Agricultural Energetics

The intensity of agriculture is the amount of artificial inputs and extra yield.

Extensive agriculture: maximise total yield by spreading available inputs over large areas of available land

Intensive agriculture: large inputs available but shortage of land. Very productive but not very efficient.

The Law of Diminishing Returns: each extra unit of input causes the yield to increase, but by a smaller amount than previous inputs.

How can we apply the law of diminishing returns to the global food production system?

We redistribute inputs from intensively farmed areas to extensively farmed areas.

  • This would cause the total yield to increase.
  • Most uneven inputs are due to economic reasons, as poorer communities have poorer access to these resources.

Energy Subsidies

Energy subsidies, or inputs, are any input that aid productivity but require the use of energy.

There are two types of energy subsidy:

  1. Direct energy subsidies - used on the farm
  2. Indirect energy subsidies - used elsewhere, to make the input

Examples

  • Manufacture of nitrate fertilisers
  • Manufacture of pesticides
  • Pumping of irrigation water
  • Fuel for machinery (for ploughing, spraying, harvesting…)
  • Energy for manufacturing machinery and equipment
  • Heat for drying harvested grain
  • Processing of food for customers
  • Transport of food for customers

Energy Ratios

  • Energy ratio: a measure of efficiency comparing energy inputs and outputs and expressing this as the number of units of food energy produced per unit energy input
  • The higher the energy ratio, the better

Food Conversion Ratios

  • Food Conversion Ratio (FCR): A measure of the mass of food needed to produce a given mass of livestock growth
  • Lower ratio → better conversion of food to animal biomass

Productivity

  • More of an economist's measure
  • Productivity = Output (MJ) / Area (ha)
  • The units can vary but MJ and ha are typical for productivity.
  • Higher = more productive (more intensive)

Energy Efficiency

  • More of an environmental scientist's measure
  • Energy ratio = edible energy output (MJ/ha) / energy input (MJ/ha)

Control of Food Chain Energy Losses

Autotrophic Nutrition

  • All living organisms need chemical energy to drive biological metabolic processes
  • The chemical broken down to release this energy are not generally available in the environment
    • Instead, they can be built up from simpler molecules by autotrophs (mostly photoautotrophs, others are chemoautotrophs).
    • Source of energy needed to build up high-energy molecules, e.g. carbohydrates (glucose, starch, cellulose), lipids (fats, oils).

What are autotrophs?

  • Autotrophs are "self-feeders"
  • They have a big survival advantage, as they don't rely on other organisms for energy. All other organisms rely on autotrophs for energy supplies.
  • Photoautotrophs capture sunlight during photosynthesis, and include plants, algae, and photosynthetic algae
  • Chemoautotrophs include bacteria that harness energy by oxidising substances like hydrogen sulfide, methane, ions of ammonium & nitrate…

Heterotrophic Nutrition

What are heterotrophs?

  • Heterotrophs are "different-feeders", including all animals, fungi, and many bacteria
  • Organisms that cannot produce their own high-energy molecules must gain energy from other living organisms
  • Much of the energy captured by autotrophs is used in metabolic processes and released back to the environment as heat
    • This means less energy is available to the heterotrophs than was harnessed by the autotrophs
    • It follows, then, that less energy is transferred with each successive trophic level in a food chain
    • This is also why food chains don't often have more than four trophic levels.
    • Hence, the amount of food produced by an agricultural system depends on the trophic level that produces the food.
    • Generally, more plants can be produced in an area than meat.
      • With the exception of areas that cannot grow crops that can be eaten by people (e.g. upland areas or semi-arid areas).
      • Omnivores like pigs can also produce food from food wastes not wanted by people.