Effect of organic compost manufactured with vegetable waste on nutrient supply and phytotoxicity

Abstract

The amount of vegetable waste (VW) has increased, and demand for good quality of organic soil amendment is high. For these reasons, successive composting technique was tried to examine the possibility of increasing nitrogen contents in the compost. Collected VW was initially composted after mixing with either sawdust (SD) or cocopeat (CP) at different ratios (30–50% of SD or CP). After finishing the first composting cycle, finished compost was mixed with fresh VW at various ratios (10–30% of VW) for the second cycle of composting. Temperature, pH, electrical conductivity (EC), organic matter (OM) content, and carbon/nitrogen ratio (C/N ratio) were monitored, and compost maturity, phytotoxicity, nutrient contents and heavy metal concentration of the final compost in the second cycle of composting were measured. Temperature profiles of the first and second composts showed typical composting processes, and temperature was increased up to the range of 55–68 °C in both the first and second compost during the thermophilic period. Other chemical properties such as pH (6.60–9.10), EC (1.36–2.86 dS m−1), and OM content (49.40–64.04%) were within the ranges of typical composts. The nitrogen content (1.76–2.28%) was increased when successive composting technique was adapted. After finishing the second composting, average nitrogen content was increased at the range of 9.4–32.4% compared to the first cycle of compost. The maturity test showed that all the composts satisfied criteria of maturity level and concentration of hazardous heavy metal was below the threshold value in Korea. In conclusion, VW could be recycled to make organic soil amendment and successive composting process is an efficient technique to increase the nitrogen contents in the compost.