Nutrient recycling on humanity's menu

The ability of humanity to feed itself through the steepest increase in food demand in history lies in something most communities throw away: nutrients.

In the next 40 years, according to the UN Environment Program, world food output must rise 110 per cent to meet the demands of population growth and improving diets in places such as China, India and Latin America.

This will require more food yearly than has so far been produced in the whole of history. Yet ponder the following of Australia's situation:

Of all the nutrients applied on our farms, up to half are wasted, in that they do not go to crops or pastures but are lost to soil lock-up, weeds, erosion, leaching or run-off. The industry that processes our food spends $750 million a year just to dispose of its waste. One-third to one-half of all the food that enters our shops, supermarkets, restaurants and homes is thrown away. Our cities waste 97 per cent of their sewage effluent and its nutrients.

If these estimates are sound, in theory it is possible to feed an extra 30 million to 60 million people on an Australian diet with the nutrients we presently chuck into landfills and the ocean.

Recent drought has made Australians more conscious of the need to be sparing in our use of water, but there is hardly public discussion of reusing that which supports all life: nutrients.

We are the most prodigal generation there has been. Our great-grandparents, who carefully forked their compost heaps and manured their fields, would consider a society that buys new nutrients each year, then throws them away, to have lost its reason.

The world supply of nutrients is not yet critical, so why worry? In the past 30 years, the price of fertiliser has risen by an average 1,000 per cent: about twice the rate of oil price increases. What's going to happen in the next 40 years when world food output has to more than double?

Nutrients may become expensive and even scarce commodities, especially as some of them are being used to grow transport fuels and therefore replace oil.

Australia has an excellent record in learning to manage nutrients on farms. The dairy industry in particular has done much pioneering work on the nutrient cycle to minimise the loss of nutrients down the creek. CSIRO has done good work on the reuse of sewage nutrients to grow things, and Melbourne Water likewise, yet most of our nutrients are still trashed.

Work on recycling food waste from processing, retailing or end consumers has hardly begun. US environmental scientist Peter Raven recently remarked that humans use or destroy 45 per cent of all terrestrial bioproductivity. If he's even close to right, there is going to be colossal demand for nutrients in the coming decades.

Australia, a lean and hungry continent, could distinguish itself by becoming the first nation to seriously attempt to close the nutrient loop, to reuse our nutrients again and again before they finally make their way to the deep ocean.