The agriculturally troubled fall of 2009 may be over, but here comes the sequel: a potentially wet spring. Due to the late corn harvest, many fields have yet to be tilled, and they have large amounts of residue remaining on the surface.
Normally corn residue is thought of positively because it lowers the risk of erosion and returns carbon and nutrients to the soil, but it’s not very friendly getting it through tillage and planting equipment in the spring.
Current University of Minnesota Extension recommendations are based on field trials conducted under these same types of conditions, so what we are finding can help answer your questions. Here are a couple of questions that might arise:
Should I apply nitrogen to help break down corn residue? It sounds good in theory, but no field research in the region shows increased breakdown of residues from additional N. The breakdown of residues slows during the winter. The activity of organisms is dictated by soil temperature, so additional N in the spring will not affect the rate of decomposition early in the season if cool and wet conditions persist.
Baling residue would have been a better strategy for fall than spring, but chopping residue could help break it into smaller parts to go through tillage equipment. While it is not ideal, burning residue may alleviate problems for spring. No matter what is done, make sure that the planter is equipped with row cleaners that are in good working order, especially in continuous corn where you’ll want clear rows for stand establishment.
What should I do for my fertilizer application in a wet spring? Wet soils can cause significant problems with fertilizer application. Nitrogen fertilizer sources are susceptible to gaseous losses. Poor application depth of anhydrous ammonia and surface application of urea with no- or shallow incorporation can lead to losses of ammonia gas.
Apply anhydrous ammonia to a depth of at least 4 in. Incorporate urea as soon as possible after application – if no rainfall is expected – at a depth of at least 2 in. If fertilizer cannot be incorporated, products like Agrotain can be used to lengthen the time between application and incorporation. For anhydrous ammonia, make sure the slits in the soil are properly sealing behind the knives and the ammonia is not being lost. Try to avoid direct application of urea ammonium nitrate solutions to crop residue to lessen the risk that it may be tied up in microbes when the residue is being decomposed.
Time in the spring is limited, but remember to take care when you are applying fertilizers for the 2010 crop. While fertilizer prices have decreased in the past year it still is a significant investment for your crops. Protecting that investment should be a top priority.
There are many educational resources on the commodity crop production section of the Extension Web site to provide more details about these questions. Here are links to three relevant publications, free to read online:
Fertilizer Urea Use in Minnesota: www.extension.umn.edu/distribution/cropsystems/DC0636.html
Understanding Nitrogen in Soils: www.extension.umn.edu/distribution/cropsystems/DC3770.html
Fall Tillage Management in Wet Soil Conditions: www.extension.umn.edu/distribution/cropsystems/M1278.html
By Dan Kaiser, soil and plant nutrient specialist with University of Minnesota Extension.