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Managing the rotation from alfalfa to corn

Find practices for terminating alfalfa and managing the two subsequent corn crops that will benefit from alfalfa.

Benefits of alfalfa in the cropping system

Bar char with corn yield on y-axis, 3 locations in Iowa and 4 types of corn/alfalfa rotation.
Figure 1: Grain yield for N-fertilized corn grown in various rotations.

Alfalfa provides many benefits to cropping systems. Benefits occur both during alfalfa production and during the subsequent crops that follow.

Common benefits during alfalfa production include increased soil organic matter, decreased soil erosion and decreased soil nitrate leaching loss. Alfalfa also usually requires no nitrogen (N) fertilizer and few herbicide applications.

Crops that follow alfalfa usually benefit from:

  • Reduced or eliminated N requirement from fertilizer or manure.

  • Increased yield potential compared to following other crops (Figure 1).

  • Reduced weed, insect and disease pressure.

Alfalfa termination

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Map of Dakota, Nebraska, Minnesota, Iowa, and Wisconsin. Areas all across each state highlighted.
Figure 3: First-year corn following alfalfa from 2008-12, from Cropland Data Layers. Percentages indicate percent of total first-year crop that was corn

Corn often is planted as the first crop following alfalfa in the Upper Midwest. It was the first-year crop on about 50 percent of the acres in the Dakotas and on 75 to 92 percent of the acres in Iowa, Minnesota, Nebraska and Wisconsin during 2008 to 2012 (Figure 3).

Planting

Due to high water use by alfalfa relative to other crops, soil moisture following alfalfa can be limiting in areas of low precipitation or low soil water-holding capacity. This should be a consideration for deciding whether and when to plant corn.

On the other hand, if precipitation is adequate for growing corn, water use by alfalfa may allow for earlier corn planting. For fields where anticipated in-season soil moisture is limited, consider:

  • Terminating alfalfa earlier.

  • Planting corn early.

  • Planting drought-tolerant corn hybrids.

  • Planting shorter-season crops such as wheat.

  • Utilizing irrigation.

Nitrogen

Through a symbiotic relationship with soil bacteria, alfalfa can gather N from the atmosphere for its own growth and production. During its lifetime, alfalfa sheds and regenerates fine roots, which add N to the soil. The N content of alfalfa herbage and roots combined can be as high as 200 pounds of N per acre.

When alfalfa is terminated, the N in alfalfa residue along with increased soil N and other soil quality improvements that occur during alfalfa production typically supply large quantities of N to one to more years of subsequent crops.

This increased N supply often causes first-year corn to require little or no N as fertilizer or manure. The size of the reduction in N rate for first-year corn compared to continuous corn (corn following two or more years of corn) is commonly known as the “alfalfa N credit.”

Alfalfa N credits

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Phosphorus and potassium

It is important to monitor soil-test potassium (K) toward the end of an alfalfa stand because harvested alfalfa can remove about 160 to 300 pounds of K2O per acre each year.

If K is needed for first-year corn following alfalfa, applying K ahead of corn rather than ahead of last-year alfalfa will reduce luxury consumption of K by alfalfa and maximize K use efficiency for first-year corn.

We suggest that 0 to 255 pounds of K2O per acre should be applied to corn according to soil-test K concentration in the topsoil and expected corn yield. First-year corn should be fertilized with 0 to 160 pounds of P205 per acre according to soil-test phosphorus (P) concentration in the topsoil and expected corn yield. Be sure to credit N that may be applied with P fertilizers when determining N rates for corn.

Manure

Manure often is applied to first-year corn following alfalfa for several reasons, including the need to replenish nutrients removed during alfalfa production, insufficient manure storage capacity, inadequate land area for spreading manure in other crop rotations, and/or inability to distribute or sell manure.

However, if possible, avoid manure application for first-year corn following alfalfa because additional N often does not increase corn yield and can cause N loss to the environment. Many fields with a manure history may have adequate or more-than-adequate soil-test P and K at the end of alfalfa stands, but be sure to soil test.

