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Crop Rotations With Soybeans In The Midsouthern US

Much of what I present here has been a part of my previous postings; however, a recent article in Agronomy Journal (see end of this article) has further piqued my interest in the subject and how it pertains to growing soybeans in the Midsouth. I am also proselytizing for in-depth rotation research with more than just yield objectives being conducted in the Midsouth.


Crop rotation has been and still is considered a sound agronomic practice. The US Corn Belt has long used a corn/soybean rotation to enhance production of the two crops. Summaries of results from numerous long-term midwestern US studies support rotation as a production practice in that region.

Three such summaries are:

  • literature review published on a Purdue University website presents summary results from 16 studies, each conducted for six years or more throughout the Corn Belt, that show an 8.5% (154 vs. 142 bu/acre) average increase in yield of corn following soybeans vs. following corn.

  • A summary of over 20 years of rotation research conducted in Northeast Iowa showed that:


Average yield of corn following soybeans exceeded yield of corn following corn by 34% (142 vs. 106 bu/acre) when 80 lb/acre of nitrogen (N) was used for corn, by 17% (151 vs. 129 bu/acre) when 160 lb/acre of N was used for corn, and by 13% (155 vs. 137 bu/acre) when 240 lb/acre N was applied to corn;


Corn following soybeans required less fertilizer N than corn following corn;


Average yield of soybeans following corn exceeded yield of soybeans following soybeans by 19% (44.7 vs. 37.5 bu/acre); and


N added to soybeans did not increase yield in either system.




  • report in Agronomy Journal from two long-term studies (20 years dryland and 10 years irrigated) conducted in Nebraska showed that:


Dryland corn following soybeans vs. following corn yielded 17% more (137 vs. 117 bu/acre) and 4.5% more (135 vs. 129 bu/acre) when 80 and 160 lb/acre of N was applied to the corn, respectively;


Irrigated corn following soybeans vs. following corn yielded 9.5% more (184 vs. 168 bu/acre) and 4.6% more (183 vs. 175 bu/acre) when 90 and 135 lb/acre of N was applied to the corn, respectively; and


The amount of N supplied by soybeans to the following corn crop in both the dryland and irrigated studies was estimated to be approximately 60 lb/acre/yr. This additional N does not become available until late in the growing season, thus making it difficult to detect with late-fall or early-spring soil testing.


It is unreasonable to assume that the above midwestern US results will directly transfer to growing soybeans in a rotational system in the Midsouth for the following reasons.

  • Midsouth soil properties present a much different environment for off-season maintenance of soil N levels (higher soil temperatures, frequent long-term soil saturation resulting in anaerobic soil conditions, etc.) that can result in greater losses of soil N during the winter months.

  • Higher temperatures in the Midsouth during the winter months will result in greater decomposition of crop residues between harvest and next season’s planting.

  • Lower dryland crop yields in the Midsouth will presumably result in different N use patterns by corn and less crop residues. The magnitude of these differences is not known.

  • The above factors will affect residual soil N levels.


There is a lack of long-term research that documents just how a soybean/corn rotation will perform outside the midwestern US. There is anecdotal evidence that corn yields will be greater following soybeans in the Midsouth, and this naturally leads to the assumption that rotation of the two crops will change the dynamics of their production.

A recent article in Agronomy Journal presents results from a 1991-2001 soybean/corn rotation study conducted on a site with a fine sandy loam soil at the Sand Mountain Research and Extension Center near Crossville, AL. The latitude of this location is the same as that of Verona and Clarksdale, MS; thus, these are southeastern US results.

Results from that study are:

  • Average yield of corn following soybeans was 19% (19.6 bu/acre) greater than average yield of corn following corn, and

  • Average yield of soybeans following corn was only 3.5% (1.3 bu/acre) more than average yield of soybeans following soybeans.


These Alabama results are similar to those from midwestern US studies. Even though this is just one rotation study, and the last year of its conduct was 2001, the similarity of these rotational yield trends to those from midwestern US studies are encouraging for Midsouthern US soybean producers.

Three things appear certain regarding the determination of possible benefits from rotating crops as a production practice for growing soybeans in the Midsouth.

  • The recent surge in commodity prices and costs for fuel, fertilizer, genetically modified seed, and other inputs make it imperative that agronomic findings from research be supplemented by economic analyses to determine the monetary ramifications of rotations.

  • The current widespread use of soybean varieties and corn hybrids with transgenic weed management traits, plus volatile changes in input and commodity prices, renders all but the most recent rotation research studies obsolete.

  • Long-term soybean/grain crop rotation studies are needed in the Midsouth to ascertain how to manage these crops in rotation, as well as determine how rotations will affect soil properties and pest and weed management in the rotated crops.



larryheatherly@bellsouth.net
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