Effects of Composting Yard Waste Temperature on Seed Germination of a Major Tropical Invasive Weed, Leucaena leucocephala

Composting is an environmental-friendly option for yard waste management, and produces products for improving soil quality. However, there is a weed dispersal risk if the compost contains many active weed seeds. This study assessed the potential of composting in minimizing the seed germination of a major tropical invasive weed, Leucaena leucocephala. The germination of the species was tested after two different sets of thermal treatments, i.e., (1) different constant temperatures (20 °C, 30 °C, 40 °C, 50 °C, 60 °C, and 70 °C) for 5 days, and (2) composting temperature (simulating the temperature profile of a typical composting process) for 60 days. A three-month growth test was further conducted for the seeds treated with the composting temperature. The seeds were present either alone (N-seeds) or mixed with wood chips (W-seeds) when thermally treated. A constant temperature treatment of 70 °C suppressed the seed germination to a low rate. For the composting temperature treatment, the germination percentage of the N-seeds and W-seeds were reduced from around 60% to 22.7% and 12.7%, respectively. This preliminary study suggested that the temperature should reach as high as 70 °C in the composting process to guarantee the suppression of the germination of the seeds of L. leucocephala, particularly when the seeds are contained within seed pods during composting.