The food and agriculture system is among the largest anthropogenic activities in terms of appropriation of land and biological primary production, as well as alteration of the grand biogeochemical cycles of carbon, water, and nitrogen. Despite its importance in these respects, physically coherent descriptions and analyses of the food and agriculture system regarding the total turnover of fundamental flows (such as biomass) and resource use and efficiency of critical processes (such as animal food production) are relatively scarce.
This article presents a survey of the current flows of biomass in the food and agriculture system. The survey gives a mass‐ and energy‐balanced description of biomass from its production on cropland and grassland through its transformations into animal and vegetable food products to its final conversion into respiratory heat, feces, and other residues. This assessment was carried out by means of a physical model that, for eight world regions, calculates the necessary production of crops and other phytomass (plant biomass) from a prescribed end use of food, efficiency in food production and processing, and use of system‐internal by‐products and residues as feed, feedstock, and food.
The global appropriation of terrestrial phytomass production by the food system was estimated to be some 13 Pg (1.43 × 1010 short tons) dry matter, or 230 EJ (2.18 × 1017 Btu) gross energy (higher heating value), per year in 1992‐1994. Of this phytomass, about 8% ended up in food commodities eaten. Animal food systems accounted for roughly two‐thirds of the total appropriation of phytomass, whereas their contribution to the human diet was about 13% (both on a gross energy basis). The ruminant meat systems were found to have a far greater influence than any other subsystem on the food system's biomass metabolism, primarily because of the lower feed‐conversion efficiency (calculated as carcass produced by total feed intake, including pasture and other human‐inedible feedstuffs) of those systems.
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Metabolism of Cities