DID YOUR CORN NEED ADDED NITROGEN? - By Randy Pryor

   Knowing how much nitrogen (N) to apply to corn is challenging. Especially in a year like this past year.  Ponding of water on a field can denitrify nitrogen.  Nitrogen can also be a part of agricultural runoff or leaching past the crop root zone.  This year, the wet, rainy weather made the situation more complicated. Did you apply additional N this past year as a sidedress?  Did it make a difference? It’s often difficult at the end of the year to know how a sidedress N strategy performed. Setting up an on-farm research test can help you validate and refine your N management approaches in the future.

   There was a CropWatch article last June authored by Laura Thompson, Joe Luck and Nathan Mueller that presented several ideas and protocols how to set up an on-farm sidedress study for nitrogen.  They also presented results of several N studies conducted by farmers participating in the Nebraska On-Farm Research Network which grew to 100 studies this year!

   My co-worker, Gary Lesoing, and I set up a nitrogen and sulfur study on a fertile creek bottom near Clatonia this past year, which was no-till corn planted into corn stubble with a spring grazed cereal rye cover crop.  So this was intensive agricultural use of the land, made possible through cover crops and no-till farming.  The protocol we used were small plots replicated five times farmer rate or preplant nitrogen applied vs sidedressing with urea or ammonium sulfate (AMS) fertilizer in dry forms at the V5 stage.  In this study there is a statistical difference in yield when applying 50 lbs of nitrogen in the AMS form as a sidedress after the farmers preplant a nitrogen application of 140 lbs of N knifed in before planting.  The AMS had a yield of 211 bu per acre versus the farmer preplant application alone of 185 bu per acre. The urea did not perform as well as the ammonium sulfate fertilizer so we experienced a sulfur response too.

   Nathan Mueller, Extension Educator in Dodge County, conducted a field length strip study with Climate FieldView in 2016.  This tool uses a process model that takes into account the major physical, chemical, and biological processes that affect nitrogen in agricultural fields. This study took place on Kennebec silt loam, Zook silt loam, Zook silty clay loam, and Alcester silty clay loam soils in a corn following corn field.  The whole field received 75 lb N/ac applied as 32% UAN with herbicide and 5 gal/ac 6-24-6 as starter. The Climate FieldView™ tool was used to determine an in-season N recommendation. The tool recommended 65 lb N/ac to be applied during the growing season. The sidedress application was made on June 11. Three treatments were evaluated: The treatments were sidedressing with the Climate FieldView rate (65 lb N/ac); Climate FieldView rate minus 30 lb (35 lb N/ac); and Climate FieldView rate plus 30 lb (95 lb N/ac).

   The study found there were no statistical yield differences between the treatments. The Climate FieldView rate minus 30 yielded 196 bu/ac, and both the Climate FieldView rate and Climate FieldView rate plus 30 yielded 201 bu/ac. This indicates that the lowest N rate tested would have been sufficient. For reference, the recommended nitrogen rate using the UNL N rate calculator (pre-season model) was 136 lb N/ac and the Climate FieldView total rate was 142 lb N/ac for the season. Therefore, both the UNL N rate and Climate FieldView rate were comparable in their N recommendation. 

   The weather in 2016 was much different than the weather we had this year.  We need to get better using in-season approaches for nitrogen management now and in the future.  That can be a profit center.  For more information on how to set up a whole field or on-farm research nitrogen sidedress study go to:  https://cropwatch.unl.edu/2019/added-N-on-farm-research