What was it all about?

This project explored the effectiveness of new ways of recycling organics into products that would enhance productivity, as well as improve environmental health and carbon sequestration. Urban waste and horticultural waste were both investigated.

New techniques for converting waste organics involve pyrolysis to produce biochar, and these were compared with conventional composting. Biochar is produced when organic material is subjected to high temperature (350 to 700 degrees C) in an oxygen limited or zero-oxygen environment. This process produces a solid, charcoal-like residue, biochar, which is purported to enhance soil physical, chemical and biological properties and ecosystem health, with plant growth and crop yield benefits.

This work investigated three different commercial pyrolysis technologies. Green waste was the primary feedstock, with some papermill waste, woodchips and sugarcane trash.

Long term field trials with annual vegetable versus perennial fruit crops were carried out to evaluate the use of biochar and compost on crop yield, soil health and carbon sequestration.

Main findings included…

• Overall, biochar enhanced plant establishment, long term perennial plant success, soil quality and carbon sequestration for horticulture, but results were inconsistent across the methods of production
• Compost and biochar production are complementary, since fine green waste is best for producing compost, while woody feedstocks are best for biochar production
• Some biochars produced better seed germination, better plant establishment and more robust seedlings and plantlets.

Once consistent and cost-effective biochars are available, they promise to be most useful as carbon rich matrices that can be dosed with compounds for more controlled release to plants. In soils and growing media, it can provide homes for plant-promoting microbes, physical structure, improved water holding and levels of carbon.