We need to close the nutrient loop by returning animal and human manure back to the soils that fed them. It's not hard, just expensive. As Phosphorus becomes mo

We need to close the nutrient loop by returning animal and human manure back to the soils that fed them. It's not hard, just expensive. As Phosphorus becomes more expensive due to scarcity, our incentive to recycle it from animal and human excreta will grow until it reaches a tipping point where recycling all human and animal waste starts to become the more economical choice.