Corn-Soybean Rotation Update
Crop rotation describes the pattern of growing two or more crop species in a given field in some consecutive order. Soybean is commonly rotated with corn, wheat, rice, or grain sorghum in the US. The perception is that rotation of soybean with a grain crop provides positive agronomic, environmental, and economic benefits. In the Corn Belt, the vast majority of soybean is rotated biennially with corn.
In the midsouthern states, there is a lack of long-term research that documents how a biennial rotation of soybean and corn or grain sorghum will perform. However, in the 2012- 2016 period, there was an average of 2.661 million acres of corn harvested in Arkansas, Louisiana, Mississippi, and Tennessee. During the same period, harvested grain sorghum acreage in Arkansas, Louisiana, and Mississippi ranged from 101,000 in 2016 to 629,000 in 2015. All of these grain acres likely were or could have been rotated with soybean. In the 2012-2016 period, harvested rice acres averaged 1.910 million acres across Arkansas, Louisiana, and Mississippi (USDA-NASS), and it is common practice that most of this acreage would have been rotated with soybean.
Results from rotational research in the US is covered extensively here. Links to articles that cover most aspects of rotational cropping are covered and links to pertinent literature are given. Since that posted White Paper was updated in 2016, several articles with results from long-term research have been published. Major findings from that research are shown below.
A report (Al-Kaisi et al., Agron. J., Vol. 107, p. 1411, 2015) from a long-term (2003-2013) study conducted at seven locations in Iowa provided the following results.
• Three crop rotations (corn-corn, C-C; corn-soybean, C-S; and corn-corn-soybean, C-C-S) were evaluated.
• Yield and economic returns from the three rotations in descending order were C-C > C-C-S > C-C.
• The yield penalty associated with C-C was location specific, but still ranged from 11 to 28%.
• The C-C system led to a significant decline in corn yield and economic return regardless of tillage system of no-till, strip-till, chisel plow, deep rip, and moldboard plow.
• Across all locations, average economic returns/acre were $388 for C-S, $333 for C-C-S, and $227 for C-C.
• The results confirm the usual trend of corn yield decline in a C-C vs. a C-S rotation.
A report (Seifert et al., Agron. J., Vol. 109, p. 541, 2017) from an analysis of 748,374 yield records in the 2007-2012 period across the US Midwest provided the following results.
• The continuous corn yield penalty (CCYP) averaged 4.3%, and was more severe in low moisture and low yield environments.
• The continuous soybean yield penalty (CSYP) averaged 10.3%, and was more severe in low-yielding years.
• The CCYP got larger with up to 3 years of continuous corn, then leveled off; the CSYP increased with the number of years of continuous soybean.
• These results indicate that the CCYP and CSYP can be reproduced outside of controlled experiments.
A report (Ashworth et al., Agron. J., Vol. 109, p. 2017, 2017) of results from experiments conducted at two locations in Tennessee provided the following results.
• Including corn once in a 4-year rotation resulted in 8% greater yield than from continuous soybean.
• Cotton included in a 4-year rotation had no effect on soybean yield.
• Poultry litter included in the rotations increased soybean yield by 11% across locations and years compared to a wheat cover crop.
Results presented in the three above-cited reports confirm that soybean grown in rotation with a grain crop is a better agronomic practice than soybean grown as a monocrop. However, it is unreasonable to automatically assume that results from Midwest research will directly transfer to the Midsouth because of the following reasons.
• Midsouth soil properties present a much different environment for off-season maintenance of soil N levels because of higher soil temperatures and frequent long-term soil saturation that results in anaerobic conditions. This results in greater loss of soil N in the Midsouth 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 yields in the Midsouth will presumably result in different N use patterns by corn, and subsequently, less crop residue.
• The above factors will affect residual soil N levels.
• The presence or absence of irrigation will be a key factor in soybean rotation systems in the midsouthern USA.
With the above being stated along with supporting reasons, one could argue that the evidence such as that in the three above-cited examples is not applicable for promoting a rotational cropping system in the Midsouth. However, overwhelming evidence from the Midwestern US indicates that soybean production in the Midsouth could benefit from rotation with a grain crop, especially corn. And with over 2.5 million acres of corn being grown in the region, there is certainly ample acreage from which producers can gain this potential benefit.
Composed by Larry G. Heatherly, Mar. 2017, larryheatherly@bellsouth.net