Growing Continuous Soybeans

In southern Illinois continuous soybean rotation has been in practice for some time. Due to the nature of our soil, soybeans have always been a better fit than corn. I have managed these acres for growers and have learned that if you can manage them carefully, beans-on-beans can be just as profitable as rotational beans. The three practices that are key to managing this rotation are weed control, soil fertility and seed selection.

Weed control
One of the biggest challenges we face in soybean production today is weed control. Over time Roundup^® (glyphosate) has lost its effectiveness on one of our key driver weeds, common waterhemp (Amaranthus rudis). This is unfortunate because Roundup’s effectiveness and overall cost per acre was unmatched. When deciding on a chemical program for a bean-on-bean rotation, it is important to build the program around residuals. My goal is to have at least five different modes of action applied throughout the growing season.

Below is an example of a solid bean-on-bean program:

• No-till
• Roundup PowerMax^® @ 32 oz per acre
• 2,4-D LV6 @ 1 pt per acre
• Zidua^® Pro @ 6 oz per acre

Followed by:

• Liberty^® @ 32 oz per acre
• Outlook^® @ 12 oz per acre
• AMS @ 2 qt per acre

This chemical program contains six modes of action and would be very aggressive against waterhemp, as well as large-seeded broadleafs. Herbicide timing is also crucial when controlling weeds. It is best to overlap chemistry between 18 – 21 days after the first application.

Fertility
Soil fertility in a continuous soybean rotation has always been questionable. Most of the growers in my geography are fertilizing every other year in a corn-soybean rotation. This has worked, but in a continuous soybean rotation it is important to set a proper foundation to avoid the yield penalty often associated with bean-on-bean.

The University of Illinois at Urbana-Champaign (UIUC) has conducted a study on continuous soybeans for 11 years. They found that over those years, continuous soybeans yielded as much as 90 percent of what rotational soybeans produced. When managing my own acres, I have found this to be solvable when applying potassium and phosphorus fertilizers in front of the beans.

Soybeans require more fertility on a per bushel basis than corn. Soil test fields to determine the fertility levels of the field and apply fertilizer based on the results plus maintenance requirements. Apply limestone as required by the soil test to maintain a pH of 6.5 – 6.8. When we provide the nutrients the soybeans need, in the right proportions, the yield penalty can be non-existent.

Variety selection
The last management practice for a successful bean-on-bean rotation is seed selection and protection. When planting back into the same crop residue, you are planting into a higher risk environment. This is especially crucial in soybeans.

When choosing a soybean variety, be sure to change it up, and not plant the same variety in the same field. Pick one that has a high disease score against sudden death and phytophthora. Soybean cyst nematode (SCN) pressure varies throughout the state so check your fields for SCN egg count so you know the risk. It is also important to plant a variety that has a good resistance to SCN. Picking the right seed treatment such as ILeVO^® or Clariva^® is also an important decision. Planting a resistant variety along with a strong treatment such as ILeVO can help mitigate the higher risk of SDS and SCN.

Growing continuous soybeans may have its own set of challenges but, when managed with the right approach, they can be by far the most profitable acres on the farm in 2018.

Prins is a Sales Agronomist with The Equity at their Greenville location. He grew up on his family’s corn and soybean farm in Northwest Illinois. Aaron has been a Certified Crop Advisor since graduating college in 2015. He and his wife, Samantha, have twin sons, Eldon and Victor. Aaron is very involved in his local Farm Bureau as well as his Church.