Determinazione della stabilità, della mineralizzazione potenziale dell’azoto e del valore agronomico di substrati a base di compost.

Seven composts were mixed with at 25 and 50% (v:v) of peat and used as growing media for lettuce production. The main physical-chemical characteristics and the stability of the unblended compost and the resulting 14 blend were determined by means of a respirometric test in a liquid environment. The potential N-mineralization capacity was measured during the respirometric test by the NH4+-N determination. The lettuce pot-growing test was performed with and without fertilization; plant biomass and TKN tissue content were measured after 2-month cultivation. Multiple regression analysis proved the respirometric index (defined by Oxygen Uptake Rate; OUR, mmol O2 kg-1 VS h-1) to be a good predictor for plant growth inhibition. Moreover, N-mineralization capacity showed good fitting with plant N-uptake and indicated limiting, suitable or potentially toxic conditions for plants. The coupled C and N-mineralization test gives reliable information about the potential constraints and chemical dressing requirement in compost-based growing media.