Tuesday, August 3, 2010: 4:20 PM
334, David L Lawrence Convention Center
Meagan E. Schipanski, Department of Plant Science, The Pennsylvania State University, University Park, PA, Elena M. Bennett, Department of Natural Resource Sciences and McGill School of Environment, McGill University, Ste. Anne de Bellevue, QC, Canada and Graham K. MacDonald, Institute on the Environment, University of Minnesota, St Paul, MN
Background/Question/Methods Agriculture covers approximately one third of the world’s land surface and is the largest contributor to human perturbations of global nitrogen and phosphorus (P) cycles. Recent trends of globalization, shifting human diets, and the industrialization of livestock productions systems have the potential to further exacerbate agriculture’s effect on biogeochemical cycles. We estimated the P flows through livestock production systems in Brazil, China, France, India, Kenya, Mexico, and the U.S.A. over the past 50 years to examine how trade and shifting human diets are influencing the global P cycle. We utilized historical data from the Food and Agriculture Organization to calculate the quantity of P in fertilizer applied to feed crops, feed crops, live animals, and processed livestock products. We included all major commodity feed crops, including cereals, tubers, pulses and oilseeds. Livestock products included were meat, milk and eggs. We utilized regional estimates of livestock diet composition and manure production rates to calculate P in manure produced and manure available for recycling to arable crops.
Results/Conclusions
Current average P fertilizer use efficiency (P harvested/P applied) for commodity feed crops ranged from 60% for China to 160% for Kenya, indicating the potential for pollution of surface waters on one end of the range and soil mining at the other end. The total quantity of P fertilizer applied to commodity feed crops, however, was on average only 18% and 39% of the total quantity of P flowing annually through livestock across all countries in 1961 and 2003, respectively, due to high inputs of P from forages, pastures, and rangelands. The P fertilizer use for feed crops relative to P from grazing increased for almost all countries due to shifts to more concentrated production systems and increased consumption of pork and poultry products. In addition, the percent of feed crops traded internationally more than doubled over this same time period. As crop and livestock production have intensified and become physically separated by increasing distances, P fertilizer use for feed crops relative to food crops has increased and the potential for recycling manure P back to crop lands has decreased. These historical trends provide important context from which to predict future P fertilizer demands and to identify policy options for sustainable resource management.
