Relationships of Nitrous Oxide Emissions to Fertilizer Nitrogen Recovery Efficiencies in Rain-fed and Irrigated Corn Production Systems: Data Review

Justification:
Nitrous oxide (N2O) emissions from corn production systems are a large societal concern because so much of the N fertilizer applied to crop production in the United States is applied to corn, and because agriculture alone accounts for the majority of N2O emissions from all sources. The IPCC (2006) has estimated that an average of approximately 1.0% of the N fertilizer applied is lost as N2O, but we know from our own studies in rain-fed corn production that estimated emissions can sometimes exceed the equivalent of 5% of the N in the N fertilizers applied (e.g. Omonode et al., 2010).

Over the years of scientific monitoring of N2O emissions, the predominant reporting method has been to quantify episodic and/or cumulative growing season N2O emissions per unit land area. Later refereed publications included acknowledgement of the importance of reporting yieldscaled N2O emissions, but not until relatively recently has there been a plea to focus on emissions within the context of actual N use efficiencies (e.g. Snyder et al., 2014). The recent meta-analysis by Decock (2014) highlighted the low proportion of past N2O emission studies that included critical information on treatment effects on crop N export (let alone any mention of crop N uptake).

Unfortunately, very few greenhouse gas researchers in field crop systems have measured more than grain yield in their evaluations of crop response to N management. While grain yield responses to N fertilizer –especially in experiments were a zero N rate is included – permit calculation of an overall N use efficiency (NUE), they don’t account for the actual N uptake by plants. Determination of whole-plant biomass at maturity followed by grinding and plant-component N concentration measurements are the only pathway to calculating the overall gain in whole-plant N uptake (NU) for a particular N management system comprising a specific N source, N rate (versus a zero N control), N timing, and N placement combination. The difference in whole plant N at harvest is characterized, relative to the control N treatment, as N recovery efficiency (NRE). The ultimate N efficiency parameter, therefore, that means the most to understanding the production system context of fertilizer N fate and associated N2O emissions is NRE and not simply NUE alone.

The central hypothesis of this proposal is that increased corn plant N uptake (as a fraction of the fertilizer N applied) will be associated with reduced N2O emissions on area-scaled, yield-scaled, and NRE-scaled (i.e. plant N uptake per unit of N fertilizer initially applied) methods of interpreting relative N2O emissions from different management systems for corn production.

Fertilizer industry associations such as IPNI and TFI have been strong proponents of the 4R’s (source, rate time and place) with respect to N management for many years. Further advances in promotion of sustainable nutrient practices are being discussed with other industry and university partners associated with the Field to Market efforts. Both TFI and IPNI are committed to updating the Field to Market’s “Fieldprint Calculator” for nitrous oxide estimation to version 3.0 by June of 2016. Sufficient documentation and synthesis of the existing knowledge of corn NRE and NUE relative to cumulative N2O emissions needs to be accomplished first. The strength of the Colorado (USDA-ARS) and Purdue research on N2O emissions research programs is that they have looked at numerous N management variables (source, rate, timing and placement) while also gathering whole-plant N accumulations at maturity. This distinguishes this work from that of many others in that most N2O emission experiments did not measure whole-plant N uptake. Another strength of the Colorado and Purdue work is that they have worked extensively with common N placement and N timing approaches as well as with N sources both with and without nitrification or urease inhibitors. The literature from Colorado and Purdue that described the NUE and NRE gains in conjunction with N management system impacts on N2O emissions is only partially completed. Both Dr. Halvorson and Purdue has a data base on past field experiments where corn whole-plant N was measured but not reported yet. There may be other such plant N uptake sources in North American, and we will ask other authors of N2O emission studies.

Because most of the relevant corn N uptake data gathered in conjunction with experiments that measured N2O emissions has never been reported, we propose to complete the first-ever review of this important relationship.

Objectives:

1. Relate cumulative growing-season nitrous oxide (N2O) emissions to existing data on corn whole-plant N uptake (NU) and apparent nitrogen recovery efficiencies (NRE) in previous N2O emissions research in North America involving changing N management treatments (whether focused on N source, N rate, N timing and/or N placement) in both irrigated and rainfed corn production systems.
2. To illustrate the relationships between corn N uptake (apparent N recovery) and N2O emissions in different production environments and at different corn yield levels.

Data Sources:

1. Dr. Halvorson has accumulated whole-plant corn N data from over 400 N management plots in his N2O emission experiments conducted in Colorado between 2002 and 2014. These N management treatment variables include factors include N source, N rate, N placement and N efficiency additives. Dr. Halvorson’s experiments always included a zero N rate, and that facilitates the relative NU measurements and interpretation of corn plant NRE from N fertilizer sources.
2. Dr. Vyn has accumulated whole-plant N data from over 300 N management plots in his N2O emission experiments conducted in Indiana between 2010 and 2014. These experiments have included management treatments comparing N rates/placement from both UAN-N and NH3-N sources, tillage systems, presence or absence of nitrification inhibitors, and alternate N application timings. Some of this data has already been reported in the literature (see papers by Omonode et al., 2015, by Burzaco et al., 2014).
3. Other literature: Some whole-plant corn N data has also been reported from N2O emission experiments conducted in Minnesota (principally in the work by R. Venterea and co-authors (e.g. in 2011), in other Purdue studies involving simultaneous N2O and nitrate-N losses to tile drains (Hernandez-Ramirez et al., 2014) and in Spain (Sanz Cobena et al., 2012). Whenever relevant literature is found, we will ask the authors for the plot-level N uptake data in order to conduct the most robust statistical analyses that we can muster on the relationships with cumulative N2O emissions.

