The energy input is the sun, and most of the calories come from the air (carbon dioxide). Given so much external input, harvesting from a plot without reducing soil fertility is totally possible. With nitrogen-fixing crops (soybeans being the poster child), even the nitrogen fertilizer comes from the air.
The energy input is the sun, and most of the calories come from the air (carbon dioxide). Given so much external input, harvesting from a plot without reducing soil fertility is totally possible. With nitrogen-fixing crops (soybeans being the poster child), even the nitrogen fertilizer comes from the air.