Agronomic potential of mineral concentrate from processed manure as fertiliser

Processing of manure intends to increase the use efficiency of nutrients. A concentrated solution of nitrogen (N) and potassium (K) (‘mineral concentrate’) is one of the possible products resulting from manure processing. A study is carried out in the Netherlands to determine the agronomic and environmental effects of the production and use of such mineral concentrates. This concentrate is produced by reverse osmosis of the liquid fraction of separated livestock slurry. On average 92% of the N in mineral concentrate is present as ammonium-N, the other 8% as organic N. Pot experiments with different soils and crops showed that the Nitrogen Fertiliser Replacement Value (NFRV) of mineral concentrate compared to calcium ammonium nitrate (CAN) ranged from 76 – 97%. The NFRV of injected mineral concentrate compared to CAN ranged in the field experiments from 72 – 84% for arable land and 54 – 80% for grassland. NFRV of injected mineral concentrate was similar to that of injected liquid ammonium nitrate. Mineral concentrate is an ammonium (NH4) containing fertiliser with a high pH (about 8). Experiments showed that application of mineral concentrates may result in ammonia (NH3) and nitrous oxide (N2O) emissions. Injection or incorporation of mineral concentrate strongly decreased NH3 emission. The N2O emission from mineral concentrate is probably related to the presence of organic carbon in concentrates and/or high NH3 concentration in the soil. The risk of nitrate leaching from applied mineral concentrates was similar or lower than that from CAN, for both grassland and arable land. Obviously, NH3 emission and denitrification were the dominant N loss pathways after application of mineral concentrate. There is scope to decrease N losses and increase NFRV of mineral concentrate by use of low NH3 emission application techniques, and a further decrease of the organic N content of concentrate. Scenario analyses on national scale showed that large scale use of mineral concentrate and the attending solid fraction in the Netherlands decreased the need for mineral N and P fertilisers up to 15% and 82%, respectively. Moreover, the manure surplus in Netherlands decreases up to 84% and therefore this manure has not to be exported. The total NH3 and N2O emissions and N leaching in the Netherlands hardly changed in the scenarios. Large scale use of mineral concentrate increases the N and P use efficiency on a national scale. Key words: fertiliser, manure, mineral concentrate, nitrogen, potassium, processing, reverse osmosis