Sources and priming of soil N2O and CO2 production: Nitrogen and simulated exudate additions

Soil Science Soc of Amer J

Puurveen

et al. 2020

Improving N fertilization in croplands could minimize soil emissions of nitrous oxide (N2O) and mitigate climate change. This study investigated the effects of spring vs. fall N applications of conventional vs. enhanced‐efficiency N fertilizers (EENFs) on N2O emissions and N use efficiency in spring wheat (Triticum aestivum L.) over 2.5 yr in Alberta, Canada. Fertilizers were anhydrous ammonia and urea and the EENF formulations included urease and nitrification inhibitors and a polymer coating. We measured a fertilizer N2O emission factor of 0.31 ± 0.04%. Irrespective of N fertilizer and timing options peak N2O emissions were evident following soil thawing and major rainfalls. Because most of the annual N2O emissions were associated with soil thawing, spring‐applied N emitted half the N2O of the fall‐applied N during the second study year (P < .001). Conversely, the opposite was observed for the first study year when overall N2O emissions were 36% larger for spring‐ than fall‐applied N (P = .031) as major rainfalls occurred shortly after the spring N fertilization. Nevertheless, within this first study year, EENFs significantly reduced N2O emissions (by 26% on average; P = .019), with a tendency for 11% higher grain yield across springtime EENFs than for conventional fertilizers. Concomitantly, spring‐applied N doubled the fertilizer N recovery efficiency in the same year (P = .023). The soil at the study site inherently had high N availability (NH4 and NO3) and this probably moderated the beneficial effects of EENFs on N2O emissions and grain yields. Results suggest that spring EENFs can mitigate the risk for N2O emissions while sustaining high yields even under scenarios with high availability of native soil N.

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Nitrous oxide emissions and nitrogen use efficiency in wheat: Nitrogen fertilization timing and formulation, soil nitrogen, and weather effects

Thilakarathna

Soil Science Soc of Amer J

Puurveen

et al. 2020

“…It is uncertain whether measured N 2 O sourced from denitrification came from bacterial denitrification or nitrifier denitrification because the SP signatures of these two pathways overlap (Daly & Hernandez‐Ramirez, 2020). Bacterial denitrification uses NO 3 − as an initial substrate, whereas nitrifier denitrification uses nitrite (which is generated in an intermediate step of nitrification).…”

Section: Discussionmentioning

confidence: 99%

“…The role of perennial plants on the priming of N 2 O production from soil organic matter (SOM)‐N is just starting to be understood. Daly and Hernandez‐Ramirez (2020) recently reported that root exudation from perennial species diminished the positive priming of N 2 O derived from SOM mineralization in N‐fertilized soils. Compared with annual croplands, perennial cropping could also lower N 2 O emissions because of the greater N retention capacity of increased roots and longer growing seasons (Abraha, Gelfand, Hamilton, Chen, & Robertson, 2018; Ferchaud, Vitte, Bornet, Strullu, & Mary, 2015; Ryan et al., 2018).…”

Section: Introductionmentioning

confidence: 99%

How does management legacy, nitrogen addition, and nitrification inhibition affect soil organic matter priming and nitrous oxide production?

Thilakarathna

2020

J of Env Quality

Long‐term management of croplands influences the fluxes and sources of nitrous oxide (N2O). We examined this premise in a greenhouse study by using soils collected from a 38‐yr‐old field experiment. The sampled treatments were continuous barley (Hordeum vulgare L.; CB), continuous fescue (Festuca rubra L., F. arundinacea Schreb; CF), and two phases of an 8‐yr rotation: faba bean (Vicia faba L.; FB) and alfalfa (Medicago sativa L.)–bromegrass (Bromus inermis Leyss) hay. Barley was grown as a test crop in the greenhouse in each soil. The ranking of N2O emissions was hay > FB > CB > CF (P < .001). We quantified the 15N‐site preference to assess the N2O‐producing processes. Denitrification was the predominant source, contributing 77.4% of the N2O production. We also evaluated nitrogen (N) additions: urea alone or urea with a nitrification inhibitor (nitrapyrin or DMPSA). Compared with urea alone, nitrapyrin and DMPSA reduced N2O emissions by 16 and 25%, respectively. We used urea labeled with 15N to trace N to N2O emissions, aboveground plant N uptake, and N retention by soils. Total 15N‐recovery (N2O + plant + soil) was highest under FB (86%) and lowest under CB (29%). We further separated the N2O derived from urea versus N2O from soil organic matter (SOM). The inhibitor DMPSA reduced the N2O derived specifically from added urea‐N by more than half (P < .001). With the addition of urea, N2O production from mineralization of SOM‐N accelerated over the control (without urea), termed the priming effect. This priming of SOM‐N contributed with 13% of the total N2O production when averaged across the four management legacies. The CB soil had the highest proportion of priming‐derived N2O (24%). Management legacies clearly differed in soil carbon and N, which governed N2O production from denitrification and SOM priming.

Sources and priming of nitrous oxide production across a range of moisture contents in a soil with high organic matter

Roman‐Perez

2020

J of Env Quality

Adding nitrogen fertilizers to agricultural soils contributes to increasing concentrations of nitrous oxide (N2O) in the atmosphere. However, the impacts of N addition on soil organic matter (SOM) turnover, SOM availability, and the ensuing SOM‐derived N2O emissions remain elusive. Within this context, the net change in direction and rate of SOM‐derived N2O production triggered by added N is termed the N2O priming effect. This incubation study examined the sources and priming of N2O production as a function of urea addition and multiple moisture contents in a soil with high SOM (55 g organic C kg−1). We assessed four water‐filled pore space (WFPS) conditions: 28, 40, 52, and 64%. Relative to controls receiving no N, urea addition increased N2O production by 2.6 times (P < .001). Cumulative N2O production correlated well with nitrification rates (r = .75; P = .03). We used 15N‐labeled urea to trace the added urea into N2O. Of the N added via urea, the recovery as N2O–N shifted from 0.02 to 0.17% when WFPS increased from 28 to 64% (P < .05). We also partitioned the N2O production into urea vs. SOM sources. More N2O was sourced from SOM than urea, with 59 ± 2% N2O originating from SOM. The magnitude of SOM‐derived N2O under urea was larger than that of the control, revealing that positive N2O priming was triggered by urea addition. Upon subtracting the controls, the primed N2O was a consistent 19 ± 2% of the total N2O produced by urea‐amended soils. Nevertheless, the priming magnitude rose sharply with increasing moisture by more than one order of magnitude from 4 to 48 μg N2O–N kg−1 soil and in exponential mode (R2 = .98). Soil moisture, SOM, and nitrification interacted to drive the sources and priming of N2O.