Technical lignins derived from kraft, organosolv, soda, and ASAM pulping as well as a fermented lignosulfonate from a sodium sulfite process have been subjected to oxidative ammoniation (ammoxidation) aimed at producing slow-release nitrogenous fertilizers. Reactions were carried out in liquid phase using a 1-liter, stirred, batch reactor. The effect of time, temperature, and oxygen pressure on the amount of fixed nitrogen and the CIN ratio was studied. High nitrogen contents were obtained with kraft and organosolv lignin followed by lignosulfonate. At 150 degrees C, 15 bar oxygen pressure and 90 min of reaction time, 13-14% nitrogen (based on lignin) could be fixed in the lignin macromolecule. Changes in molecular structure were monitored by FTIR spectroscopy. The crop yield of sorghum plants in pot experiments with ammoxidized kraft lignin as fertilizer was 82% of that obtained with ammonia fertilization.