Response—Nutrient Imbalances

As DeLuca suggests, applications of N fertilizer worldwide exceed human consumption of that N in the form of protein by several-fold. Our Policy Forum focused in part on the more than 80% of fertilizer N (and P) that does not make it into our diet—the fertilizer that could in some sense be considered “wasted.” DeLuca is correct in pointing out that closing nutrient cycles by returning agriculturally derived nutrients to crops would make an additional contribution to the sustainability of intensive agriculture. A parallel problem exists for nutrients in animal waste, due to the adoption of confined animal feeding operations (CAFO), which use feed derived from fertilized crops in distant areas ([ 1 ][1], [ 2 ][2]). In either case, the result is too much N and P in waste near the city or CAFO, and not enough where food or feed is grown. Albiac points out, and our Policy Forum noted, that the reduction in excess nutrient applications in the midwestern United States and Northern Europe has not ended serious nutrient pollution of surface or groundwater (or the atmosphere) in those regions. Part of the problem may be the decades-long residence time (from application to appearance in surface water) of added nutrients in many systems ([ 3 ][3]); part no doubt reflects inadequacies of the policy instruments designed to reduce water (and air) pollution by excess agricultural nutrients. The European Union in particular has put substantial resources into efforts to reduce this pollution, as Albiac describes, and the relatively small successes to date are disappointing. Albiac points to restricted spatial coverage and inadequate engagement of stakeholders as reasons for failed nutrient policies. Equally important, efforts to date have not been sufficiently systematic; they have not considered the full mass balance of excess nutrients and their multiple possible fates. Excess nutrients cannot be controlled piecemeal (for example, by considering only nitrate rather than total N or by considering effects on aquatic systems in isolation from effects on the atmosphere). Successful policies must address the problem of excessive nutrient applications at their source. Maintaining the high levels of production that we require to meet aggregate cereal and meat demand while reducing losses of nutrients to the environment represents a very difficult challenge. Meeting that challenge will require careful, well-monitored, long-term experiments with policy instruments as well as with agricultural nutrients themselves. 1. [↵][4] 1. R. Naylor 2. et al ., Science 310, 1621 (2005). [OpenUrl][5][Abstract/FREE Full Text][6] 2. [↵][7] 1. G. P. Robertson, 2. P. M. Vitousek , Ann. Rev. Environ. Res. 34, 97 (2009). [OpenUrl][8][CrossRef][9] 3. [↵][10] 1. V. Escaravage, 2. P. M. J. Herman, 3. C. H. R. Heip , J. Integr. Environ. Sci. 3, 97 (2006). [OpenUrl][11][CrossRef][12] [1]: #ref-1 [2]: #ref-2 [3]: #ref-3 [4]: #xref-ref-1-1 View reference 1 in text [5]: {openurl}?query=rft.jtitle%253DScience%26rft.stitle%253DScience%26rft.issn%253D0036-8075%26rft.aulast%253DNaylor%26rft.auinit1%253DR.%26rft.volume%253D310%26rft.issue%253D5754%26rft.spage%253D1621%26rft.epage%253D1622%26rft.atitle%253DAGRICULTURE%253A%2BLosing%2Bthe%2BLinks%2BBetween%2BLivestock%2Band%2BLand%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.1117856%26rft_id%253Dinfo%253Apmid%252F16339432%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [6]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic2NpIjtzOjU6InJlc2lkIjtzOjEzOiIzMTAvNTc1NC8xNjIxIjtzOjQ6ImF0b20iO3M6MjQ6Ii9zY2kvMzI2LzU5NTMvNjY1LjMuYXRvbSI7fXM6ODoiZnJhZ21lbnQiO3M6MDoiIjt9 [7]: #xref-ref-2-1 View reference 2 in text [8]: {openurl}?query=rft_id%253Dinfo%253Adoi%252F10.1146%252Fannurev.environ.032108.105046%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [9]: /lookup/external-ref?access_num=10.1146/annurev.environ.032108.105046&link_type=DOI [10]: #xref-ref-3-1 View reference 3 in text [11]: {openurl}?query=rft_id%253Dinfo%253Adoi%252F10.1080%252F15693430600659113%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [12]: /lookup/external-ref?access_num=10.1080/15693430600659113&link_type=DOI