Biomass production of fodder sorghum (Sorghum sp.) has been tested in a field trial over two harvesting periods under natural meteorological conditions using ammoxidized kraft lignin (AKL) as a slow-release fertilizer and urea as conventional reference. In the course of the first growth cycle, plants treated with urea gave higher biomass yields because of the better solubility of urea in the initial phase. However, during the second cycle AKL treated plants performed better than urea treated sorghum, indicating that nitrogen from AKL became readily available.

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 C/N ratio was studied. High nitrogen contents were obtained with kraft and organosolv lignin followed by lignosulfonate. At 150°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.