Antibiotics and nitrogen fertilizers together account for the 20th century human population explosion. Antibiotics (and to some extent vaccines) vastly reduced

Antibiotics and nitrogen fertilizers together account for the 20th century human population explosion. Antibiotics (and to some extent vaccines) vastly reduced childhood mortality, and the increased human population got out of the famine cycle via increases in food production made possible with ammonium/nitrate fertilizers, which allow practices like double cropping. The breeding of crop strains capable of utilizing that extra nitrogen to maximize growth also had a significant effect. However, it's undeniable that much of the vast quantities of nitrogen fertilizer applied to fields over the past 100 years never made it into food crops, and just ran off into rivers and oceans. The whole process could be made vastly more efficient, but in the past there was no strong argument to do so, as natural gas was cheap and the fertilizer industry was bent on increasing sales. Technology wise, the robotic farmer might change everything - it can weed without herbicides, and also deliver precise amounts of fertilizer to individual plants, something 20th century mechanized agriculture was incapable of.