Types Of Energy Used In Agriculture

Solar energy

Agriculture is one of the biggest users of solar radiation. Solar energy is used directly by plants through the process of photosynthesis; 90% of a plant's requirements for growth are provided by solar energy, the other 10% being water and nutrients. The muscle power of humans and animals is derived from the food they eat, which has been produced in large part by the sun's energy; the solar energy of the past is stored in fossil fuels composed of millions of years worth of decomposed and compressed plant material; wind and water power are indirect forms of solar energy because wind and rain result from temperature differences brought about by the sun.

The process of photosynthesis is at the heart of agriculture since all crop production for human consumption and the production of food for animals is almost completely dependent on photosynthesis, directly or indirectly. Plants use solar radiation to fix carbon in the process of photosynthesis. However, not all of the solar radiation can be used in this process; in fact, very little of the total light received by plants is ever used and about a quarter of the visible light is reflected. Of that absorbed, most is converted to longwave radiation and remitted or used in the evaporation of water in transpiration. (refer to soil and water conservation, in the hydrologic cycle section). On average, about 22,000 kW of energy are received per hectare each day but less than 2% of this is generally used for photosynthesis and for heating and cooling the soil. (Spedding, 1996)

Thus, the full exploitation of light requires a more complex reception surface than a single horizontal layer, and plants exhibit a great variety of ways of arranging their leaves to best advantage. Also, the rate of production is usually limited by other factors such as temperature, water supply, soil fertility, and incidence of pests and diseases. These can be manipulated and controlled by the farmer to a varying degree, and this often involves the use of complementary sources of energy.

Animal power and human labour

For most of the time that humans have inhabited the earth, their prime source of power has been their own muscles and the ones of domesticated animals. Muscle power is still used in many developing regions to carry goods, to till the land, to mill cereals, to plant, cultivate and harvest crops. Since about 1945 farming became widely mechanized in the western part of the world and extensive use of fertilizers and pesticides really got under way; with traditional forms of manual labour and animal power being put aside. Mechanization using fossil fuels (coal, petroleum, natural gas) by-passes the limits of human labour in agriculture, and that is the rather small area that one person can cultivate, weed, harvest, etc. Animal power greatly increases the area that can be worked, but part of that has to be used to feed the animals, and tractors and associated machinery can cope with very much larger areas in much faster time.

The only ways in which it would be economical for the farmer to go back to manpower would be to make fossil fuels tremendously more expensive; likewise, a return to horsepower would be just as uneconomical, and would seriously jeopardize the ability to feed the number of people living on the earth today. The horse needs feeding all year round but tractor needs fuel only when it has a job to do. At current prices for farm produce, farmers cannot afford to devote about15% of the land to feeding horses and oxen and it is much more financially efficient to buy a tractor and to increase income by using the land area saved to grow extra crops for sale.

The fact that it has been financially profitable for farmers to employ fossil fuel energy in agriculture, either directly or indirectly, has had a profound effect on manpower requirements and on crop yields per hectare, and, consequently, on the total amount of food produced. Since the introduction of mechanization to Canadian farming approximately 100 years ago - successively by steam, petroleum and electricity-driven equipment - the number of farmers has fallen from 75% to just 2% of the population. For the first time in history, the population of western nations have been able to increase while the amount of cultivated land has fallen.

Complementary energy sources

In the developed countries, agriculture uses substantial amounts of fossil fuels, the principal type of complementary energy, in the production and use of fertilizers and machinery. For example, one ton of atrazine, a pesticide used extensively in corn production, requires 190 GJ of energy for its production while the energy input required by a 65 h.p. (48.5 kW) tractor is 230 MJ/hr. Plowing at a depth of 0.2 m consumes 1180 MJ/ha while baling hay consumes about 295 MJ/ha. (Green, 1978)

In fact, modern agriculture practices would not be possible without the use of fossil fuels. But why the expression 'complementary energy' while talking about fossil fuels? Fossil fuel energy cannot usually be converted into food energy, although it can influence the rate of food production. For example, fertilizer may promote greater crop growth and enhance food production, but the energy in or used to manufacture the fertilizer does not appear in the product. This is why it is called 'complementary' energy: it supports and facilitates production but it is not part of the energy production conversion process. The inputs of complementary energy vary with the product, but it must be born in mind that the energy output ('in' the product) is not derived from the complementary energy used.