Submitted to: Centre for Agriculture and Biosciences International
Publication Type: Book / Chapter
Publication Acceptance Date: 9/2/1996
Publication Date: N/A
Interpretive Summary: Phosphorus (P) is an essential element for plant growth and its input has long been recognized as necessary to maintain profitable crop production. Phosphorus inputs can also increase the biological productivity of surface waters. Thus, reducing P loss in runoff is of prime importance in minimizing accelerated eutrophication of fresh waters. More intensive crop pand livestock production in many parts of the world, has generally increased the potential for P export from watersheds. Thus, a greater understanding of where P is coming from, how much P in soil and water is too much, and how and where can we reduce these losses and inputs, is needed to develop economically and environmentally sound P management systems. To define targets for reduced losses, we must first identify critical or acceptable levels of P in freshwater bodies, depending on the biological response as well as use of the water. Identification of critical sources of runoff, erosion, and high P soils in a watershed is critical to effective targeting of remedial strategies that reduce P export. Even so, we have not been successful at translating this basic knowledge to implementation of management programs that are both effective and practical to farmers. In many areas, participation in such programs is still voluntary, thus, we must continue to emphasize interdisciplinary research to highlight the economic and environmental benefits of remedial programs. This should also include programs to overcome the public's common misconception that it is often much cheaper to treat the symptoms rather than sources of eutrophication.
Technical Abstract: Although inputs of phosphorus (P) are essential to productive agriculture, its export in watershed runoff can accelerate the eutrophication of receiving fresh waters, creating serious local and regional economic problems. Agriculture now contributes a greater share of fresh water inputs of P than 25 years ago. Thus, increasing pressures are being put on nagricultural systems to sustainably utilize P in animal manures and off-fa tes. Long-term applications of P as fertilizer or manure, at rates continuously in excess of crop removal, have resulted in soil P accumulations that are of environmental rather than agronomic concern. Moreover, current P inputs in feed and manure to agricultural systems often maintain high soil P levels or result in small and slow declines in soil P at best. Thus, remedial strategies must consider more than reducing P inputs. Options include decreasing transport potential by targeting critical source areas of both runoff and P. For example, less than 10% of watershed area and annual flow often contributes as much as 90% of P exported annually. Other options are more efficient harvesting and removal of soil P in farm produce, finding alternative off-farm uses for manure, and development of protocols to identify and target sustainable resource management systems. This review discusses the general role of agricultural P management in accelerated eutrophication and where our lack of information limits improved P management.