Millipedes and earthworms: a comparison of their efficiency and the quality of the resulting products.

ABSTRACT Millicomposting (MIL, with millipedes), vermicomposting (VER, with earthworms) and composting without invertebrates (CNT, control) were compared for the first time in a replicated controlled experiment to evaluate their efficiency and the quality of their products. Vegetal waste was degraded in small closed digesters to emulate household-scale composting. Temperature profiles were similar in the three composting types. Ninety-two days were enough to complete composting and obtain well-stabilized products (humus with C/N< 20; pH from 7 to 7.8). The mean final volume loss was about 8% higher in VER than MIL and CNT ( P  < 0.01) and it stabilized between the 32nd and 67th days (51.4% in VER, 43% MIL and 44% in CNT). Both invertebrates promoted gains in humus Ca content (about 34.5% higher compared to CNT), whereas the highest K and Mg contents were observed in VER humus. pH, P 2 O 5 , and S contents were also higher in VER humus than in CNT (all P  < 0.05). The leachate volumes, electrical conductivity and Na + and PO 4 3- contents were similar ( P  > 0.05), while pH and contents of K + and NH 4 + were higher and NO 3 - was lower in VER than in MIL (all P  < 0.01). This resulted in higher maturity degrees in MIL than VER (NH 4 + /NO 3 -  = 0.01 and 0.93, respectively). Although all three composting types were efficient in producing mature high-quality organic fertilizers, this study showed that the addition of invertebrates improved the composting efficiency and the quality of the final products.