Opinion: A "more ammonium solution" to mitigate nitrogen pollution and boost crop yields.

Two of the world’s great agricultural challenges require bold new approaches and could share a solution. Nitrogen (N) pollution, affecting water, air, and the climate, presents one massive challenge. Ninety percent of increased reactive N originates as synthetic fertilizer applied to agricultural fields or N fixed in them (1). Because crops take up only 42 to 47% of the total applied N, more than half is lost to the environment in some way (2, 3). Despite some recent regional improvements in nitrogen use efficiency (NUE), global average NUE has not increased since 1980. Yet even if by 2050 the world increased NUE by 50% (to ∼70%), likely 50% increases in food production would maintain N losses to the environment at roughly their present, unacceptable levels (3).\n\n\n\nWe can address pollution and boost crop yields by exploiting new tools that keep a higher share of soil nitrogen as ammonium while selecting and breeding crops to exploit an ammonium/nitrate balance. Nitrification-inhibiting traits originally discovered in some tropical grasses can be enhanced in cereal crops too. Image credit: Flickr/CIAT.\n\n\n\nA second challenge is to increase crop yields at a more rapid (linear) rate in coming decades to meet rising food demands without clearing more forests and releasing their carbon (3). Just as yield growth has historically resulted from synergies of crop breeding and management changes, future gains must rely on doing both in even smarter ways. Large yield growth by adding fertilizer or doubling irrigation is no longer possible or environmentally acceptable in most of the world (3⇓–5).\n\nThe scope of these challenges requires multiple new approaches, and here we make the case for a “more ammonium solution.” With the exception of paddy rice, nitrate dominates the inorganic N in modern agricultural soils, leading to most N … \n\n[↵][1]1To whom correspondence may be addressed. Email: tsearchi{at}princeton.edu or subbarao{at}jircas.affrc.go.jp.\n\n [1]: #xref-corresp-1-1