> The phosphorus in commercial fertilizer comes from phosphate rock, a non-renewable resource, while nitrogen comes from natural gas and requires a lot of energ

> The phosphorus in commercial fertilizer comes from phosphate rock, a non-renewable resource, while nitrogen comes from natural gas and requires a lot of energy to produce. But, there’s an endless stream of renewable phosphorus and nitrogen available: yes, we’re talking about urine. Where do the authors imagine the phosphorus and nitrogen in urine originate?