By Jonathon Howard
There is increasing interest in ‘regenerative’ agriculture. It is a system of farming that promotes a reduction in external inputs, such as chemicals and synthetic fertilisers, and focuses on ‘regenerating’ the natural assets on the farm. In doing so there is evidence to suggest the approach reduces peaks and troughs in farm revenue.
Regenerative enterprises often practice ‘polyculture’. That is, they incorporate livestock into the farming system to provide nutrient cycling on-farm. However, like all farms, the produce they create ultimately gets consumed by humans, and is turned to human waste off farm. Thus, there is a transfer of nutrients oﬀ regenerative farms to urban areas.
Some nutrients a farmer can maintain. For example, nitrogen (N) fertility can be maintained by including leguminous plants in rotations. However, phosphorus (P) is problematic. Estimates suggest that the equivalent of 85% of the phosphorus in fertilisers is removed each year in harvested grains. At some point, this nutrient needs to be replaced.
Traditional farmers just keep applying fertiliser. But in regenerative practices the focus is on enhanced soil biological function and cycling of nutrients. They try to work as far as practical as a closed system. As such manures and/or composts tend to be the key means by which to replenish soil phosphorus.
Obtaining suﬃcient phosphorus from manure or compost is difficult in Australia. Unlike other places in the world, animals are not housed over winter. Large volumes of manure can only be obtained from intensive animal production facilities such as poultry/swine sheds or red meat feedlots.
One option might be to use the solid and liquid waste streams from slaughterhouses (abattoirs). However, as Australia is relatively disease free, the bones from slaughterhouses is predominantly sold as animal feed.
Why not use human waste? Such recycling is consistent with regenerative farming practices, but such waste also contains residues of pharmaceuticals, personal care products, and pathogens. Some of this waste also comes from manufacturing and heavy industries which means it can have signiﬁcant levels of heavy metals.
This leaves us with a dilemma: the phosphorus in sewage and green waste we produce could sustain almost 5 million ha of Australian cropland, but instead we tend to treat it and simply dump it out to sea. We need to figure out a way to close the system and seize the opportunity to embrace and expand the use of recycled fertilisers in Australia.