We have conducted field experiments, pot experiments in the greenhouse and incubations to study the nitrogen effect of different waste-based fertiliser products

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.

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Figure 1. Selection of the waste materials used in experiments. Photo: Annbjørg Øverli Kristoffersen

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.

Contacts
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Figure 2. Partitioning nitrogen in organic waste into three fractions