Determination of biological stability in compost: a comparison of methodologies

The compost stability of fifteen end products was assessed by the use of biological (Dynamic Respiration Index, DRI), chemical (humification indexes, HI, DH, HR) and thermoanalytical (thermostability index, R1, and labile fraction) parameters. Assessment of compost stability carried out independently by means of each of the three techniques gave evidence of not well stabilized materials for the presence of easily biodegradable, labile, no-humified organic fractions. Significant correlations were observed for DRI vs. no humified carbon (NHC) (r = 0.789; p<0.01) and labile fraction determined by thermogravimetry (r = 0.651; P<0.05), and for NHC vs. labile fraction (r = 0.631; P< 0.05), all representing easily biodegradable, labile and no-humified fractions. Significant correlations were also observed for the three indexes above with TEC (r= 0.790, P<0.01 for DRI; r= 0.839, P< 0.01 for NHC; r= 0.888, P< 0.01 for labile fraction ), whereas no significant correlation was observed between DRI and the humification indexes HI, DH, HR and the thermogravimetry index R1. These results suggest that the integrated use of biological, chemical and thermoanalytical parameters could represent an useful tool for differentiating stabilized composts from non stabilized ones, and it could provide a more reliable information for both the management and the sanitary health aspects bound to good agricultural practices.