Cover crops after corn silage in Dane County

Heidi Johnson, Dane County UW-Extension Crops and Soil Agent

For the last three years, Dane County Extension and Yahara Pride Farms (a farmer-led watershed group) have conducted cover crop plots to evaluate what cover crops work best after corn silage in this region.  We have evaluated planting dates, cover crop species, planting rates and various planting methods.  Here are the take home points we have learned from the plots:

  • Species selection
    • Radishes, peas and legumes don’t work well planted this late in the season.  We only recommend grasses such as rye, barley or oats for planting after corn silage harvest.
    • Barley and oats are only good choices if they can be planted prior to Sept 20th.  When they are planted later than this, there is not sufficient cover crop residue in the spring to provide erosion control.
    • Winter rye is one of the only cover crop choices for a later silage harvest (after Sept 20) but it does continue to grow in the spring and requires careful management in the spring so it doesn’t affect the cash crop.   Winter rye should be terminated 7-14 days prior to cash crop planting.
  • Seeding rates
    • Lower planting rates of 30-50lbs are sufficient for winter rye, higher rates create more residue and can impede cash crop planting and growth
  • Planting method:
    • Post-harvest broadcast seeded cover crops lag significantly behind those planted with a drill.  Using a drill is preferable at this point in the season with limited days for growth.  Broadcast seeding may be more effective if it is done prior to harvest with an airplane, leaving more time for cover crop growth.
  • Nitrogen management
    • We conducted nitrate sampling of the soil under different cover crops to determine if a nitrogen taken up by the cover crops in the fall is returned to the cash crop.
    • We found that about 40 pounds less nitrogen esd  available in the soil in June where there had been a winter-surviving cover crop (rye or wheat).  There was similar nitrogen availability between winter-killed cover cropped (oats or barley) ground and ground that had not had a cover crop.

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