Agricultural energetics

• The intensity of agriculture is a measure of the amount of artificial inputs and the extra yield that is produced.
• In extensive agriculture, the aim is to maximise the total yield by spreading the available inputs over a large area of available land.
• Intensive agriculture is practised where large inputs are available but there may be a shortage of land. Yield per unit may be high but extra yield per unit of input may not be.
• Major agricultural energy subsidies include: manufacture of nitrate fertilisers; manufacture of pesticides; pumping of irrigation water; fuel for machinery for ploughing, spraying, harvesting; energy for the manufacture of machinery and equipment; heat for drying harvested grain; processing of food for consumers; transport of food to consumers.
• As agricultural systems have become more productive and more intensive, they have become increasingly dependent on energy subsidies, especially energy from fossil fuels. It may be difficult to maintain or increase food production if abundant energy supplies cannot be maintained.
• The energy ratio is a measure of efficiency by comparing energy inputs and outputs and then expressing this as the number of units of food energy produced per unit of energy input. Systems that give the highest yields per unit of energy input have higher energy ratio values.
• Energy ratio is not the same as productivity per unit area. A system with a high productivity may require high energy subsidies and therefore have a low energy ratio.
• The food conversion ratio is a measure of the mass of food needed to produce a given mass of livestock growth. The lower the ratio, the better the conversion of food into animal biomass.
• Autotrophic nutrition is when chemicals are broken down to release this energy are not generally available in the environment but can be built up from simpler molecules by autotrophs. Autotrophs use their energy to make carbohydrates and lipids. Photo-autotrophs capture sunlight for photosynthesis. Chemo-autotrophs harness energy by oxidising substances. Autotrophs have a big advantage for survival as they don’t rely on other organisms for their energy supplies.
• Heterotrophic nutrition is when organisms can’t produce their own high-energy molecules must gain their energy from other living organisms. The amount of energy available to heterotrophs is less than what was harnessed by the autotrophs.
• The amount of energy in a food chain declines with each progressive trophic level, the amount of food that can be produced by an agricultural system depends upon which trophic level produces the food. The most productive agricultural system would be plant blasted as less energy is lost through trophic levels.
• energy efficiency = energy input/energy output x 100