Nitrogen fertilization challenges the climate benefit of cellulosic biofuels

Ruan, Leilei; Bhardwaj, Ajay Kumar; Hamilton, Stephen K.; Robertson, G. Philip

doi:10.1088/1748-9326/11/6/064007

Cited by 80 publications

(76 citation statements)

References 40 publications

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“…When comparing AONRs among crops in 2013, a lack of overlap of the 95% CIs of the AONRs suggests that switchgrass required more N fertilizer to reach maximum biomass yield compared to TLI-C2 for grain yield at spring seeded locations. Increasing levels of N fertilization of switchgrass resulted in an exponential increase in N 2 O emissions, which can negate the climate change mitigation benefits of this bioenergy crop (Ruan et al, 2016). Additionally, reduced N fertilizer requirements for TLI-C2 offers economic incentives for adoption of this perennial crop.…”

Section: Agronomic Optimum Nitrogen Ratesmentioning

confidence: 99%

“…Water quality could be improved as fertilized perennial crops leach less nitrate than annuals (McIsaac et al, 2010). Reducing N fertilization reduces greenhouse gas emissions related to N fertilizer volatilization (Ruan et al, 2016). Carbon sequestration occurs below perennials as root C is transferred via exudates and turnover to soil organic matter at depths where it is protected from decomposition (Tiemann and Grandy, 2015).…”

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confidence: 99%

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Intermediate Wheatgrass Grain and Forage Yield Responses to Nitrogen Fertilization

et al. 2017

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Perennial crops have fewer environmental impacts compared to annual crops, but there are no perennial grains available to replace the annual grains that occupy a majority of U.S. cropland. Here we report grain and biomass yields from an improved breeding population of intermediate wheatgrass (IWG) [Th inopyrum intermedium (Host) Buckworth & Dewey], a perennial grass being domesticated to serve as the fi rst widely grown perennial grain crop. Our objective was to measure grain and biomass yields of this improved grain-type IWG (TLI-C2), a forage variety of IWG (cultivar Rush), and switchgrass (Panicum virgatum L.) in response to N fertilization rates ranging from 0 to 200 kg N ha -1 . TLI-C2 grain yields responded quadratically to increasing N rates in all but one environment, but yields declined at high N rates due to lodging. TLI-C2 grain yields were highest during the fi rst year of fertilization, yielding 961 and 893 kg ha -1 when fertilized at agronomically optimum nitrogen rates (AONRs) of 61 and 96 kg N ha -1 for stands seeded in fall of 2011 and spring of 2012, respectively. Grain yields declined with stand age. When fertilized with AONRs for grain, biomass yields of TLI-C2 harvested aft er grain ranged from 9.2 to 12.3 Mg ha -1 and had similar forage and bioenergy quality characteristics compared to Rush, which demonstrates the potential to manage TLI-C2 as a dual-use cropping system for both grain and forage.

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Section: Agronomic Optimum Nitrogen Ratesmentioning

confidence: 99%

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confidence: 99%

Intermediate Wheatgrass Grain and Forage Yield Responses to Nitrogen Fertilization

et al. 2017

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“…Conversely, increased N 2 O emissions from N fertilizer were largely compensated for by increased yields in injected scenarios and, to a lesser extent, in broadcast ammonium nitrate scenarios. These results contrast with recent assertions that increased N application rate compromises the GHG mitigation benefits of cellulosic fuels (Ruan et al ., ). Although GHGs increased with N in broadcast urea scenarios, they were minimally affected by N application rate in broadcast ammonium nitrate scenarios and tended to decline slightly with increasing N application rate in injected scenarios, at least when expressed on an energy yield basis.…”

Section: Discussionmentioning

confidence: 97%

Trade‐offs across productivity, GHG intensity, and pollutant loads from second‐generation sorghum bioenergy

et al. 2017

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Greenhouse gas (GHG) intensity is frequently used to assess the mitigation potential of biofuels; however, failure to quantify other environmental impacts may result in unintended consequences, effectively shifting the environmental burden of fuel production rather than reducing it. We modeled production of E 85 , a gasoline/ethanol blend, from forage sorghum (Sorghum bicolor cv. photoperiod LS) grown, processed, and consumed in California's Imperial Valley in order to evaluate the influence of nitrogen (N) management on well-to-wheel (WTW) environmental impacts from cellulosic ethanol. We simulated 25 N management scenarios varying application rate, application method, and N source. Life cycle environmental impacts were characterized using the EPA's criteria for emissions affecting the environment and human health. Our results suggest efficient use of N is an important pathway for minimizing WTW emissions on an energy yield basis. Simulations in which N was injected had the highest nitrogen use efficiency. Even at rates as high as 450 kg N ha À1 , injected N simulations generated a yield response sufficient to outweigh accompanying increases in most N-induced emissions on an energy yield basis. Thus, within the biofuel life cycle, trade-offs across productivity, GHG intensity, and pollutant loads may be possible to avoid at regional to global scales. However, trade-offs were seemingly unavoidable when impacts from E 85 were compared to those of conventional gasoline. The GHG intensity of sorghum-derived E 85 ranged from 29 to 44 g CO 2 eq MJ À1 , roughly 1/3 to 1/2 that of gasoline. Conversely, emissions contributing to local air and water pollution tended to be substantially higher in the E 85 life cycle. These adverse impacts were strongly influenced by N management and could be partially mitigated by efficient application of N fertilizers. Together, our results emphasize the importance of minimizing on-farm emissions in maximizing both the environmental benefits and profitability of biofuels.

