Nitrogen fixation of various material from a number of European countries by three nitrogen fixation tests

Three methods for determining N fixation were evaluated using a wide range of growing media materials from 4 countries. The short term method (Nitrogen Drawdown Index method) was poorly correlated with the long term method (N-retention method) but was better correlated with the medium term method (N-immobilization), On the other hand the medium term method was more strongly correlated with the long term method. It was concluded that a short term method is unlikely to give reliable results for all materials. The N retention test carried out on two types of woodfibre produced by two thermomechanical processes fixed significant amounts of N. However, when a N source was added during the thermomechanical process, the product released significant amounts of N during incubation. This would put severe limitations on products produced from these material where the product would need to be stored.