Changes in Colour and Germination Index as Indicators for Compost Maturity

Changes in colour and germination index as indicators of the compost maturity were monitored during the composting of Conocorpus erectus residues. The residues (leaves and small stems) were collected, cut into small pieces, moistend (65%) and mixed and placed in 2 bioreactors. The total volume of the bioreactor was 0.03 m(3). Airflow was supplied at a rate of 10 L/min. The results showed that the temperature increased and reached its maximum (54 degrees C) after 36 hrs and then decreased to 26 degrees C. The C/N ratio decreased from 25.22 to 18.48. A gradual darkening took place and the final compost was black in colour. The colour variables (L*, a*, b*) decreased with time and consequently, the Delta E*ab increased with time as indication of the colour change. The germination (G%) of radish seeds was 75.84, 65.50, 86.18, 99.96, 103.41 and 103.41%, the root length (RL%) was 83.33, 79.17, 116.67, 175, 191.67 and 202.08%, and consequently, the germination index (GI%) was 63.34, 52.14, 100.83, 175.37, 198.2 and 208.97% after 0, 3, 6, 9, 12 and 15 days, respectively. It can be concluded that the changes in colour and germination index could be used as indicators for the progress of composting and compost maturity.