Deliverables:

1. A 3-month progress report will be distributed to all funding partners in mid-September, 2015.
2. By November 20, 2015, we will have completed a synthesis-analysis review of the relationships between growing-season N2O emissions and corn yield, NU and NRE responses to various N fertilizer management treatment combinations (N sources, N rates, nitrification inhibitors and N efficiency additives, N timing, and N placement/tillage systems). In this review, we will rely extensively on the data assembled by Dr. Ardell Halvorson from 2001-2014 (primarily for irrigated corn in Colorado) and by Vyn and Omonode from 2010-2014 (for rain-fed corn in Indiana). However, we will also include other data assembled in North America (e.g. in Minnesota by Venterea et al. and in Indiana by Hernandez-Ramirez and Brouder).
3. By February 1, 2016 we will have submitted our review publication on the known relationships between N2O emissions and corn NU and NRE to an appropriate refereed journal.
4. All 3 investigators are expected to make oral and poster presentations to relevant science and industry sponsored meetings such as the Annual Meetings of the American Society of Agronomy, North-Central Extension-Industry Soil Fertility Conference, state-level CCA Conferences, and perhaps at a future 4R Nutrient Stewardship Summit (of course some of these events will depend on invitations by the respective program organizing committees).
5. By December 31, 2015, all data collected with this project’s funding will be placed in a designated data repository.

Partial List of Background References:
Burzaco, J.P., D.R. Smith, and T.J. Vyn. 2013. Nitrous oxide emissions in Midwest US maize production vary widely with band-injected N fertilizer rates, timing and nitrapyrin presence. Environ. Res. Lett. 8:1-11.
Burzaco, Juan P., Ignacio A. Ciampitti, and Tony J. Vyn. 2014. Nitrapyrin impacts on maize yield and nitrogen use efficiency with spring-applied nitrogen: Field Studies vs. Meta-Analysis Comparison. Agron. J. 106:753–760; doi:10.2134/agronj2013.0043.
Decock, C. 2014. Mitigatin nitrous oxide emissions from corn cropping systems in the Midwestern U.S.: Potential and data gaps. Environ. Sci. Technol. 48: 4247-4256.
Fujinuma, Ryosuke., Rodney T. Venterea, and Carl Rosen. 2011. Broadcast urea reduces N2O but increases NO emissions compared with conventional and shallow-applied anhydrous ammonia in a coarse-textured soil. J. Environ. Qual. 40:1806–1815. doi:10.2134/jeq2011.0240.
Hernandez-Ramirez, G., S.M. Brouder, D.R. Smith, and G.E. Van Scoyoc. 2009. Nitrous oxide production in an Eastern Corn Belt soil: Sources and redox range. Soil Sci. Soc. Am. J. 73:1182-1191.
Hernandez-Ramirez, G., S.M. Brouder, D.R. Smith, and G.E. Van Scoyoc. 2011. Nitrogen partitioning and utilization in corn cropping systems: Rotation, N source and N timing. Eur. J. Agronomy 34: 190-195.
Halvorson, Ardell D., and Stephen J. Del Grosso. 2013. Nitrogen placement and source effects on nitrous oxide emissions and yields of irrigated corn. J. Environ. Qual. 42:312– 322; doi:10.2134/jeq2012.0315.
IPCC: Intergovernmental Panel on Climate Change Guidelines for National Greenhouse Gas Inventories. Volume 4: Agriculture, Forestry and Other Land Use, Chapter 11: N2O Emissions from Managed Soils, and CO2 Emissions from. Lime and Urea Application. 2006
Maharjan, Bijesh. Rodney T. Venterea, and Carl Rosen. 2014. Fertilizer and irrigation management effects on nitrous oxide emissions and nitrate leaching. Agron. J. 106:703–714; doi:10.2134/agronj2013.0179.
Omonode, R.A., A. Gál, D.R. Smith and T.J. Vyn*. 2010. Nitrous oxide fluxes in corn following three decades of tillage and rotation treatments. Soil Sci. Soc. Am. J. 75:
Omonode, R.A., P. Kovacs, and T.J. Vyn. 2015. Tillage and nitrogen rate effects on area and yield-scaled nitrous oxide emissions from pre-plant anhydrous ammonia. Agron. J. 107:605–614.
Venterea, Rodney T., Bijesh Maharjan, and Michael S. Dolan. 2011. Fertilizer source and tillage effects on yield-scaled nitrous oxide emissions in a corn cropping system. J. Environ. Qual. 40:1521–1531. doi:10.2134/jeq2011.0039.
Sanz-Cobena, Alberto, Laura Sánchez-Martín, Lourdes García-Torres, and Antonio Vallejo. 2012. Gaseous emissions of N2O and NO and NO3− leaching from urea applied with urease and nitrification inhibitors to a maize (Zea mays) crop. Agriculture, Ecosystems and Environment 149 (2012) 64–73; doi:10.1016/j.agee.2011.12.016.
Snyder, C.S., E.A. Davidson, P. Smith, and R.T. Venteara. 2014. Agriculture: Sustainable crop and animal production to help mitigate nitrous oxide losses. Current Opinion in Environmental Sustainability. 9-10: 46-54.