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Like other ecosystems, agroecosystems form partially closed systems in which animals, plants, microbes, and other living organisms and their environment are interdependent and regularly interact. They are somewhat arbitrarily defined as a spatially and functionally coherent unit of agricultural activity.Agro-ecosystem Health Project. 1996. Agroecosystem health. University of Guelph, Guelph, Canada.
An agroecosystem can be seen as not restricted to the immediate site of agricultural activity (e.g. the farm). That is, it includes the region that is impacted by this activity, usually by changes to the complexity of species assemblages and Food chain, as well as to the Nutrient cycle. Agroecosystems, particularly those managed intensively, are characterized as having simpler species composition, energy and nutrient flows than "natural" ecosystems.Elske van de Fliert and Ann R. Braun. 1999. Farmer Field School for Integrated Crop Management of Sweetpotato. Field guides and Technical Manual. Bogor, Indonesia: International Potato Center. . Likewise, agroecosystems are often associated with elevated nutrient input, much of which exits the farm leading to eutrophication of connected ecosystems not directly engaged in agriculture.Agroecosystem Management for Improved Human Health: Applying principles of integrated pest management to people. D. G. Peden. Published in New Directions in Animal Production Systems. Proceedings of the Annual Meeting of the Canadian Society of Animal Science, July 5–8, 1998, Vancouver, British Columbia, Canada. Edited by R. Blair, R. Rajamahendran, L.S. Stephens, M.Y. Yang.
Some major organizations are hailing farming within agroecosystems as the way forward for mainstream agriculture. Current farming methods have resulted in over-stretched water resources, high levels of erosion and reduced soil fertility. According to a report by the International Water Management Institute and the United Nations Environment Programme,Boelee, E. (Ed) Ecosystems for water and food security , 2011, IWMI, UNEP there is not enough water to continue farming using current practices; therefore how critical water, land, and ecosystem resources are used to boost crop yields must be reconsidered. The report suggested assigning value to ecosystems, recognizing environmental and livelihood tradeoffs, and balancing the rights of a variety of users and interests, as well addressing inequities that sometimes result when such measures are adopted, such as the reallocation of water from poor to rich, the clearing of land to make way for more productive farmland, or the preservation of a wetland system that limits fishing rights.Molden, D., Opinion: The Water Deficit, The Scientist, 23 August 2011
One of the major efforts of disciplines such as agroecology is to promote management styles that blur the distinction between agroecosystems and "natural" ecosystems, both by decreasing the impact of agriculture (increasing the biological and trophic complexity of the agricultural system as well as decreasing the nutrient inputs/outflow) and by increasing awareness that "downstream" effects extend agroecosystems beyond the boundaries of the farm (e.g. the Corn Belt agroecosystem includes the hypoxic zone in the Gulf of Mexico). In the first case, polyculture or Buffer Strips for wildlife habitat can restore some complexity to a cropping system, while organic farming can reduce nutrient inputs. Efforts of the second type are most common at the Drainage basin scale. An example is the National Association of Conservation Districts' Lake Mendota Watershed Project, which seeks to reduce runoff from the agricultural lands feeding into the lake with the aim of reducing algal blooms.TMDL Case Study: Wisconsin
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