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Washington State University Extension

Irrigated Agriculture

Using Crop Residues to get out of the Dammer Diking – Tillage Cycle

By Andrew McGuire
Previous corn field disked to smooth over dammer diker holes, then planted. Note bare soil.

Previous corn field disked to smooth over dammer diker holes, then planted. Note bare soil.

Farmers wanting to maintain more crop residue cover on their fields are often prevented from doing so by previous dammer diking. While dammer diking controls runoff under center pivot systems, it also leaves large holes in the field, making it impossible to plant a following crop without tillage. The tillage required to smooth the soil surface for planting also buries most of the previous crop’s residues. The bare soil is then susceptible to surface crusting, poor infiltration, and runoff. To fix this, farmers dammer dike their fields, continuing the dammer-diking – tillage cycle. The way out of this cycle is to maintain a crop residue cover on the soil surface. 

Research shows that the amount of soil covered by residue is the most important factor influencing water infiltration into the soil. Crop residues covering the soil surface can often double water infiltration rates. The residue cover does this by protecting the soil surface from water drop impact, thus preventing surface crusting. Combined with reduced tillage, residue cover allows surface soil structure to build, leading to increased water infiltration and reduced runoff. This is what you want, but how do you get there?

To escape the dammer diking – tillage cycle, you have to plan to keep your crop residues on the soil surface, and that means reducing tillage. The easiest way to do this is after perennial forage crops like alfalfa and timothy, which are not generally dammer diked. To be effective, however, you must plan to leave some residue on the soil surface. This means not taking a last cutting or taking an early last cutting to allow some regrowth before the crop is sprayed out or goes into winter.

In other crops, the exit from the dammer diking- tillage cycle is not so easy. At some point you just have to stop dammer diking (currently not an option in crops like potatoes). This can work better in a densely planted crop like wheat where there is less bare soil than in widely spaced corn rows. Let me know if you have other ideas of how this could work?

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