If manure is needed to replenish soil P or K at the end of an alfalfa stand, apply only the minimum rate (based on a manure nutrient analysis) needed to meet P or K requirements. Consider applying solid manure if the P need is greater than K, but liquid manure if the K need is greater than P, because solid manure usually has higher P concentration and liquid manure usually has higher K concentration.

Also consider using P or K fertilizer instead of manure to meet needs of first-year corn so that manure nutrients can be used for corn in other rotations or for other crops that need N.

Insects, weeds and diseases

The potential for soil and residue-borne insects and pathogens that impact corn is usually lower for first-year corn following alfalfa than corn in other rotations.

Bt corn hybrids or soil-applied insecticides for protection against corn rootworm are not necessary when following alfalfa because the lifecycle of corn rootworm is disrupted by alfalfa.

Healthy alfalfa stands typically suppress many annual weeds that plague corn grown in crop rotations with only annual crops. This can lead to reduced weed pressure in first-year corn, and less need for herbicide.

Second-year corn following alfalfa

Corn often is planted as the second crop following alfalfa in the Upper Midwest. It was the second-year crop on 50 to 75 percent of the acres from 2009 to 2012 in Iowa, Minnesota, Nebraska, South Dakota and Wisconsin, and on 30 percent of the acres in North Dakota during this time (Figure 8).

Map of t
Figure 8: Second-year corn following alfalfa from 2009-12, from Cropland Data Layers. Percentages indicate percent of total second-year crop that was corn.

Corn can be an excellent second-year crop following alfalfa termination because the grain yield can be equivalent to corn following soybean or about 10 percent higher than continuous corn (Figure 1).

Planting

Planting second-year corn following alfalfa requires attention to residue management. If tillage is used and first-year corn is harvested for grain rather than silage, stalks from first-year corn generally should be shredded prior to tillage.

The choice of tillage system typically affects the yield of second-year corn following alfalfa more than that for first-year corn. Full-width tillage systems often produce greater yield than strip-till or no-till systems for second-year corn on fine- and medium-textured soils, especially when early-season growing conditions are cool and wet.

Nitrogen

Alfalfa typically provides N to second-year corn, thereby reducing its fertilizer or manure N requirement compared to continuous corn.

 

Alfalfa N credits

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Phosphorus and potassium

To manage P and K for second-year corn following alfalfa, use the guidelines for corn following corn.

Manure

If manure was applied to first-year corn, be sure to subtract second-year manure N credits to further reduce the amount of N applied for second-year corn as fertilizer or manure.

If the second-year alfalfa N credit (up to 75 pounds of N per acre) plus the second-year manure N credit from first-year corn do not meet the economically optimum N rate for second-year corn, use properly credited manure N or fertilizer N to bring the total N rate up to the Extension guideline rate.

Insects, weeds and diseases

Use the guidelines for corn following corn to manage insects, weeds or diseases in second-year corn following alfalfa.

Matt Yost, former graduate student, College of Food, Agricultural and Natural Resource Sciences; Jeff Coulter, Extension agronomist and Michael Russelle, emeritus soil scientist, USDA Agricultural Research Service

Acknowledgements

We appreciate the assistance of several University of Minnesota Extension educators, state agency personnel, private consultants, technical help, the USDA-National Agricultural Statistics Service and 59 growers in Minnesota, Iowa and Wisconsin. We also thank Drs. Roger Becker, M. Scott Wells, Daniel Kaiser and Fabián Fernández for their reviews.

Content on this webpage was funded by the Minnesota Agricultural Fertilizer Research and Education Council. The research summarized in this publication was supported by the Minnesota Agricultural Fertilizer Research and Education Council, the Minnesota Corn Research and Promotion Council, the North Central Region-Sustainable Agriculture Research and Education Program, the Minnesota Agricultural Water Resources Center, the Hueg-Harrison fellowship, the University of Minnesota and the USDA-Agricultural Research Service.

Reviewed in 2018

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