Nitrogen release characteristics from biosolids-derived organomineral fertilizers

This study investigated the availability of nitrogen (N) following soil application of a novel biosolids-derived organomineral fertilizer (OMF15—15:4:4) in comparison with urea (46% N). OMF15 is produced by coating biosolids granules (particle size range: 1.10–5.50 mm in diameter) with urea and potash [60% potassium oxide (K2O)], which increase the concentration of mineral N and potassium (K), respectively, resulting in a balanced fertilizer material suitable for application in cereal and grass crops. The study comprised two soil types of contrasting characteristics which were incubated over a period of 90 days at 25 °C and maintained near field capacity. Nitrogen was applied at rates equivalent to 0 (control), 150, and 300 kg ha−1, and soil mineral N measured routinely using standard laboratory techniques. Results showed that the majority of N was released from OMF15 within 30 days from application (range: 40% to 72% of total OMF15-N applied) with a further 10% to 28% in the following 60–90 days. OMF15 required an accumulated thermal time of 2250 degrees-day to release between 68% and 79% of the total OMF15-N applied. From this, it was inferred that mineralization of the organic-N fraction in OMF15 is likely to progress beyond harvest of winter cereal crops in-field conditions in England. The results of this study aided the development of fertilization strategies for the best use of OMF in winter cereal and grass crops.