The nitrogen footprint of organic food in the United States

We estimated the reactive nitrogen (Nr) lost per unit food Nr consumed for organic food production in the United States and compared it to conventional production. We used a nitrogen footprint model approach, which accounts for both differences in Nr losses as well as differences in productivity of the two systems. Additionally, we quantified the types of Nr inputs (new versus recycled) that are used in both production systems. We estimated Nr losses from organic crop and animal production to be of comparable magnitude to conventional production losses, with the exception of beef. While Nr losses from organic vegetables are possibly higher (+37%), Nr losses from organic grains, starchy roots, legumes are likely of similar magnitude to conventional production (+7%, +6%, −12%, respectively). Nr losses from organic poultry, pigmeat, and dairy production are also likely comparable to conventional production (+9%, +10%, +12%, respectively), while Nr losses from organic beef production were estimated to be higher (+124%). Due to the high variability and high uncertainty in Nr efficiency in both systems we cannot make conclusions yet on the statistical significance of these potential differences. Conventional production relies heavily on the creation of new Nr (70%–90% of inputs are from new Nr sources like synthetic fertilizer), whereas organic production primarily utilizes already existing Nr (0%–50% of organic inputs are from new Nr sources like leguminous N fixation). Consuming organically produced foods has little impact on an individual's food N footprint but changes the percentage of new versus recycled Nr in the footprint. With the exception of beef, Nr losses from organic production per unit N in product are comparable to conventional production. However, organic production requires the creation of less new Nr, which could reduce global Nr pollution. (letter)