Nitrogen in biowaste and yard waste compost:: dynamics of mobilisation and availability -: a review

According to the Austrian Water Act, the maximum permitted nitrogen load from fertilisers is 175 and 210 kg N ha(-1) year(-1) for arable land and for grassland, respectively. In organic farming, the maximum life stock related N load is restricted to 170 kg ha(-1) year(-1). In the regulations of the Austrian Program for Environmentally Sound Agriculture, it is assumed that 25% of the total N in fresh manure are available to plants in the first year, a value that may be disputed. Compared to other forms of fertiliser (mineral, slurry, animal manure or sewage sludge), biowaste compost leads to an enhanced enrichment of organic (humus-) nitrogen in the soil. Depending on the cultivation system a site-specific humus content and C/N ratio will be reached. In the present paper, several studies on N-mineralisation from composts are compiled. As a rule the immediate N-effect in the first year is less than 15% (5-15%) of the N-total-supply by compost followed by 2-8% year(-1) of the remaining compost-N in the following years. Model calculations show that the balance between compost-N supply and N-uptake and losses will be obtained within periods of 40-100 years when compost is applied regularly. Improved knowledge of the C- and N-turnover from composts and in the soil organic matter pools will be the key to a specific control of the system including the potential negative impact on the ground water. (C) 2003 Editions scientifiques er medicales Elsevier SAS. All rights reserved.