1. Proteinaceous constituents are stabilized through their reaction withother organic constituents, such as lignins, tanins, quinons.
2. Biologically resistant complexes are formed in soil by chemical reactionsinvolving NH3+ or NO2- with lignins or humic substances.
3. Adsorption of organic N compounds by clay minerals (pariculary montmorillinitic types) protects the molecule from decomposition.
4. Complexes formed between organic N compounds and polyvalent cations, such as Fe, are biologically stable.
5. Some of the organic N occurs in small pores or voids and is physicallyinaccessible to microorganisms.