AOAC RI ERP EBOOK FOR FERTILIZERS

data sheets, product labels or otherwise, is unfortunately not always as an easy task for the potential user. In this matter, particular attention must be paid to the methods used by various manufacturers for the determination and reporting of the amount of SRN, and CRN present. The SRN in most commercial liquid SRN-containing fertilizers presently manufacture in the United States, Canada, and Europe is comprised of the water-soluble reaction products of urea with formaldehyde, or from the reaction products of urea, formaldehyde and ammonia. In the reaction of urea and formaldehyde, based on the nature of the catalysts, whether an acid catalyzed reaction, or a based catalyzed reaction, different urea-formaldehyde adducts (ureaforms) will form and the resulting product will be either liquid or solid 4 .

O

O

Base

H 2 N

NH 2

H H

+

Urea

O

O

CH 2 OH

HN

NH

CH 2 OH

+

CH 2 OH

H 2 N

NH

DMU b

MMU a

O

Acid

O

+

H H

H 2 N

NH 2

O

O

O

O

O

+

HN

NH 2

NH

H 2 N

NH

H 2 N

HN

NH

HN

NH 2

CH 2

CH 2

CH 2

MDU c

DMTU d

a monomethylourea; b dimethylolurea; c methylenediurea; d dimethylenetriurea

Reaction of urea and formaldehyde is not 100% and some unreacted urea will remain in the final product. If the reaction product is a solid, the amount of unreacted and free urea could be determined by AOAC Official Method 945.01 (Water-Soluble Nitrogen), and AOAC Official Method 955.05 (Nitrogen Activity Index). Determination of water-insoluble nitrogen in mixed fertilizers has been studied by Katz, et.al. 5,6