Declining spatial efficiency of global cropland nitrogen allocation. Issue 2 (3rd February 2017)

• Record Type: Journal Article
• Authors: Mueller, Nathaniel D.; Lassaletta, Luis; Runck, Bryan C.; Billen, Gilles; Garnier, Josette; Gerber, James S.
• Is Part Of: Global biogeochemical cycles. Volume 31:Issue 2(2017:Feb.)
• Page Start: 245
• Page End: 257
• Publication Date: 2017-02-03
• Subjects: global cropland -- nitrogen use efficiency -- nitrogen allocation -- environmental nitrogen losses; Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1002/2016GB005515
• Languages: English
• ISSNs: 0886-6236

Abstract

Abstract: Efficiently allocating nitrogen (N) across space maximizes crop productivity for a given amount of N input and reduces N losses to the environment. Here we quantify changes in the global spatial efficiency of cropland N use by calculating historical trade‐off frontiers relating N inputs to possible N yield assuming efficient allocation. Time series cropland N budgets from 1961 to 2009 characterize the evolution of N input‐yield response functions across 12 regions and are the basis for constructing trade‐off frontiers. Improvements in agronomic technology have substantially increased cropping system yield potentials and expanded N‐driven crop production possibilities. However, we find that these gains are compromised by the declining spatial efficiency of N use across regions. Since the start of the Green Revolution, N inputs and yields have moved farther from the optimal frontier over time; in recent years (1994–2009), global N surplus has grown to a value that is 69% greater than what is possible with efficient N allocation between regions. To reflect regional pollution and agricultural development goals, we construct scenarios that restrict reallocation, finding that these changes only slightly decrease potential gains in nitrogen use efficiency. Our results are inherently conservative due to the regional unit of analysis, meaning a larger potential exists than is quantified here for cross‐scale policies to promote spatially efficient N use. Key Points: Spatially efficient use of N maximizes crop productivity for a given amount of N input and decreases N losses to the environment Global patterns of N use have become less spatially efficient since the 1960s Contemporary N surplus is 69% greater than would be produced under spatially efficient allocation of N inputs