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Sidedress application of nitrogen fertilizers for corn has been a common practice in Minnesota for many years.  This practice provides flexibility in nitrogen management and there are several advantages.  In recent years, there have been several questions associated with this practice.  Two frequently asked questions are:  1) how late can I sidedress nitrogen? and 2) are there advantages to combining a sidedress application with another application of nitrogen?

Results of a study conducted at the University of Nebraska provide a good answer to these questions.  The researchers who conducted the study established different levels of N deficiency early in the growing season by applying various rates of fertilizer N immediately after planting.  Additional N was then applied at different times during the growing season.  The total amount of fertilizer N did not change.  Each treatment received a total of 230 lb. N per acre.  Ammonium nitrate (33-0-0) was used as the source of fertilizer N. 

Corn yields as affected by the timing of the application of fertilizer N are summarized in the following table.

In this study, the V4 stage was measured at 13 days after emergence and the V8 stage was reached at 30 days after emergence.  There were good growing conditions early in the growing season.

In general, highest yields were achieved with a combination of some N at planting with the remainder applied at the V4 growth stage. A delay in timing of the second application to the V8 growth stage did not improve yield.  It's also important to note that high yields were also achieved with a single application of N at the time of planting.

Results of this study are appropriate for corn production in Minnesota.  As the time of sidedress N application was delayed, yield tended to decrease.  Therefore, early sidedress applications should be encouraged.  Early application has been a suggested management practice for several years in Minnesota.  This study confirms the importance of this suggestion.

The importance of the use of some fertilizer N at planting was also demonstrated in the Nebraska study.  Although the lowest rate of applied N at planting in the Nebraska study was 50 lb. N per acre, similar results would probably be measured with a lower rate applied at planting.  Nitrogen uptake is low early in the growing season.

Therefore, corn producers who plan to use a sidedress application of N should also plan on using some N at planting.  This N at planting can be in a static band or with a preemergence herbicide in a weed and feed program.

Corn producers are always searching for management practices that will improve corn production.  Early application of sidedress nitrogen is one of these practices.

Source:  Binder, Sander and Walters, University of Nebraska.