Optimize the rotation from alfalfa to corn

 by Jeff Coulter, Extension corn agronomist

Including alfalfa in a crop rotation can provide several benefits to the first two crops of corn that follow it. When compared to rotations with only annual crops, these benefits often include reduced soil compaction, improved soil aggregation and soil infiltration rate, a reduction in soil- and residue-borne pathogens and insect pests, lower populations of annual weeds, potential for earlier corn planting, and most notably greater corn yield and reduced nitrogen (N) application requirement for corn.

Grain yield benefits

Across 15 years in Wisconsin and 21 and 30 years in Iowa, grain yield of first-year corn following alfalfa was 9 to 18% greater than that of continuous corn and 0 to 8% greater than that of corn following soybean (Mallarino and Ortiz-Torrez, 2006; Stanger and Lauer, 2008). Additionally, grain yield of second-year corn following alfalfa was 6 to 8% greater than that of continuous corn, but up to 8% less than that of corn following soybean.

Reduced nitrogen requirements 

Another advantage to including alfalfa in a crop rotation is that it reduces the N application requirement for the two crops that follow it. On medium (loamy) and fine (clayey) textured soils where alfalfa stands are two years or older at the time of termination, N application often does not increase grain yield of first-year corn following alfalfa, and it increases grain yield of second-year corn following alfalfa about one-half of the time. Nitrogen guidelines for first- and second-year corn following alfalfa based on soil texture, alfalfa stand age at termination, and alfalfa termination time are available at https://z.umn.edu/fertilizingcorn. 

To gain confidence in these guidelines, especially when low N application rates are suggested, consider applying high N rate reference strips in fields where the guideline N rates are adopted. If there is difference in corn between the high N rate reference strips and the adjacent areas, as indicated by crop size, vegetation index, leaf color, tissue N test level, or other factors, sidedressed N may be needed. If N is sidedressed, consider leaving strips where no N is sidedressed and compare yields to determine if the sidedressed N paid for itself.

Terminating alfalfa

Successful termination of alfalfa is needed to fully realize the yield and N benefits in the following corn crop, as alfalfa can compete with corn for soil water and N. Herbicide is typically needed for effective termination of alfalfa, unless there is tillage that cuts all alfalfa roots. 

When terminating alfalfa with herbicide, it is important to get effective herbicide translocation to roots. Therefore, alfalfa regrowth should be at least 4 to 6 inches prior to herbicide application and tillage should be delayed until at least 3 to 4 days after herbicide application. Although this could cause a delay in corn planting, corn yield is generally not reduced until planting is delayed beyond early May. More details on strategies for successful alfalfa termination are available at How and When to Terminate.

Conserving soil moisture

Alfalfa has high water use compared to other crops, so soils can be drier when following alfalfa. This can be a concern in areas where precipitation has been limiting or on soils with low water holding capacity. An option for conserving soil moisture is to no-till plant first-year corn into alfalfa stubble. Previous research in Minnesota and Wisconsin has shown that no-tilled first-year corn following alfalfa can produce high yields and typically does not require N fertilization beyond the N in a starter fertilizer. Alternatively, if tillage is used, soil moisture can be conserved by:

• Preparing seedbeds close to planting
• Avoid unnecessary tillage passes in the spring
• Avoid tilling deeper than needed in the spring
• Consider rolling baskets to seal in soil moisture

More information is available at Managing the Rotation from Alfalfa to Corn and Extension's Corn Production website.

References:

Mallarino, A.P., and E. Ortiz-Torres. 2006. A long-term look at crop rotation effects on corn yield and response to nitrogen fertilization. In: B.A. Pringnitz, editor, Proceedings of the Integrated Crop Management Conference, Vol. 5, Ames, IA. 29–30 Nov. 2006. Iowa State Univ. Ext., Ames. p. 198–206.

Stanger, T.F., and J.G. Lauer. 2008. Corn grain yield response to crop rotation and nitrogen over 35 years. Agronomy Journal. 100:643–650.