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

Abstract

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.