Everything we eat can be traced back to the Sun. Sunlight powers plant photosynthesis, which yields the grains that we eat in bread, cereal, and rice. Plants feed the animals that provide us with beef, pork, and poultry. And the fishes of the sea feed on tiny phytoplankton that photosynthesize in the upper layers of the ocean’s waters.
A group of ecologists at the University of Montana asked the question: do croplands create more or less new plant biomass than the natural ecosystems they replace?
Earlier work reported that irrigated and fertilized crops generate 10% more plant growth than the grasslands they replace. But, without those subsidies, agricultural productivity is lower than that of nature. When croplands replace tropical rainforest, the generation of new plant biomass can be diminished by as much as 71%.
When we cultivate, irrigate, and fertilize crops, we replace some of nature’s work with our own. For instance, nitrogen is readily cycled from live plants to soil decomposers and back to live plants. Break that cycle, and you need to apply fertilizer to keep the soil nitrogen at optimum levels. But of course, fossil fuels are required to produce fertilizer. In a very real sense, we are replacing the natural process of decomposition with an artificial process—an energy subsidy that makes up for our destruction of nature.
Agriculture is very efficient at converting sunlight into crops that feed humanity. But without subsidies, plant growth is less efficient in agriculture than in natural lands. Next time you have a bowl of corn flakes, remember that part of what you eat is derived from the energy of fossil fuels.
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Photo, taken April 26, 2009, courtesy of Ivy Dawned via Flickr.
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Earth Wise is a production of WAMC Northeast Public Radio. Support for Earth Wise comes from the Cary Institute of Ecosystem Studies in Millbrook, NY.