Nutrient Imbalances: Follow the Waste

Abstract

In their Policy Forum (“Nutrient imbalances in agricultural development,” 19 June, p. [1519][1]), P. M. Vitousek and colleagues appropriately addressed the consequences of both overextraction and excess application of nutrients in low-input, rotation, and high-input corn production systems in Kenya, the United States, and China, respectively. The authors provided several on-farm mitigating approaches to these imbalances and called for a more sustainable approach to nutrient management in both developed and developing nations. Unfortunately, the human waste stream and the resulting nutrient redistribution went unmentioned. Over the past 200 years, global populations have become increasingly urban, shifting from 97% rural in 1800 to about 50% in 2007 (75% in developed countries) ([ 1 ][2]). Nutrients in plant and animal products collected broadly across rural landscapes are increasingly concentrated in urban environs where waste removal efforts result in transformation of nutrients into gases, dilution into rivers and marine bodies, and deposition in pits and landfills. Only a fraction of these assets (nutrients and carbon) are ever returned to rural lands. As a result, soils are slowly being drained of trace elements, soil carbon reserves are being depleted, and it is necessary to mine nutrients and chemically produce N fertilizer to satisfy crop demands. Global N fertilizer use ([ 2 ][3]) currently outpaces global human N demand ([ 1 ][2], [ 3 ][4]) by a factor of 7 at an annual energy expense equivalent to 1.1 billion barrels of oil. Conversely, N in human excreta in urban centers is nearly equivalent to the total global anhydrous NH3-N production and represents sufficient N to fertilize 100 million hectares of cropland at 150 kg N ha−1 year−1. Sustainable agriculture cannot be achieved until we learn to efficiently and safely redistribute the nutrients in agricultural byproducts and human excreta to the soils of rural landscapes. 1. [↵][5] United Nations, “World urbanization prospects: The 2007 revision—Highlights” (United Nations, Tech. Rep. no. E.04.XIII.6, 2008). 2. [↵][6] 1. J. N. Galloway 2. et al ., Science 320, 889 (2008). [OpenUrl][7][Abstract/FREE Full Text][8] 3. [↵][9] 1. D. H. Calloway, 2. S. Margen , J. Nutr. 101, 205 (1971). [OpenUrl][10][Abstract/FREE Full Text][11] [1]: /lookup/doi/10.1126/science.1170261 [2]: #ref-1 [3]: #ref-2 [4]: #ref-3 [5]: #xref-ref-1-1 View reference 1 in text [6]: #xref-ref-2-1 View reference 2 in text [7]: {openurl}?query=rft.jtitle%253DScience%26rft.stitle%253DScience%26rft.issn%253D0036-8075%26rft.aulast%253DGalloway%26rft.auinit1%253DJ.%2BN.%26rft.volume%253D320%26rft.issue%253D5878%26rft.spage%253D889%26rft.epage%253D892%26rft.atitle%253DTransformation%2Bof%2Bthe%2BNitrogen%2BCycle%253A%2BRecent%2BTrends%252C%2BQuestions%252C%2Band%2BPotential%2BSolutions%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.1136674%26rft_id%253Dinfo%253Apmid%252F18487183%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 [8]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic2NpIjtzOjU6InJlc2lkIjtzOjEyOiIzMjAvNTg3OC84ODkiO3M6NDoiYXRvbSI7czoyNDoiL3NjaS8zMjYvNTk1My82NjUuMS5hdG9tIjt9czo4OiJmcmFnbWVudCI7czowOiIiO30= [9]: #xref-ref-3-1 View reference 3 in text [10]: {openurl}?query=rft.jtitle%253DJournal%2Bof%2BNutrition%26rft.stitle%253DJ.%2BNutr.%26rft.issn%253D0022-3166%26rft.aulast%253DCalloway%26rft.auinit1%253DD.%2BH.%26rft.volume%253D101%26rft.issue%253D2%26rft.spage%253D205%26rft.epage%253D216%26rft.atitle%253DVariation%2Bin%2BEndogenous%2BNitrogen%2BExcretion%2Band%2BDietary%2BNitrogen%2BUtilization%2Bas%2BDeterminants%2Bof%2BHuman%2BProtein%2BRequirement%26rft_id%253Dinfo%253Apmid%252F5540441%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 [11]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6OToibnV0cml0aW9uIjtzOjU6InJlc2lkIjtzOjk6IjEwMS8yLzIwNSI7czo0OiJhdG9tIjtzOjI0OiIvc2NpLzMyNi81OTUzLzY2NS4xLmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ==