Un metodo standardizzato per la determinazione della stabilità della sostanza organica da compost.

Important characteristics for agricultural soil improvers are the supply of organic matter (OM) and plant nutrients. Practice asks for simple, quick and cheap methods to determine the stability and N-mineralization potential of composts and soils. A standardized method for the simultaneous determination of the intrinsic carbon (C) and nitrogen (N) mineralization rates of natural OM sources (soils, composts, manures, etc.) was developed by means of an aerobic incubation in a suspension of the sample in a nutrient solution. The proposed method, recently well discussed by Grigatti et al. (2007) in Soil Biology & Biochemistry, is based on determination of the oxygen (O2) consumption, monitored indirectly via pressure drop measurement, and on determination of N mineralization, through the periodical measurement of the solely NH+4-N in the liquid suspension. This method also rules out the effect of soil conditions or compost bed characteristics and thus reflects the intrinsic properties of the OM. The method is faster and more reproducible than soil incubation tests that are currently used. In such a system it is important that nitrification is inhibited to avoid O2 consumption by nitrifiers and prevent the production of gaseous Ncompounds (i.e. N2O). N-Allylthiourea completely suppress nitrates (NO3-) formation without suppressing the heterotrophic microbial activity, thus allowing the correct determination of the OUR. When nitrification inhibitor was added, N2O could not be detected anymore in the gas phase of the system, which confirms that nitrification was inhibited and indicates that denitrification and nitrifier denitrification activity was negligible. The method cannot only be applied by advanced laboratories, but also by e.g. compost producers (to monitor and optimize their composting process) and end-users (to assess compost quality). On basis of measurements of different types of composting mixtures at various composting time, the suitability of the method for compost coupled to nitrogen mineralization is showed.