Scientists dig up soil secrets of Adelaide's community gardens

For the first time, University of Adelaide scientists have surveyed the soil health of community gardens across Adelaide to assess their suitability for urban agriculture.

Urban agriculture – food production systems inside city boundaries or densely populated areas – can have significant social, economic and ecological benefits and has the added benefit of minimising transport and distribution chains.

However, this is not well researched and little information regarding the health of urban soils is available.

“Urban agriculture can contribute to sustainable food production by reducing transportation routes and food imports, which in turn contributes to a reduction in greenhouse gas emissions."Professor Tim Cavagnaro

In a study published in the Journal of Cleaner Production, researchers from the University’s Waite Research Institute investigated key aspects of soil health and good land management at 12 urban agriculture sites across the Adelaide metropolitan area.

They measured the crop biodiversity, abundance of beneficial arbuscular mycorrhizal soil fungi, and levels of soil fertility and soil contamination at each site. The chemical and biological make-up of the soil was analysed, including concentrations of plant-essential minerals and potentially toxic metals.

PhD student Matt Salomon in the University’s School of Agriculture, Food and Wine, said the results of the study showed that urban agriculture sites could be sustainably managed and provided multiple benefits to the local community. They found a diverse range of food crops grown (over 70 plant species), metal concentrations below national guideline levels for all sites, and healthy levels of mycorrhizal fungi present in all sites (a good indicator and improver of soil health).

“Although we found that sites with previous industrial history showed elevated levels of potentially toxic metals when compared to sites without an industrial history, this could be overcome by using raised beds with introduced soils,” says Matt Salomon.

Project leader and Professor of Soil Ecology, Tim Cavagnaro, said that while there is great potential for urban agriculture to produce food, there are opportunities to help increase the productivity, sustainability and soil health of these systems.

Soils commonly had high phosphorus because of the use of horse manure from horse racetracks. Horse manure is very rich in phosphorus.

“Our study demonstrates that a developed city like Adelaide provides a variety of urban waste which can be re-introduced as plant nutrients via composting,” says Professor Cavagnaro.

“One community garden has now switched from horse manure to spent coffee grounds which they collect from local cafes. Coffee is much higher in nitrogen and can be used to counteract imbalanced soil nutrients.

“Urban agriculture can contribute to sustainable food production by reducing transportation routes and food imports, which in turn contributes to a reduction in greenhouse gas emissions. It helps ‘close the loop’ on waste, improves the environment and is efficient use of land in densely populated areas.”