The easiest way to utilise leather waste shavings is normally to produce new fuels from the most contaminated fractions for combustion or gasification. But since these waste contain up to 10% of nitrogen (N), burning it only for the energy recovery would not be rational. On the other hand, the chromium (Cr) content exceeding 5% in half of the waste stream (w/w) is too significant to be applied in agriculture. In this work, 4 acid hydrolysates from leather waste shavings both wet-white free of Cr and wet-blue with Cr were used: 2 with a mixture of acids and supplemented with Cu, Mn, Zn and other 2 as semi-product from collagen extraction using hydrochloric acid. The acid hydrolysates were prepared using a specific combination of acids under controlled conditions, ensuring the maximum release of nitrogen while maintaining the safety and integrity of the process. Additionally wet-green leather waste shavings eg. impregnated with olive extract were used followed by their 2 treatments: amendment with a biochar from “wet white” leather waste shavings and amendment with this biochar incubated with a commercial phosphorus stimulating microbial consortia BactoFos. They were applied as organic nitrogen-based fertilisers in a glasshouse experiment, consisting of 4-5 subsequent harvests every 30 days, under spring-autumn conditions in northern Poland. Ryegrass dry matter and nitrogen plant content were measured across 7 increasing fertiliser doses. Nitrogen utilisation, relative agronomic effectiveness, nitrogen use efficiency, total ryegrass dry matter and nitrogen utilisation breakdown across harvests were calculated. Biochar amended wet-greens provided the highest nitrogen use efficiencies exceeding 100% after 4 months growth (for 20 kg N/ha) and varying from 17% to 37% in particular months. This is backed up by another parameter (relative agronomic effectiveness) that for these materials exceeded 150% for single month and in total around 33%. Biochar amendments significantly increased agronomic parameters for wet-greens and their microbial treatment enhanced them even further. In sustainability aspects, assuming only the industrial partner waste potential, that gives 919,8 t of recycled nitrogen per year, which comes back to the environment in plant biomass. Recycling this type of waste can replace inorganic fertilizers reducing greenhouse gas emissions and carbon footprint.