Biological-biochemical methods for determining maturity of composts

In order to determine maturity of about 100 composts both from Bavarian com post plants and composting experiments six biological-biochemical methods w ere developed, modified or used according to existing instructions. The tes ted parameters were content of soluble organic N of composts after drying a t 105 degrees C (N-org105), dimethylsulfoxide (DMSO) reduction, dimethylsul fide (DMS) production, respectively, redoxpotential and pH value after five hours of anaerobic incubation (Eh(5h) and pH(5h)), maximum respiration int ensity (AI(max)) and self heating capacity (T-max). Only pH(5h), AI(max) an d T-max were found nearly universally valid parameters to characterize comp ost maturity. N-org105 DMS-production and Eh(5h), however, were influenced too much by parent material, short-termed changes during composting or fact ors not reflecting the process of maturing. With pH(5h), AI(max) and T-max composts can be classified in three states of maturity (fresh, middle, matu re). To reach the state "mature" composts from large, infrequently turned p iles need some weeks of composting more than composts from small, frequentl y turned piles.