WP 2: First results on nitrogen

From our studies we see that the nitrogen (N) mineralisation pattern of organic wastes is well described, if we partition the N into three fractions (Figure 2):

• the initial ammonium content,
• the easy mineralisable organic N and
• a slow organic N pool.

Given the mineralisation pattern from incubation studies, we have used a simple decomposition model to determine the size of the easy N pool for a number of wastes.

For the liquid organic wastes, which we have tested, the fertilisation potential is directly determined by the ammonium fraction.

For solid organic wastes, the easy mineralisable organic N pool must also be taken into consideration. This pool is turned into ammonium after three weeks under laboratory conditions (15 °C) and approximately 5-6 weeks under field conditions.

For grains, the fertilisation potential of a organic waste is, therefore, determined by the ammonium fraction plus the easy N pool.

In our further work, we are looking for rapid chemical extractions or spectrometric methods to replace the incubations to determine the size of the easy N pool.