It's in part a cycle -- land to humans to waste to land. Only in part as nitrogen can oxidize to go back to the air, so it needs to get fixed again by bacteria.
Actually, you excrete most of your nitrogen through kidneys. Pig/human dung contains just 0.3% of nitrogen by weight. Anyway, you can read historical data - human waste is not enough, even using it for compost required to lay fields fallow one year out of three or four (depending on location).
"Fertilizer Runoff Overwhelms Streams and Rivers--Creating Vast "Dead Zones" The nation's waterways are brimming with excess nitrogen from fertilizer--and plans to boost biofuel production threaten to aggravate an already serious situation"
That's because the total amount of fertilizers used is huge. Very little of it is lost, but even that can cause trouble.
What that shows is that alternatives have worked. China is one of the most densely populated places on the planet. If they could do it, it shows the US could do it and other countries could do it.
It was not nearly the most densely populated place (England was) before the 20-th century. China was pretty average compared to European countries.
Still, you can't compare what you presumably had to do with limited tools and limited materials and limited information in a (probably) limited climate on impoverished soils with what is really possible with good tools, abundant materials, abundant information, in a good climate on well prepared soils.
We had lots of information, good enough manual tools and adequate soil. It still takes A LOT of labor if pesticides are not used. Real industrial farming is way more economic and might actually be _healthier_ for the environment, because pesticides allow no-till agriculture.
I see. I'll try not to assume that context might explain a lot.
I certainly studied the organic farming including the 'Holistic' book. It's pretty much the same story as alternative medicine vs. actual medicine - the parts of alternative medicine that work simply become medicine. I've also studied the opposite opinions that pure organic farming is not sustainable and so far it definitely looks like it.