Agricultural ecosystems are made up largely of domesticated animals and plants used to produce food. There are considerable energy losses at each trophic level.
This means that the energy we receive from the food we eat is often only a tiny proportion of that available from the sun at the start of the food chain.
Agriculture tries to ensure that as much of the available energy from the Sun as possible is transferred to humans.Productivity
Productivity is the rate at which something is produced.
The rate at which plants assimilate chemical energy from the sun is called gross productivity. It is measured for a given area over given period of tie.
Usually in the units: kJ m-2 year -1 .
Some of this chemical energy is utilised by the plant for its respiration.
The remainder of this is known as the net productivity.
This is available to the next organism in the food chain.
Net productivity is important in agricultural ecosystems and is affected by two main factors:
- The efficiency of the crop at carrying out photosynthesis this is improved if all the necessary conditions for photosynthesis are supplied
- The area of ground covered by the leaves of the crop
To maintain an agricultural ecosystem, we have to prevent a climax community developing. We do this by excluding most of the species in that community, lea
ving only the particular crop that we are trying to grow.
To remove or supress the unwanted species and to maximise growth requires an additional input of energy.
This energy is used to plough fields, sow crops, remove weeds, supress pests and diseases, feed and house animals, transport animals and many other tasks.
This additional energy comes from:
Farmers and other people that work on farms expend energy as they work This energy comes from the food they eat
As farms have become more mechanised, energy has increasingly come from the fuel used to plough, harvest and transport crops, to produce and apply fertilisers and pesticides and to house, feed and transport crops