Management Tips for Continuous Soybean Production

Feb 16, 2018

By Carrie Knott, Carl Bradley, and Raul Villanueva

There is a lot of interest this year in second year and even third or more year soybean. If you are thinking about growing continuous soybean this year there are several management decisions you should consider.

First and foremost, it is important to know what the soybean cyst nematode (SCN) populations are in your fields. Soybean cyst nematode is often referred to as a “silent yield thief” because SCN generally does not cause obvious symptoms on modern varieties, and soybean yields can be reduced by as much as 30% without visual symptoms. Therefore, before considering continuous soybean, it is essential to test fields for SCN, even if an SCN problem is not expected. Fall is the best time to test, but if necessary spring sampling can also be useful.

Many fields in the western part of the state are likely to be infested with SCN, but some fields may not be.  For fields with no detectable levels of SCN, management of this pathogen is not necessary; however, it is important to continue monitoring, as SCN populations will grow under continuous soybean.  For fields with SCN, it is important to know the actual population (number of SCN eggs per ½ pint of soil).  Fields with relatively low SCN egg populations (less than 500 eggs per ½ pint of soil) may not be affected greatly by SCN and could be potential fields for back-to-back soybean production.  However, it is important to realize that SCN populations will increase in continuous soybean, and that SCN egg levels could soon grow to over 500 eggs per ½ pint of soil.  Planting soybean varieties with resistance to SCN is one way to help manage SCN egg populations.  Most SCN-resistant soybean varieties rely on a single source of resistance, known as the “PI 88788” source of resistance, and unfortunately, there are HG types (historically known as races) in Kentucky that can reproduce fairly well on varieties that utilize this source of resistance.  These concerns raise a caution flag in regards to continuous soybean production, and heighten the importance of monitoring SCN egg populations in these fields every year.



In addition to SCN, most other soybean pathogens will increase in population under continuous soybean production.  Variety selection can help minimize potential yield reductions caused by diseases that these pathogens incite.  For Kentucky, a couple of these important diseases are frogeye leaf spot (caused by Cercospora sojina) and southern stem canker (caused by Diaporthe aspalathi).  Selecting varieties with high levels of resistance to these diseases and SCN (as described above) is essential in minimizing yield reductions under a continuous soybean production scenario.   

It will also be important to consider the expected yield loss of continuous soybean and to increase seeding rates and use seed treatments. It is well established, at local and national levels, that a 5-10% yield loss is expected for continuous soybean. In Kentucky, research conducted by Dr. John Grove at Spindletop Research Farm in Lexington from 2008 to 2016 indicates that a 5% yield loss occurs for second year soybean. Depending on the field, a 5% yield loss may be a significant penalty, which results in unprofitable soybean production.
 

Click here to see more...
Subscribe to our Newsletters

Trending Video