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“…Methane fluxes reported in the literature from switchgrass production range from -3.8 to 2.4 g CH 4 -C ha -1 d -1 for fertilized monoculture switchgrass and −6.8 to -3.8 g CH 4 -C ha -1 d -1 for unfertilized switchgrass and are predominately sinks for CH 4 -C (Nikiema et al, 2011;Schmer et al, 2012;Wile et al, 2014;Raun et al, 2016). Total growing season soil CH 4 -C uptake was not significantly different among the PM, IC and SM treatments (Table 4).…”

Section: Ch 4 -C Flux Rates and Seasonal Emissionsmentioning

confidence: 99%

“…Schmer et al (2012) found N 2 O-N fluxes ranged from 0.24 to 8.6 g N 2 O-N ha -1 d -1 for fertilized switchgrass. Raun et al (2016) in a …”

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Intercropping with Switchgrass Improves Net Greenhouse Gas Balance in Hybrid Poplar Plantations on a Sand Soil

Collins

Fay

Kimura³

et al. 2017

Soil Science Society of America Journal

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In the Pacific Northwest, commercial hybrid poplar (Populus generosa Henry × Populus canadensis Moench.) is managed at low stocking densities under irrigation for high-value timber production. The objectives of this study were to measure greenhouse gas emissions (CH4, CO 2 , and N 2 O) during intercropping of switchgrass (Panicum virgatum L.) with hybrid poplar; estimate losses of fertilizer-N as N 2 O, and estimate global warming potentials (GWP) of the intercrop. Cumulative above-ground biomass-C of the poplar monoculture (PM) closely matched the four year growing season (GS) soil CO 2 -C emissions, where aboveground biomass of the switchgrass monoculture (SM) and intercrop (IC) exceeded GS CO 2 -C emissions by 14.1 Mg C ha -1 . Soil CH 4 -C uptake was not significantly different between treatments, while GS N 2 O-N emissions for PM were ~80% lower than both IC and SM. N 2 O emissions factors averaged 0.7% of the applied N-fertilizer. Cumulative contributions of CO 2 emissions to GWP were offset by biomass-C resulting in a near zero balance (−5.1 Mg CO 2eq ha -1 ) for the PM, where, IC and SM sequestered significantly more CO 2 resulting in a net GWP of −42.5 and -32.2 Mg CO 2eq ha -1 , respectively. Intercropping with switchgrass can improve the net greenhouse gas balance of hybrid poplar. Continued research is needed on the effects of irrigated bioenergy production on GHG emissions in intercropped systems as they will become increasingly important as agricultural water use, water availability and quality are challenged by climate change.Abbreviations: DM, dry matter; GHG, greenhouse gas; GS, growing season; GWP, global warming potential; N EF , nitrogen emissions factor; PM, monoculture poplar; IC, poplar/ switchgrass intercrop; SM, switchgrass monoculture M ajor shifts in crop production will occur as farmers prepare to supply the demand for biomass feedstocks for production of renewable biofuels. These shifts will affect agroecosystem services related to water use, carbon storage, nutrient cycling and greenhouse gas (GHG) emissions that have direct effects on air, water, and soil quality (Popp et al., 2014). Perennial grasses are an important source of feed and fiber and are considered sustainable bioenergy crops because they have the capacity to produce large quantities of biomass, can be grown on marginal lands, improve soil quality and protect soils from erosion (Lemus and Lal, 2005;Sartori et al., 2006; Casler et al., 2009;Gelfand et al., 2013). Switchgrass (Panicum virgatum L.) is a prominent biomass crop for the US biofuel industry (Sanderson et al., 2007; Casler et al., 2009) because it yields well on a variety of soil types, is drought-tolerant, and has low fertility requirements (McLaughlin and Kszos, 2005;Lemus and Lal, 2005;Kimura et al., 2015). The root system of switchgrass has been shown to offset C losses and promotes C sequestration by adding a Core Ideas• A critical issue in the production of biofuels has been the competition with food crops• Intercropping switchgrass and hybrid poplar wa...

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Nitrogen fertilization challenges the climate benefit of cellulosic biofuels

Cited by 80 publications

References 40 publications

Intermediate Wheatgrass Grain and Forage Yield Responses to Nitrogen Fertilization

Intermediate Wheatgrass Grain and Forage Yield Responses to Nitrogen Fertilization

Trade‐offs across productivity, GHG intensity, and pollutant loads from second‐generation sorghum bioenergy

Intercropping with Switchgrass Improves Net Greenhouse Gas Balance in Hybrid Poplar Plantations on a Sand Soil

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