A Research Road Map for Responsible Use of Agricultural Nitrogen

Abstract

Nitrogen (N) is an essential but generally limiting nutrient for biological systems. Development of the Haber-Bosch industrial process for ammonia synthesis helped to relieve N limitation of agricultural production, fueling the Green Revolution and reducing hunger. However, the massive use of industrial N fertilizer has doubled the N moving through the global N cycle with dramatic environmental consequences that threaten planetary health. Thus, there is an urgent need to reduce losses of reactive N from agriculture, while ensuring sufficient N inputs for food security. Here we review current knowledge related to N use efficiency (NUE) in agriculture and identify research opportunities in the areas of agronomy, plant breeding, biological N fixation (BNF), soil N cycling, and modeling to achieve responsible, sustainable use of N in agriculture. Amongst these opportunities, improved agricultural practices that synchronize crop N demand with soil N availability are low-hanging fruit. Crop breeding that targets root and shoot physiological processes will likely increase N uptake and utilization of soil N, while breeding for BNF effectiveness in legumes will enhance overall system NUE. Likewise, engineering of novel N-fixing symbioses in non-legumes could reduce the need for chemical fertilizers in agroecosystems but is a much longer-term goal. The use of simulation modeling to conceptualize the complex, interwoven processes that affect agroecosystem NUE, along with multi-objective optimization, will also accelerate NUE gains.

Climate Change and Management Impacts on Soybean N Fixation, Soil N Mineralization, N2O Emissions, and Seed Yield

“…The increasing N mineralization and topsoil nitrate ( Figures 4 – 6 ) with the simultaneous decrease in seed N uptake and soybean yields under climate change are of concern. Actions should be taken to manage the unused N after crop harvest, such as using cover crops ( Udvardi et al, 2021 ). Our results revealed a 19% average increase in N 2 O with climate change, which is probably an underestimate because we initialized the model at the start of every year.…”

Can We Harness “Enviromics” to Accelerate Crop Improvement by Integrating Breeding and Agronomy?

“…Successful applications have been demonstrated for commercial maize breeding in the US corn-belt (Cooper et al, 2014a;Gaffney et al, 2015). Opportunities are emerging for development of integrated breeding-agronomy approaches for other crops and target regions to tackle current GxExM challenges and the anticipated impacts of climate change (Hatfield and Walthall, 2015;Hammer et al, 2019;Beres et al, 2020;de los Campos et al, 2020;Messina et al, 2020;Ramirez-Villegas et al, 2020;Crossa et al, 2021;Hunt et al, 2021;Kusmec et al, 2021;Smith et al, 2021;Udvardi et al, 2021).…”

“…Such applications of enviromics to analyze GxExM interactions for yield are not restricted to water and drought. Alternative environmental descriptors, such as nitrogen availability (Bänziger et al, 1999;DeBruin et al, 2017;Mueller et al, 2019;Udvardi et al, 2021), can also be applied as appropriate for the crop breeding target, cropping system, and TPE.…”

Biological nitrogen fixation and prospects for ecological intensification in cereal-based cropping systems

“…In many regions, fertilizer costs are low, and their liberal or excessive use has led to distinct environmental and ecological degradation problems, including depletion of soil organic matter due to oxidation of soil C, surface and groundwater pollution, and increased emissions of greenhouse gases ( Peoples et al, 2004b , UNEP and WHRC, 2007 , Erismann et al, 2008 ). While synthetic N will undoubtedly remain essential for ensuring global food supply, and optimizing the efficiency of its use remains a key objective ( Crews and Peoples, 2005 , Ladha et al, 2005 , Ladha et al, 2020 ), it is clear that it is also desirable to explore strategies to increase inputs from alternative sources of N with lower environmental costs – such as BNF – to provide opportunities to reduce agriculture’s high reliance upon fertilizer N ( Jensen et al, 2012 , Ladha et al, 2016 , Peoples et al, 2019 , Udvardi et al, 2021 ).…”