146 / 172
(MMU = monomethylolurea; MDU = methylenediurea; DMU = dimethylolurea; and HMT = hexamethylenetetramine)
Therefore, the direct determination of the amount of SRN by summingthe amounts of reacted organic N
from various forms is not a viable option. Consequently, SRN content is most often determined as the
difference of the unreacted free urea subtracted from total the N, both of which can be fairly easily
determined. The remainder from this subtraction is the combined reacted organic N (or SRN), except in
cases where some other nitrogen form such as nitrate may have been added after the reaction in order
to make a mixed fertilizer.