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

Abstract

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.

Nonlinear turnover rates of soil carbon following cultivation of native grasslands and subsequent afforestation of croplands

“…Furthermore, Quesada et al (2020) recently discussed the mechanisms for soil C accretion in tropical forests. In line with earlier findings by Wang et al (2016), Quesada et al (2020) stated that SOM physical protection provided by the formation of soil aggregates slows decomposition of SOM within aggregates; hence, it becomes a second layer of stabilization after realizing the primary SOM stabilizing effects caused by mineral surfaces of fine soil particles such as silt and clay. Further studies can focus on the effects of inherent mineralogy and texture as well as clay lessivage processes on C dynamics and storage in afforested soils (Chendev et al, 2020;Quesada et al, 2020).…”

“…For instance, removing C from the atmosphere is a paramount contribution by trees (Guo and Gifford, 2002;Li et al, 2012Li et al, , 2018. In effect, soil C accrual (Paul et al, 2002;Dhillon and Van Rees, 2017;Khaleel et al, 2020) and stabilization (Hernandez-Ramirez et al, 2011;Wang et al, 2016;Quesada et al, 2020) beneath trees have been recognized as an effective means of sequestering atmospheric C. In addition to soil accruals, diverse microbial communities can flourish beneath mature trees (Kiani et al, 2017). Additional functions by tree vegetation include improving air quality, enhanced microclimate, and erosion control (Sauer et al, 2007;Hernandez-Ramirez et al, 2012;Chendev et al, 2015b).…”

Increased N2O Production from Soil Organic Matter Following a Simulated Fall-Freeze-Thaw Cycle: Effects of Fall Urea Addition, Soil Moisture, and History of Manure Applications

“…In addition to the priming of SOM-N caused by labile N additions, soils can be predisposed to 430 exhibiting inherent priming because of the legacy effects from earlier management choices 431 (Ginting et al 2003, Blagodatskaya et al 2007, Thilakarathna and Hernandez-Ramirez 2021. It is plausible that the manured soils (SW) in our study showed a more intense response of primed N2O dynamics to the fall-applied urea because the previous field manure injections in this soil had increased the easily decomposable SOM.…”

“…More than half of the anthropogenic sources of N2O are linked to agricultural landscapes (Parry et al 2007, Intergovernmental Panel on Climate Change 2013, Chai et al 2020, where manure and synthetic N fertilizers are recurrently applied (Lin et al 2017, Grant et al 2020, Thilakarathna et al 2020. Such N additions not only provide substrates for N2O emissions directly, but they can also stimulate mineralization of pre-existing SOM, which would subsequently lead to additional N2O emissions indirectlya response termed the 'priming effect' (Thilakarathna and Hernandez-Ramirez 2021). In other words, in the case of N2O emissions from soils, priming consists of the fertilizer-induced N2O emissions that originate from SOM mineralization.…”

“…The difference between α and β can be expressed as SP=  15 N α - 15 N  Yoshida 1999, Yamamoto et al 2017). When N2O fluxes become sufficiently large, this SP analytical approach enables us to examine and apportion the major N2O producing pathways (i.e., nitrification vs. bacterial denitrification) (Zimmerman et al 2011, Daly and Hernandez-Ramirez 2020, Thilakarathna and Hernandez-Ramirez 2021.…”