Ultimately, to maintain ongoing soil fertility, we are faced with figuring out how to put as much material back into the soil as we drew out of it. We must offset soil losses by building up soil gains.
Soil losses: Losses to the system include the harvestable portion that we eat. In the industrial agribusiness system, crop chaff is burned or used for purposes other than restoring soil fertility (example: biofuels). Soil erosion is a great loss, which can be controlled with more-sustainable farming practices. Our humanure is another loss to the system; most of us have not yet learned the skills of (safely) processing this product to return it to abundant productivity.
Soil gains: In more-sustainable food production the crop chaff is returned to the soil via compost or mulching. Right now, we haul in material from other locations (with enormous expenditures of petroleum resources and greenhouse gas emissions) to build up our depleted soils. But with the end of cheap, abundant oil, this practice isn’t going to be possible for very much longer. We will have to learn to use any and all local materials that we have around.
Next section: "More compost"