Co-composting of pruning waste and horse manure was monitored by different parameters. A windrow composting pile, having the dimensions 2.5 m (height) x 30 m (length) was established. The maturation of pruning waste and horse manure compost was accompanied by a decline in NH4+-N concentration, water soluble C and an increase in NO3--N content. Organic matter (OM) content during composting fol3 lowed a first-order kinetic equation. This result was in agreement with the microbiological activity measured by the CO2 respiration during the process. The correlation at a high level of probability found between the OM loss and CO2 evolution showed that both parameters could be used to indicate the degree of OM degradation that is the maturity and stability phases of the compost studied. Humification parameters data from the organic matter fractionation did not show a clear tendency during the composting time, suggesting that these parameters are not suitable for evaluating the dynamics of the process. (c) 2008 Elsevier Ltd. All rights reserved.