Urea is an organic substance; so it can't be regarded as an inorganic fertilizer. Inorganic fertilizers include ammonium nitrate as a rich nitrogen supply. Bacterial flora can deal with this compound to synthesize the required nitrogeneous compounds. I remember the "urea cycle" in my biochemistry lessons; in there, fumaric acid is also produced. Fumaric acid is also present in Krebs' cycle, giving malic acid from succinic acid. I mean that nitrogeneous compounds can combine with some physiologically active compounds to give the required chemicals.