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

Abstract

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.

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

“…Similarly, Thilakarathna et al. (2020) recently reported soil N saturation in fertile annual croplands, which also translated into elevated field N 2 O emissions and plant productivity irrespective of N fertilization choices.…”

“…Earlier studies of N 2 O emissions from soils have mostly focused on in‐season management effects (Chai et al., 2020; Thilakarathna et al., 2020). Our study provides several new insights into how management legacies from previous seasons drive differences in pulses of N 2 O emissions.…”

“…As a greenhouse gas, N 2 O is 300 times more potent than CO 2 , and it is also a substrate in reactions that deplete the stratospheric ozone layer (Lin et al., 2017; Parry et al., 2007). Within agroecosystems, N management options interact with numerous soil biotic and abiotic factors to drive the outcome of N 2 O fluxes (Abalos et al., 2016; Thilakarathna et al., 2020). Furthermore, the combined effect of plant and microbial utilization of soil organic C, N, water and oxygen intricately affects N 2 O production.…”

“…Nitrification inhibitors can be used to diminish N 2 O losses (Grant, Lin, & Hernandez‐Ramirez, 2020; Thilakarathna et al., 2020) by blocking the ammonia monooxygenase enzyme and delaying the oxidation of ammonium (NH 4 + ) (Guardia et al., 2017; Recio, Alvarez, Rodriguez‐Quijano, & Vallejo, 2019). Common inhibitors are nitrapyrin and 3,4‐dimethylpyrazole phosphate, which can reduce N 2 O emissions by 50% (Lin et al., 2017; Ruser & Schulz, 2015).…”

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

“…Among the synthetic N fertilizers, urea is the most commonly used formulation worldwide (FAO, 2020), with annual applications to a broad range of agricultural systems (Chai et al., 2020; Thilakarathna et al., 2020). Therefore, it is pertinent to examine the priming effects of SOM availability on N 2 O production caused by typical urea applications.…”