107. MANURE CALCULATIONS

In 2001/2002, the breakdown of fertilizer consumption in the U.S. was:
Nitrogen: 10.9 million metric tons (MMtonnes)
Phosphorus: 4.2 MMtonnes
Potassium: 4.5 MMtonnes (Source)

The following Table comes from a report by the Stockholm Environment Institute called "Guidelines on the Use of Urine and Faeces in Crop Production" Source(pdf), P. 6
In 2002, the population of the U.S. was about 288,000,000 (source: New York Times Almanac, 2004). Therefore, calculating from the Chinese values, the total fertilizer production in the U.S., per year, in the form of human urine/faeces is roughly:
Nitrogen: 1.1 MMtonnes
Phosphorus: .17 MMtonnes
Potassium: .5 MMtonnes

Percentages of total U.S. fertilizer use which could be supplied with human urine/faeces are thus:
Nitrogen: 10%
Phosphorus: 4%
Potassium: 11%

Now let's turn to the figures for livestock waste (click to enlarge).
Source
Fertilizer in livestock waste, per year, in the U.S. is roughly:
Nitrogen: 5 MMtonnes
Phosphorus: 1.3 MMtonnes
We can also get the following ballpark figure for potassium, assuming that animal waste contains 3 times as much potassium as phosphorus (as is the case for humans):
Potassium: 4.1 MMtonnes

Manure from humans + livestock can thus compensate for the following percentages of chemical fertilizer consumption:
Nitrogen: 56%
Phosphorus: 43%
Potassium: 102%

This is pretty good, although there are clearly a lot of leaks in the system which allow nutrients to escape the cycle. These include:
1) Run off waste (nutrients flowing into water)
2) Escape of volatile nitrogen into the air (ammonia)
3) Human carcasses which are not composted
4) Animal parts which are not composted (bones, blood, hides, teeth etc.)
5) Kitchen/yard/garden wastes buried in land fills
6) Food exports etc.