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Grower Cooperators Needed for On-Farm Validation of Manure and N Fertilizer Requirements in Alfalfa-Corn Rotations

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By Matt Yost - Graduate Research Assistant, Michael Russelle - USDA-ARS Soil Scientist, and Jeff Coulter - Extension Corn Agronomist.

Integrating alfalfa into crop rotations can reduce the need for purchased inputs for corn such as nitrogen (N) fertilizer, improve soil structure, remove excess nitrate, improve soil organic carbon, disrupt pest and disease cycles, and it may even increase economic returns. Many Minnesota growers are aware of the current University of Minnesota guidelines for a N credit of up to 150 lb N/acre to first-year corn when the previous alfalfa stand is greater than 4 plants/ft2, yet recent reports from farm surveys suggest that many growers do not trust current estimates of alfalfa N credits. Applying excessive N fertilizer or manure to first-year corn after alfalfa can decrease profit and have environmental consequences, but under-applying N to corn can reduce yield and profit.

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On-farm research beginning in the fall of 2010 will expand current on-farm research on alfalfa N credits to corn by directly comparing grower practices (N fertilizer or manure application) to current recommendations when alfalfa is terminated with intensive tillage, and by determining the N credit in no-till or minimum-till systems. This research will also evaluate the effectiveness of the pre-sidedress nitrate test (PSNT) in first-year corn after alfalfa to determine if it can predict whether an adequate N supply is present and if additional N is needed. The results from this research should help growers improve their understanding of the N requirements for first-year corn after alfalfa.


We are currently seeking 30 conventional and organic growers with suitable fields representing two categories of tillage practices (no-/minimum-tillage and conventional tillage) to cooperate in this research. Suitable alfalfa fields will have good stands (at least 4 alfalfa plants/ft2), will be terminated in the fall of 2010, and will be planted to corn in the spring of 2011. Of these, we are looking for 10 fields that will be planted to corn using a no-/minimum-till system. In these fields, we will add different N rates to determine what the economically optimum N rate is for no-/minimum-tillage conditions.


The other 20 fields that we are looking for would use conventional tillage operations such as chisel plowing, disk-ripping, or moldboard plowing to terminate alfalfa. In ten of these conventional tillage fields, we would compare the grower's normal rate of N fertilization for corn with no fertilization. In the other ten conventional tillage fields we would compare the grower's normal rate of manure for corn with no manure. We will apply fertilizer to plots if the grower does not plan to fertilize.


Growers will receive a small honorarium for cooperating in applying N input treatments in the spring of 2011. Interested cooperators with suitable alfalfa fields should contact Matt Yost at or 651-402-1486.


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