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. 2020 Aug 10;150(2):139–180. doi: 10.1007/s10533-020-00691-6

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© The Author(s) 2020

Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 3 — Change in nitrogen and phosphorus fertilizer use in the US over time as a total nitrogen, b anhydrous NH₄ and NH₄–NO_3, c mixed N solutions (urea-NH₄–NO₃ and urea), d total phosphorus (as P), e superphosphates, and f combined N-phosphorus solutions. Data are from https://www.ers.usda.gov/data-products/fertilizer-use-and-price. Trend lines are shown to highlight specific relationships described in text. Icons are from the UMCES-IAN image library