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Agronomy Update

Management Considerations for Continuous Soybean Rotations

Published on Wednesday, February 22, 2017

Many farmers across the state are having discussions around what their crop rotation will be for the coming year. Should they keep their rotation the same? Or would it be economically advantageous to plant more soybeans? In my experience, many farmers typically debate this question but then end up staying the course and keeping their rotation intact. This year however feels a little different. Given the state of the current commodity markets and soybean production levels amongst individual operations, some farmers are seriously debating planting more soybeans in 2017. That said, if you’re looking at a continuous bean rotation, there are management practices to keep in mind along the way. 
 

VARIETY SELECTION

Variety selection is paramount to maximize yields and minimize the effects of yield robbing pests such as soybean cyst nematode (SCN), sudden death syndrome (SDS) and Phytophthora root rot.  Be sure to keep the following considerations in mind as you select your varieties for continuous soybean acres.

  • Soybean Cyst Nematode (SCN):  If possible, change your source of resistance from the variety you planted in the same field in 2016. There are only three major sources of resistance incorporated into commercial varieties today. Ohio now has some fields with sizeable SCN populations that can reproduce on soybeans developed with PI88788, the most common source of resistance in our industry today. Dr. Anne Dorrance of The Ohio State University has confirmed that to date, SCN has been found in 68 counties throughout Ohio. If you haven’t yet tested your fields for SCN populations, I recommend that you select varieties under the assumption that you do have SCN present in your fields and then sample for it this fall.

  • Sudden Death Syndrome (SDS): This disease overwinters by producing survival spores, which can survive in our fields for years. SDS is prominent in fields with poor drainage, compaction issues, or those that have earlier planted soybeans. Be sure to select a variety with a high level of tolerance and utilize Escalate SDS with ILeVO® to defend against the disease. ILeVO also has activity on SCN as well as Septoria brown spot suppression. Beck’s two-year Practical Farm Research (PFR)® study has demonstrated an ROI advantage of over $4/A. when using Escalate SDS. Similarly, our three-year, multi-location data exhibits a $11.42/A. advantage using Escalate SDS versus Escalate™ alone. These numbers are pretty impressive considering that many of our PFR sites, Ohio included, visually had almost no SDS presence this past season.

  • Sclerotinia White Mold (SWM): Avoid planting soybeans back-to-back in fields that had SWM in 2016. While conditions must be favorable for this disease to infect our soybeans, sclerotia can survive in soils for a long period of time. Thus, the risks associated with this mold are great and the potential yield loss is enormous for fields with a recent history of SWM.

  • Phytophthora Root Rot (PRR): The risk of PRR infecting second year soybeans has not necessarily increased, but variety selection and seed treatment choice is key to keeping it at bay. In order to control seedling phytophthora, your seed treatment must include a systemic fungicide of either metalaxyl or mefanoxam. Beck’s Escalate seed treatment contains a high rate of metalaxyl for maximum control of seedling phytophthora. Keep in mind, your seed treatment will only protect the seedling for approximately 17 to 35 days. After this window, we rely on field tolerance to PRR, which does not initiate until the V3 growth stage. Be sure to select a soybean variety with adequate resistance to phytophthora to ensure season-long protection.

  • When planting to second year soybeans, make sure to use a reproductive variety. Second year or continuous soybeans tend to be more vegetative due to the legume nitrogen they receive from the previous year’s crop. Remember, you don’t get paid for how your crop looks, just how it yields. Plant a variety that will devote more of its energy to reproduction instead of varieties that tend to produce more height and vegetation.

FERTILITY AND SOIL MANAGEMENT

Fertility requirements and soil management are different when planting continuous soybeans then for a rotational acre. It’s important to remember that soybeans act as their own nitrogen (N) factory. In order for the rhizobia to efficiently fixate N for the soybean plant, they need to be in a neutral soil pH.  Soybeans require approximately 5 lbs. of N/Bu. Exchangeable potassium is also critical for high-yielding soybeans as they have a much higher demand for potash than a corn crop. According to the Tri-State Fertilizer Recommendations, a 55 Bu./A. soybean crop removes 130 lb. of 0-0-60 while a 180-bushel corn crop only removes 80 lb. of potash. Potassium is also essential to continuous soybeans as it aids in disease tolerance and influences soybean seed size. Increasing the overall soybean seed size is one of the most impactful components to increasing overall soybean yields.

FOLIAR DISEASE

Managing foliar leaf diseases and diligent scouting are also critical to a successful continuous soybean crop. Since we are inserting soybeans into an environment with a naturally higher inoculum level due to the previous soybean crop, our fields are more vulnerable to foliar diseases so we must wisely manage these potential diseases in a timely manner. Leaf diseases have the ability to adapt quickly and build resistance to certain classes of foliar fungicides when used repeatedly. Frogeye leaf spot is one disease that has become more prevalent over the last few seasons, especially south of I-70 in Ohio. Frogeye has a confirmed resistance to the strobilurin class of fungicides so when managing foliar diseases, such as frogeye leaf spot, be sure to utilize fungicides with more than one mode of action. Products like Stratego® YLD, Preemptor™ SC, and Priaxor® D provide multiple modes of action. Timely scouting and applications are paramount to minimizing yield loss due to foliar leaf diseases. If disease presence doesn’t dictate an earlier or rescue application, specifically at the R3 growth stage, a fungicide and insecticide is warranted and has provided a $17/A. ROI over the last seven years at our PFR sites.

According to Michigan State University, a soybean after soybean rotation will generally result in a yield reduction of five percent due to the rotation effect compared to a soybean after corn rotation.  However, high-yielding continuous soybeans are achievable with proper variety selection, attention to fertility requirements and proper disease management.

 

 

 

 

 

 

 

 

 

Practical Farm Research (PFR)® and Escalate™ are trademarks of Beck’s Superior Hybrids. ILeVO® and Stratego® are registered trademarks of Bayer CropScience. Priaxor® is a registered trademark of BASF. Preemptor™ is a trademark of FMC Corporation. 

 

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