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  • 1
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    Spatially explicit estimates of N2O emissions from croplands suggest climate mitigation opportunities from improved fertilizer management (2016)
    Wiley
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    Publication Date: 2016-05-18
    Description: With increasing nitrogen (N) application to croplands required to support growing food demand, mitigating N 2 O emissions from agricultural soils is a global challenge. National greenhouse gas emissions accounting typically estimates N 2 O emissions at the country scale by aggregating all crops, under the assumption that N 2 O emissions are linearly related to N application. However, field studies and meta-analyses indicate a nonlinear relationship, in which N 2 O emissions are relatively greater at higher N application rates. Here we apply a super-linear emissions response model to crop-specific, spatially-explicit synthetic N fertilizer and manure N inputs to provide subnational accounting of global N 2 O emissions from croplands. We estimate 0.66 Tg of N 2 O-N direct global emissions circa 2000, with 50% of emissions concentrated in 13% of harvested area. Compared to estimates from the IPCC Tier 1 linear model, our updated N 2 O emissions range from 20-40% lower throughout Sub-Saharan Africa and Eastern Europe, to 〉120% greater in some Western European countries. At low N application rates, the weak non-linear response of N 2 O emissions suggests that relatively large increases in N fertilizer application would generate relatively small increases in N 2 O emissions. Since aggregated fertilizer data generate underestimation bias in nonlinear models, high-resolution N application data are critical to support accurate N 2 O emissions estimates. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
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  • 2
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    Quantifying the limitation to world cereal production due to soil phosphorus status (2018)
    Wiley
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    Publication Date: 2018-01-09
    Description: Phosphorus (P) is an essential element for plant growth. Low P availability in soils is likely to limit crop yields in many parts of the world, but this effect has never been quantified at the global scale by process-based models. Here we attempt to estimate P limitation in 3 major cereals worldwide for the year 2000 by combining information on soil P distribution in croplands and a generic crop model, while accounting for the nature of soil-plant P transport. As a global average, the diffusion limited soil P supply meets the crop's P demand corresponding to the climatic yield potential, due to the legacy soil P in highly fertilized areas. However, when focusing on the spatial distribution of P supply vs. demand, we found strong limitation in regions like North and South America, Africa and Eastern Europe. Averaged over grid-cells where P supply is lower than demand, the global yield gap due to soil P is estimated at 22, 55 and 26 % in winter wheat, maize and rice. Assuming that a fraction (20%) of the annual P applied in fertilizers is directly available to the plant, the global P yield gap lowers by only 5 – 10 % underlying the importance of the existing soil P supply in sustaining crop yields. The study offers a base for exploring P limitation in crops worldwide, but with certain limitations remaining. These could be better accounted for by describing the agricultural P cycle with a fully coupled and mechanistic soil-crop model.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Declining spatial efficiency of global cropland nitrogen allocation (2017)
    Wiley
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    Publication Date: 2017-01-14
    Description: 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 tradeoff 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 tradeoff frontiers. Improvements in agronomic technology have substantially increased cropping system yield potentials and expanded N-driven crop production possibilities. However, we find 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.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Plant uptake and stream chemistry set global bounds on nitrogen gas emissions from humid tropical forests (2017)
    Wiley
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    Publication Date: 2017-03-01
    Description: Denitrification and hydrologic leaching are the two major pathways by which nitrogen is lost from the terrestrial biosphere. Humid tropical forests are thought to dominate denitrification from unmanaged lands globally, but there is large uncertainty about the range and key drivers of total N gas emissions across the biome. We combined pantropical measures of small watershed stream chemistry with ecosystem modeling to determine total nitrogen gas losses and associated uncertainty across humid tropical forests. Our calculations reveal that denitrification in soils and along hydrologic flowpaths contributes on average 〉45% of total watershed N losses. However, when denitrification occurs exclusively in shallow soils, simulations indicate that gas emissions would exceed N inputs and render plants severely N-limited, which contradicts observations of widespread N-sufficiency in tropical forests. Our analyses suggest an upper bound on soil denitrification of ~80% of total external N losses beyond which tropical plant growth would be compromised.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Evaluating the drought response of CMIP5 models using global gross primary productivity, leaf area, precipitation and soil moisture data (2016)
    Wiley
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    Publication Date: 2016-12-09
    Description: Realistic representation of vegetation's response to drought is important for understanding terrestrial carbon cycling. We evaluated 9 Earth System Models from the historical experiment of the Coupled Model Intercomparison Project Phase 5 (CMIP5) for the response of gross primary productivity (GPP) and leaf area index (LAI) to hydrological anomalies. Hydrological anomalies were characterized by the standardized precipitation index (SPI) and surface soil moisture anomalies (SMA). GPP and LAI in models were on average more responsive to SPI than in observations revealed through several indicators. First, we find higher mean correlations between global annual anomalies of GPP and SPI in models than observations. Second, the maximum correlation between GPP and SPI across 1-24 month timescales is higher in models than observations. And finally we found stronger excursions of GPP to extreme dry or wet events. Similar to GPP, LAI responded more to SPI in models than observations. The over-response of models is smaller if evaluated based on SMA instead of SPI. LAI responses to SMA are inconsistent among models, showing both higher and lower LAI when soil moisture is reduced. The timescale of maximum correlation is shorter in models than the observation for GPP and the markedly different response timescales among models for LAI indicate gaps in understanding how variability of water availability affects foliar cover. The discrepancy of responses derived from SPI and SMA among models, and between models and observations calls for improvement in understanding the dynamics of plant-available water in addition to how vegetation responds to these anomalies.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Reducing emissions from agriculture to meet the 2°C target (2016)
    Wiley
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    Publication Date: 2016-05-18
    Description: More than 100 countries pledged to reduce agricultural greenhouse gas (GHG) emissions (Richards et al ., 2015a) in the 2015 Paris Agreement of the United Nations Framework Convention on Climate Change. Yet technical information about how much mitigation is needed in the sector versus how much is feasible remains poor. We identify a preliminary global target for reducing emissions from agriculture of ~1 GtCO 2 e/yr by 2030 to limit warming in 2100 to 2°C above pre-industrial levels. Yet plausible agricultural development pathways with mitigation co-benefits deliver only 21 to 40% of needed mitigation. The target indicates that more transformative technical and policy options will be needed, such as methane inhibitors and finance for new practices. A more comprehensive target for the 2°C limit should be developed to include soil carbon and agriculture-related mitigation options. Excluding agricultural emissions from mitigation targets and plans will increase the cost of mitigation in other sectors or reduce the feasibility of meeting the 2°C limit. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
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