From fertiliser to Zyklon B: 100 years of the scientific discovery that brought life and death

[NickB79]

3. Manure has to come from somewhere

The most powerful natural fertilizers are animal manures. To get animal manure, you need livestock. And, to raise livestock, you need to devote a fairly large portion of your land to growing food for the livestock. Pasture, hay for winter feed, some grains, etc. And to do so sustainably, you can't overstock your pastures and let them eat it to dirt. That means far less land to grow crops on, and while livestock does produce food, crops produce far more per acre. You can feed a lot more people with 100 acres of grain than you can with 50 acres of grain and 50 acres of pasture.

So, why do farmers raise livestock in the first place? In large part because millenia ago, farmers figured out they needed to use crops, rotation, and livestock to create balanced soils. Many soils can't produce for long with just crop rotation and green manures; animal manure was vital. With the introduction of artificial fertilizers, they were able to cut out a previously vital step and drastically boost the amount of land available for crops.

Also, it goes much better with the modernized, mechanical way of farming than the old, family farm style that is dying out. It's easier to farm 1,000 acres with simple-to-apply chemical fertilizers than with heavy, cumbersome composts. Even the Chinese, who pioneered the use of "night soils" and intensive farming, are rapidly switching over to the US way of industrialized farming