Could compost fight upcoming food shortages?

The world is tackling a shortage of food, a rising price of fertiliser, and an excess of carbon in the atmosphere. But what if there was a scheme that could help all three at the same time? Compost, the very same stuff forming in a heap at the bottom of your garden, is the centre of a new soil management scheme, dubbed the ‘precision compost strategy’, which is designed to see if compost use in large-scale agriculture could improve crop yield, soil health and divert bio waste from landfill where it generates harmful greenhouse gases. And perhaps even reduce agriculture’s reliance on mineral fertilisers as well. Susanne Schmidt, of the University of Queensland, has been speaking to Will Tingle, about how compost has been stacking up against the fertiliser competition.

Susanne - Well, the benefits really are higher yields and getting more organic carbon into soils. So we calculated that with such a global strategy we could deliver in some situations, huge benefits that in dry and warm climates soils that are acidic, or have a sandy or clay texture, that compost achieved up to 40% more yield than conventional practice using mineral fertiliser. But when we looked at it globally, so in other words all the soils and climates and crops, we estimated that designer compost would increase the production of major cereal yields by 4%, which is over 96 million tons of grain annually. And for comparison, this is about double the grain yield harvested in Australia in a good year. So it's a substantial amount. And then the other benefit is that such a strategy has the technological potential to restore about 19 billion tons of organic carbon and soil. And that is nearly a third of current top soil carbon, in the upper 20 centimetres of soil. And so we propose that compost really should become part of human's toolkit for reversing climate change.

Will - So would this new method be more cost effective than current compost management, If you can call it that?

Susanne - That's a good question, which we actually did not investigate in our study, but we can assume that some costs are reduced because less mineral fertiliser is used. But depending on how much compost is applied to fields, transport costs may be higher. And one would, however, also need to include environmental costs such as water pollution and greenhouse gas emissions from conventional fertiliser versus compost, but then also consider the cost of the waste going into landfill. And we have started to address this question now using economic tools.

Will - There are some concerns that creating compost can lead to a production of nitrous oxide, which is a potent greenhouse gas. Could this method of compost management that you're proposing lead to an increased amount of nitrous oxide in the atmosphere?

Susanne - That is a really good point and that's why we included nitrous oxide emissions in our global analysis because adding organic matter to soil in the presence of nitrogen has been shown to increase nitrous oxide emissions. But we did not find evidence that compost systematically increases nitrous oxide emissions over those derived from mineral fertiliser. But we didn't have quite as much data as we had for yield and soil organic carbon and it would be good to investigate this more. But what we did see when compost was blended, it was mineral fertiliser to nourish, for example, nitrogen demanding crops, which is part of the precision compost strategy. We found that higher efficiency ensued. So in other words, compost used more of the supplied nitrogen in such organomineral fertiliser combinations. And that means that less nitrogen is wasted and lost from soil and indirectly that may mean that also less nitrogen oxide is produced.

Will - This compost management system could increase food production by 4%. I think it said, so this is something that the world sorely needs. How realistic would it be to roll out this new strategy on a worldwide scale?

Susanne - Well, as an optimistic scientist and educator, I would say that it is entirely achievable. There is now a lot of interest in transforming waste to value, as part of the circular economy. And there are many organic waste that can be used for composting. So farmers can make their own compost using farm waste and manures, city councils can use organic waste from households and green spaces, and wastewater managers have bio-solids that can be composted.