We have received a number of questions this spring pertaining to nitrogen loss. The following article, written by Fabian G. Fernandez, University of Illinois, addresses many of the concerns farmers are facing as they deal with wet soils.
I estimated percent N recovery by subtracting soil N in the control plot from that in the plot treated with 160 lb N/acre and dividing by the application rate of 160 lb N/acre. I present these data to provide some general information, but the values are not absolute and should be considered so, because many factors impact N recovery. Figure 2 shows that 26% of the total N was recovered within the top 6 inches of the soil and 28% within the top 12 inches. The figure also shows that 17% of the applied N is still in the ammonium form and that most N is still present in the top 6 inches of the soil, with very little movement of nitrate into the 6- to 12-inch increment. These values represent typical recovery values observed in other recent studies at a similar sampling time. For instance, percent recovery from fall-applied N was 22% and 23% in two very wet years and 54% in a year with a dry spring with low potential for N loss. Across all three years of that study, N recovery was 33%, and average loss of corn yield relative to the economical optimum N rate was less than 2%.--Fabián G. Fernández