As we deplete our reserves of mined phosphorus, will sewage sludge be the only way to feed ourselves?
By Amanda Kimble-Evans
Nitrogen, potassium and phosphorus. These three key nutrients are part of the foundation on which growing food is intimately reliant and is the basket in which the disciples of reductionist industrial agriculture have put all their metaphorical eggs. Phosphorous, specifically, is the focus of a recent report from the Soil Association that warns of a coming crisis, “Without fertilization from phosphorus it has been estimated that wheat yields could fall from nine tones a hectare in 2000 to four tones a hectare in 2100.” According to the report, the availability of mined phosphorus could even peak in the next 30 years.
What is the answer? The Soil Association offers a number of recommendations, focusing much of their effort on increasing the use of human waste as a fertilizer for farm fields both nonorganic and organic.
The real beef with biosolids
Treated human waste (otherwise known as sewage sludge or biosolids) has been indicated as a risk to human and environmental health for a multitude of reasons. The report addresses the heavy metals found to be problematic in the past, stating the levels have been declining in recent years. But, it does not, admittedly, discuss the more recent red flags such as antibiotics, hormones, steroids and other pharmaceuticals, or things like triclosan, flame retardants and solvents that end up poured down drains.
Researchers at Virginia Tech, for example, recently warned that excreted antibiotics spread on farm fields are contributing to antibiotic resistant bacteria and are a serious environmental problem.
And sewage sludge is already sprayed on conventional farm fields across the U.S. and the U.K. The only sector of agricultural land restricted from using biosolids is that of certified organic farms. “While nutrient cycling and a closed-loop system are key principles of organic agriculture, lifting the restrictions on sewage sludge for these farms would have very little impact on reducing the use of mined phosphorus overall and could open the gate for a whole host of new problems,” says Mark Smallwood, executive director at the Rodale Institute.
Coming down from the edge
A clearer and more direct path towards a more sustainable agriculture, less reliant on mined phosphorus, does exist. The following recommendations were touched on in the report to a lesser extent, but have the potential to make a greater impact with less risk to human and environmental health.
Smarter management: Phosphorus has made the news more often for its part in the Gulf of Mexico dead zone and algea blooms in lakes across the country than for its scarcity. The overuse of synthetic fertilizers and poorly timed applications of raw manures and biosolids have let this mobile mineral slip from the soils that feed us and into the waterways wreaking havoc all along the way.
Changing how we farm: Organic farming prohibits the use of synthetic fertilizers, and focuses, instead, on manure, compost, bone meal, or cover crops to provide the majority of phosphorus needs, effectively stepping out of the race for more and more mined phosphorus. Organic practices also pay heed to nurturing the micro-organisms in the soil which help retain and make available more of the phosphorus that is applied.
Changing how we eat: According to the Soil Association report, it takes more than twice as much phosphorus to support a meat-based meal as does a vegetarian meal, so reducing the amount of meat consumed will reduce our reliance on mined phosphorus. And when meat is on the menu, choosing grass-fed livestock grazed on organically-managed pasture is the best choice.
The use of mined phosphorus at breakneck speeds is a warning of yet another weak and crumbling pillar on which our primary agricultural system rests. Luckily, the awareness of our addiction provides an opportunity to invest in more regenerative systems for managing our resources, growing our food, feeding ourselves.