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Alfalfa/Corn Growers Needed for On-Farm Nitrogen Management Study

By Matt Yost, Jeff Coulter, and Michael Russelle


Alfalfa-Corn Rotation.jpg


Each year, corn is grown after alfalfa on about 250,000 acres in Minnesota. Upon termination of alfalfa, nitrogen (N) from soil organic matter and alfalfa shoots, crowns, and roots becomes available for at least two years of subsequent corn crops. Nitrogen credits from alfalfa to first-year corn have been extensively studied and confirmed with over 130 site-years of research in numerous states. Good alfalfa stands (4 or more plants/square foot) that are at least two years old generally provide all of the N needed (minus a small preplant or sidedress application of N in less than 5% of cases) for maximum first-year corn grain and silage yield on medium- and fine-textured soils.


Although a previous crop of alfalfa also provides N credits to second-year corn, the published "book value" N credits for second-year corn vary widely among Corn Belt states (Table 1). To build confidence in second-year corn N credits and improve net returns to nitrogen, farmers need improved decision aids for predicting N availability so that they can accurately apply N credits from alfalfa to second-year corn.


Table 1. Alfalfa N credits for good stands (4 or more plants/square foot) on medium and fine textured soils. 

Alfalfa N Credits.jpg


The pre-sidedress nitrate test (PSNT) is a widely used test to predict in-season corn yield response to sidedressed N. This test is often used for first-year corn after alfalfa, but may not be needed in most cases because first-year corn does not usually respond to N fertilizer above a small early-season application. Because larger N fertilizer rates are needed on second-year corn after alfalfa, the PSNT should be more useful on second-year corn than first-year corn. However, there is limited information about whether the PSNT can accurately predict N needs for second-year corn.


The basal stalk nitrate test is a postmortem test that indicates the amount of N that was available to a corn crop, but acceptance of this test by farmers is much lower than the PSNT. Concerns with the basal stalk nitrate test are that:  1) stalk nitrate concentrations are sensitive to late-season weather conditions and may not be indicative of season-long N availability; 2) stalk nitrate concentrations can differ greatly from plant to plant; and 3) test values do not indicate what rate of N fertilizer to apply in subsequent years. Total stover or cob N concentration may be complimentary or better indicators of available N throughout the entire first-year corn growing season, but research showing correlations for these tests does not currently exist.


Furthermore, it is not known how the basal stalk nitrate test, stover and cob total N, and soil residual nitrate in first-year corn will relate to the PSNT in second-year corn, and whether a combination of these tests will be able to predict second-year N credits more economically than the "book values." These independent tests probably do not respond to weather stresses in the same way, so a combination of tests may provide more robust predictions. Farmers in Minnesota need to know which test or combination of tests should be used to accurately and economically predict second-year N credits from alfalfa to corn. This would allow them to increase net returns by safely reducing N fertilizer inputs in some fields, while simultaneously reducing the potential for N losses.


Another important consideration for second-year corn after alfalfa is first-year corn stover management. Corn stover has a high carbon-to-nitrogen ratio, and the return or removal of corn stover from a field therefore may influence the N available for second-year corn after alfalfa. However, no research has directly addressed this question. Additionally, stover removal (or harvest of corn as silage rather than grain) may affect the reliability of the PSNT for predicting the N needs of second-year corn.


With funding from the Minnesota Corn Growers Association, on-farm research is being conducted in 2011 and 2012 by the University of Minnesota and USDA-Agricultural Research Service to improve prediction of alfalfa N credits to second-year corn. We are currently looking for alfalfa/corn farmers in Minnesota who are interested in participating in this on-farm research.


Cooperating farmer requirements:

1)      1.5 acres of first-year corn after alfalfa in 2011 with no manure applied at alfalfa termination and no more than 40 lb N/acre of fertilizer applied to the 2011 corn crop.

2)      Willing to plant this area to second-year corn in 2012, and to harvest this plot area as grain (rather than silage) after we collect small grain and silage yield samples in 2011 and 2012.

3)      Willing to assist with corn stover removal vs. no removal treatments with their equipment in the fall of 2011 after grain harvest.

4)      Willing to avoid N fertilizer and manure application to the plot area for the 2012 corn crop (we will apply N fertilizer rates).

5)      Other than above, growers will manage the 2011 and 2012 corn crops according to their normal practices using their equipment.


Benefits to cooperating farmers:

1)      $400 in the fall of 2011 and an additional $400 in the fall of 2012. 

2)      Have second-year N credits, the PSNT, and various predictors of N response tested on your farm.

3)      Be part of a large group of progressive farmers evaluating advanced N management strategies for corn after alfalfa on their farms. 

4)      Cooperating farmers will better understand corn N needs after alfalfa, which will allow them to be more efficient with N fertilizer use and increase net returns.


Interested farmers and agronomists should contact:

Matt Yost

Research Assistant - University of Minnesota

Cell:  651-402-1486



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