Improving Continuous Soybeans

The benefits of crop rotation for soybeans have been well documented. Soybeans yield at least 10% better when rotated with corn and wheat, rather than grown continuously. On very heavy soils, when corn and cereal crops may not be reliable options, many years of soybeans result in some rotations. Not all the yield benefits from crop rotation are fully understood. However, some of the yield increases can be attributed to lower insect and disease pressure, improving soil organic matter, decreased erosion and improved soil structure.

Will A Cover Crop Improve Soybean Yields?

Soybeans make the soil 'tighter' due to a reduction in the stability of aggregates, which makes soils more prone to compaction. Could soil structure be significantly improved by planting a cover crop in the fall immediately after soybean harvest and leaving that cover crop until the spring prior to the next soybean crop?

A few producers in southwestern Ontario have experimented with growing an oat or rye cover crop after soybeans in an effort to increase soybean yields. Is there evidence that growing a cover crop may provide a yield benefit for continuous soybeans? In a US study where cover crops were broadcast into a standing soybean crop at leaf-drop, the following year’s soybeans yielded significantly higher. Refer to Table 1.

Table 1. Second Year Soybean Yield Improvements Due to Cover Crops. (Lancaster County, Pennsylvania, 1999-2001)

*Rape data from 2000 and 2001 only. Data from Penn State Research and Extention Center, Landisville.

Cover Crop Trials

The St. Clair Region Soil and Crop Improvement Association is going to experiment with seeding cover crops in continuous soybean fields, starting this fall. In order to establish a good stand the cover crop will be no-till drilled or broadcast and incorporated. Broadcasting seed into a standing soybean crop has been tried in the past with limited success. This year both winter wheat and rye (for those willing) will be evaluated as a cover crop for continuous soybeans. If you wish to get involved please contact Adam Hayes or Horst Bohner.

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