1. How energy efficient are agroecosystems? Agricultural Energetics

2. Agriculture Energetics
The ultimate energy input in agriculture is the Sun – it powers the plants, the fertiliser and even the tractors!
Look at the following list of energy inputs into a farm in Norfolk:
• Diesel for tractor
• Nitrate fertiliser for wheat & peas
• Human labour
How can these be classed as indirect solar energy?

3. Agriculture Energetics
Energy Input
Why is this solar energy ?
Diesel for Tractor
Sunlight -> photosynthesis -> dead marine plants -> oil -> diesel
Nitrate fertiliser for peas
Sunlight -> photosynthesis -> animals fed on plants -> coal= dead animals -> burn in power station -> fertiliser made in Haber process
Human Labour
Sunlight -> photosynthesis -> animals fed on plants -> humans eat animals

4. Productivity & efficiency
Farmers try to maximise productivity and efficiency but they aren’t the same thing.
Productivity = yield/unit area
Efficiency = yield/unit of input
Yield = volume of milk/weight of meat/weight of crop harvested etc
Inputs = capital, labour, fuel, fertiliser etc
Agroecosystems need energy subsidies in the form of fossil fuels

5. Agricultural systems may be intensive or extensive

6. Intensive or Extensive?
Market gardening in Holland
Growing wheat in Australia
Sheep farming in the Lake District
Arable farming in South East England.

7. Fossil fuels
The most productive farms are often the least efficient as the high productivity is achieved by proportionally greater inputs e.g. of e.g. fossil fuels in the form of artificial fertilisers/machinery
Fossil fuels thus = a huge energy subsidy
Fossil fuels are finite, thus agriculture in MEDCs is unsustainable
In MEDCs fossil fuels usually make up between % of total energy inputs (fertilizer& pesticide manufacture, transport and application, machinery etc).

8. Energy Ratios Amount of energy got out (Crops/Beef/Eggs/Rape/Oil)
Amount of energy put in (Sunlight/Diesel/Electricity etc)
Energy Ratio =
10.0
60 tropical crops- subsistence
5.0 tropical crops
0.38 milk production UK
100
4.20 sugar beet UK
1.75 potatoes UK
1.0
0.90 peas UK
0.14 battery eggs UK
0.1
0.01
0.04 Fishing Fleet UK
Energy ratios for food crops & agricultural systems
If we get exactly the same amount of energy out as we put in, the ratio would be 1.
If we got out 10 units of energy but we put in 20, we would have a ratio of ½ = 0.5
These are >1. Does this mean that we actually can get more energy out than we put in? No. It means the figures ignore huge inputs e.g the energy from the Sun, transport and processing inputs.

9. Energy Ratios
10.0
60 tropical crops- subsistence
5.0 tropical crops
0.38 milk production UK
100
4.20 sugar beet UK
1.75 potatoes UK
1.0
0.90 peas UK
0.14 battery eggs UK
0.1
0.01
0.04 Fishing Fleet UK
Energy ratios for food crops & agricultural systems
Bayliss-Smith (1982) calculated the energy ratio of English agriculture for 1826 and 1971:
1826: 40.3
1971: 2.1
The energy ratio has declined greatly over the150 years
Output has, in fact increased, but inputs have increased much more
In the UK and other MEDCs fossil fuels = % of total energy inputs

10. Questions
For each of the suggestions below, explain how this would make agriculture more sustainable.
1. Increase government funding for organic agriculture 2. Retrofit agricultural machinery to run on biodiesel 3. Encourage vegetarianism 4. Promote local farmers markets 5. Introduce legislation forcing supermarkets to show air miles on products.
In the exam, you may be asked to:
1. Explain why agriculture is energy-subsidised
2. Explain why modern agriculture is unsustainable
3. Calculate and compare energy ratios for selected countries
4. Suggest ways in which agriculture can be made more sustainable