Disclosed are compositions and methods of making a liquid fertilizer additive of biodegradable polymers and/or oligomers comprised of utilizing a non-aqueous polar, aprotic organo liquid (NAPAOL) as the reaction medium for the reaction of aldehyde(s) with cyano-containing nitrification inhibitors that have one or more groups that react with the aldehyde(s) wherein said reactive groups are selected from the group consisting of a) primary and secondary amines, b) amides, c) thiols, d) hydroxyls and e) phenol.