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In the last 10,000 years, our ancestors have altered the natural ecosystems only slightly. However, scientific and technological development have paved the way to drastic changes in contemporary ecosystems. As a result, much land has been converted into agricultural and cattle farms. Vegetation that was originally propagated only by falling seeds is now cultivated by humans as crops in agricultural fields.
Large areas of the Earth's land surface have been strongly impacted by humans through intensive agriculture, grazing and timber cutting. Current extensive logging in forest biomes and the conversion of natural grasslands resulted in the destruction of natural habitats of numerous species. Grassland teaches us about the impacts of human activities more than any other biome. The majority of the original grasslands have been converted into agricultural farmlands. These farmlands have become the 'granaries of the world'. Widespread agricultural and industrial development are depleting natural resources and also modifying natural ecosystems.
In the biosphere, among human made ecosystems, the largest recognizable units are the agricultural biomes. In terms of structure and function, agricultural biomes are very simple. They usually consist of one genetic strain of one species. Agricultural crops are short and group together to resist the cold temperatures and are protected by the snow during the winter. They can also carry out photosynthesis at low temperatures and low light intensities.
Agricultural biomes are overly sensitive to attack by one or two well-adapted insects that can multiply very rapidly to take advantage of an abundant food source. Thus pesticides are constantly needed to reduce insect populations. Weeds, too, are a problem and they can divert much of the productivity to undesirable forms. Herbicides are often the immediate solution to these problems. Application of agricultural chemicals is one of the ways that humans use energy inputs to increase net primary productivity. Large increases in productivity are achieved by application of nutrient elements and compounds, usually of nitrogen and phosphorus that are in short supply in most soils.
In a natural ecosystem, these elements return to the soil following the death of the plants that store them. In agricultural ecosystems, this recycling is interrupted by harvesting the crop for consumption. Therefore nutrients are added each year in the form of fertilizers, and these are mined from fossil fuels. The input energy humans add to the managed ecosystems in the form of agricultural chemicals and fertilizers, as well as farm mechanization, boost greatly the net primary productivity of the land. The net productivity of a particular crop increases more than five times over through two types of energy inputs.
a. Natural Energy Inputs: Sunlight serves as the main source of natural energy in all ecosystems. In agricultural ecosystems photosynthesis from the sun's energy, carbon dioxide in the atmosphere and rainfall are 'free' inputs. But, in order to be delivered to humans or animals for consumption, the raw food or feed product of this system requires fossil fuel energy.
b. Cultural energy: Excluding the solar energy of photosynthesis, the energy inputs expended upon production of food crops are referred to as Cultural Energy. They are:
Let us examine this with an example. The research undertaken by Dr.Norman Borlaug and his co-workers has succeeded in bringing a dwarf wheat variety with strong stems. The new wheat moved Mexico
into the ranks of a wheat exporting country. Tried out in Pakistan and India, the new wheat increased the yield per acre. Dr.Norman Borlaug, leader of green revolution was awarded the Nobel Peace Prize. The green revolution spread next into improvement of rice yields, carried out at the International Rice Research Institute in the Philippines. Drawing more than 20,000 varieties of rice, new highly productive strains were developed and passed onto rice farmers.
Water conservation techniques can greatly reduce the problems arising from excess water use. The most efficient way to water crop is drip irrigation. In drip irrigation, a series of small perforated tubes are laid across the field at or just under the surface of the soil. The tubes deliver the amount of water that each plant needs, directly onto its roots where the water will do the most good, and with a minimum of evaporative loss or over soaking of the soil.
So, crop productivity is determined by the amount of input energy supplied to an agricultural ecosystem. In an agricultural ecosystem a variety of crops are cultivated and harvested for consumption at a distant location. These crops are consumed as food products such as grains, flours or as processed food items. The solid, abiotic part of this system provides the raw materials and the supporting surface on which many of the processes of life depend.
By now you recognize the Earth and its biosphere make up complex, interactive system. The Earth system is sometimes compared to the human body. We are interested in how well our heart/lungs/muscles/nerves work, but we are most keenly interested in how well the components work together. So that we can improve our overall health. Similarly, the Earth has lithosphere, hydrosphere, atmosphere and biosphere as its component. Our health depends on how well our body interacts with its components. Likewise, the earth depends on its components and their interactions with each other. In the next lesson, let us investigate how to manage this interactive system and as well as planning for a sustainable future.
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