Independent Consultant, Germany
Some vegetarians (e.g. H. MAUCHER, chef of Nestlé until 1997) believe that consuming animal products including milk is an intolerable waste of global food supply. The objective of this study was to compare the efficiency of converting crop biomass into human food by using the biomass either as forage for milk production or as green manure for grain production as it is practised in stockless organic farms. Feed energy conversion efficiency for milk production was calculated with data from published experiments with Holstein dairy cows in Bavaria (including heifer production) and with standard metabolic efficiency values. The food grain production efficiency of green manure and animal manure was calculated in carbon (C) units using published field and laboratory experiments in temperate regions. The results were calculated for 100kg biomass C: If 100kg C are applied as green manure on a grain crop with a 50% harvest index, grain yield increases by 9kg C. Feeding 100kg forage biomass C to dairy cows produces an amount of animal manure that is equivalent to 79kg green manure C, because soil accumulation of animal manure is 2.5-times higher than of green manure. This amount of animal manure application improves grain yield by 7kg C. In addition, the digested fodder C fraction (60%) is converted to 20kg milk C at 34% efficiency. Thus the dairy system transforms biomass 3-times [(20+7)/9] more efficient into human food with a higher economic value than the vegetarian system with green manure application. Using tropical data in the same calculation, the dairy system with an energetic efficiency of 20% transformed biomass 2-times more efficient into food than the vegetarian system. To conclude, a vegetarian diet may convert less crop biomass into human food than a diet that includes also milk if some crop biomass is required for green manure application to substitute for animal manure.
Keywords: Animal manure, carrying capacity, green manure