Comparing Food Production Systems: Inputs, Outputs and Energy Efficiency

Systems thinking applied to a farm. A food production system can be described by its inputs (energy, labour, water, fertiliser, seed, machinery), its outputs (food, but also waste, runoff and emissions), its internal transfers and the efficiency with which inputs become outputs. Comparing two systems is a matter of putting numbers on those flows and then — the part that scores — choosing the right measure to compare them by.

Two contrasting systems. A subsistence, labour-intensive system such as wet rice in South-East Asia uses human and animal labour, manure, saved seed and rain or canal water; inputs of roughly 500 MJ per hectare produce about 3 tonnes of rice, some 6 000 MJ of food energy — an energy ratio of about 12 : 1. Soil is maintained, wastes return to the field, crops are diverse and chemical use is low; but yield per hectare is modest, labour demand is high, a failed harvest is a famine, and there is little surplus to sell. A commercial, capital-intensive system such as North American maize uses machinery and diesel, synthetic nitrogen, pesticides, hybrid seed and pumped irrigation; inputs of about 30 000 MJ per hectare produce around 10 tonnes, some 45 000 MJ — an energy ratio of only about 1.5 : 1. Yield per hectare and per worker is high and the surplus feeds cities; but the system depends on fossil fuels, erodes soil, leaks fertiliser into rivers, loses biodiversity to monoculture and leaves farmers in debt.

The measure decides the winner. Per hectare, the commercial farm yields three times more. Per unit of energy input, the subsistence farm is eight times more efficient. Per worker, the commercial farm wins by fifty times. Per tonne of soil lost or nitrogen leaked, the subsistence farm wins again. None of these is the "correct" measure; an evaluation states which is being used and for whom the system is supposed to be sustainable — the farmer, the urban consumer, or the soil and climate.

Livestock and diet. Feeding grain to animals adds a trophic level: about 7 kg of plant feed, 15 000 litres of water and a large methane emission go into 1 kg of beef, and roughly 90% of the energy is lost at the transfer. Livestock occupy most agricultural land while supplying a minority of calories. Shifting diets down the food chain is therefore the single largest lever on the land, water and climate footprint of food — larger than any change in farming method — which is why food questions so often end at the consumer rather than the farm.