils.

The findings?

  • Tillage had no statistically significant impact on 1994 yields following 1993's extremely wet or ponded soil conditions. With no yield increase, deep and moderate tillage were more expensive than shallow tillage or no tillage.
  • Chisel plowing costs range between $10 and $15 per acre, with deep tillage costing between $15 to $20 per acre.
  • Fall tillage following a wet year made little difference alleviating compaction. Bulk density measurements showed no soil loosening differences between tilled and untilled soils.
  • Deep tillage did lessen penetration resistance. So did moderate tillage in the spring following fall tillage. The effect did not linger into the growing season, however.
  • Natural factors like winter freeze-thaw cycles or growing-season shrink cracks may have done as much or more than fall tillage to loosen soils, says Hanna.



If you're kicking yourself this spring because you ran out of time to till wet fields last fall, relax.

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