Search

The fertilization regimes of combining manure with synthetic fertilizer are benefits for crop yields and soil fertility in cropping systems as compared to sole synthetic fertilization, but the responses of nitrous oxide (N 2 O) emissions to these practices are inconsistent in the literatures. We hypothesized that it is caused by different proportions of nitrogen (N) applied as manure and various soil properties. Here, we conducted a microcosm experiment, and measured the N 2 O emissions from control (no N) and five manure substitution treatments (supplied 100 mg N kg -1 using the combination of urea with manure) with a range of proportions of N applied as manure (0, 25%, 50%, 75%, and 100%) in three different soil types (fluvo-aquic soil, black soil, and latosol) under aerobic condition. The stimulated effect on N 2 O emissions was more pronounced after manure application in an alkaline soil with high nitrification rate, due to relatively rapid soil DOC depletion and N mineralization of manure. N 2 O emissions from partial substitution of urea with manure were significantly higher than manure-only addition under high soil pH due to abundant labile C from manure. However, there was no difference between manure substitution treatments under acid soils. Nitrification inhibitor substantially decreased N 2 O emissions with increasing soil pH, but it was less effective in mitigating N 2 O emissions with larger proportion of manure. This is likely due to the slow nitrification under low soil pH, and denitrification derived N 2 O increased with increasing manure application rate. Collectively, our study shows that the application of manure substitution to alkaline soils requires careful consideration, which might have rapid nitrification potential and hence trigger significant N 2 O emissions. The knowledge gained in this work will help the decision-makers in optimizing a sound N fertilization regime interacted with soil properties for sustainable crop production and N 2 O mitigation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Hot moments of nitrous oxide (N 2 O) emissions induced by interactions between weather and management make a major contribution to annual N 2 O budgets in agricultural soils. The causes of N 2 O production during hot moments are not well understood under field conditions, but emerging evidence suggests that short-term fluctuations in soil oxygen (O 2 ) concentration can be critically important. We conducted high time-resolution field observations of O 2 and N 2 O concentrations during hot moments in a dryland agricultural soil in Northern China. Three typical management and weather events, including irrigation (Irr.), fertilization coupled with irrigation (Fer.+Irr.) or with extreme precipitation (Fer.+Pre.), were observed. Soil O 2 and N 2 O concentrations were measured hourly for 24 h immediately following events and measured daily for at least one week before and after the events. Soil moisture, temperature, and mineral N were simultaneously measured. Soil O 2 concentrations decreased rapidly within 4 h following irrigation in both the Irr. and Fer.+Irr. events. In the Fer.+Pre. event, soil O 2 depletion did not occur immediately following fertilization but began following subsequent continuous rainfall. The soil O 2 concentration dropped to as low as 0.2% (with the highest soil N 2 O concentration of up to 180 ppmv) following the Fer.+Pre. event, but only fell to 11.7% and 13.6% after the Fer.+Irr. and Irr. events, which were associated with soil N 2 O concentrations of 27 ppmv and 3 ppmv, respectively. During the hot moments of all three events, soil N 2 O concentrations were negatively correlated with soil O 2 concentrations (r = -0.5, P < 0.01), showing a quadratic increase as soil O 2 concentrations declined. Our results provide new understanding of the rapid short response of N 2 O production to O 2 dynamics driven by changes in soil environmental factors during hot moments. Such understanding helps improve soil management to avoid transitory O 2 depletion and reduce the risk of N 2 O production., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Oxygen (O 2 ) plays a critical and yet poorly understood role in regulating nitrous oxide (N 2 O) production in well-structured agricultural soils. We investigated the effects of in situ O 2 dynamics on N 2 O production in a typical intensively managed Chinese cropping system under a range of environmental conditions (temperature, moisture, ammonium, nitrate, dissolved organic carbon, and so forth). Climate and management (fertilization, irrigation, precipitation, and temperature), and their interactions significantly affected soil O 2 and N 2 O concentrations ( P < 0.05). Soil O 2 concentration was the most significant factor correlating with soil N 2 O concentration ( r = -0.71) when compared with temperature, water-filled pore space, and ammonium concentration ( r = 0.30, 0.25, and 0.26, respectively). Soil N 2 O concentration increased exponentially with decreasing soil O 2 concentrations. The exponential model of N treatments and fertilization with irrigation/precipitation events predicted 74-90% and 58% of the variance in soil N 2 O concentrations, respectively. Our results highlight that the soil O 2 status is the proximal, direct, and the most decisive environmental trigger for N 2 O production, outweighing the effects of other factors and could be a key variable integrating the aggregated effects of various complex interacting variables. This study offers new opportunities for developing more sensitive approaches to predicting and through appropriate management interventions mitigating N 2 O emissions from agricultural soils.

The properties of agricultural soils in various regions of the world are variable and can have a significant but poorly understood impact on soil nitrogen (N) transformations and nitrous oxide (N 2 O) emissions. For this reason, we undertook a study of gross N transformations and related N 2 O emissions in contrasting agricultural soils from China and the UK. Seven Chinese and three UK agricultural soils were collected for study using a 15 N tracing approach. The soil pH ranged from 5.4 to 8.7, with three acidic soils collected from Jinjing, Lishu and Boghall; one neutral soil collected from Changshu, and the other six alkaline soils collected from Quzhou, Zhangye, Changwu, Jinzhong, Boxworth and Stetchworth. Our results showed that the main N transformation processes were oxidation of ammonium (NH 4 + ) to nitrate (NO 3 - ) (O NH4 ), and mineralization of organic N to NH 4 + . The gross autotrophic nitrification rates calculated in the three acidic soils were between 0.25 and 4.15 mg N kg -1  d -1 , which were significantly lower (p < 0.05) than those in the remaining neutral and alkaline soils ranging from 6.94 to 14.43 mg N kg -1  d -1 . Generally, soil pH was positively correlated (p < 0.001) with gross autotrophic nitrification rate and cumulative N 2 O emissions, indicating that soil pH was an important factor regulating autotrophic nitrification and N 2 O emissions. There was also a significant positive correlation between the gross autotrophic nitrification rate and cumulative N 2 O emissions, highlighting the importance of this process for producing N 2 O emissions in these agricultural soils under aerobic conditions. Gross NH 4 + immobilization rates were very low in most soils except for the Jinjing soil with the lowest pH. In conclusion, the gross autotrophic nitrification rates and related N 2 O emissions were controlled by soil pH irrespectively of the soil's origin in these agricultural soils., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The IPCC assume a linear relationship between nitrogen (N) application rate and nitrous oxide (N 2 O) emissions in inventory reporting, however, a growing number of studies show a nonlinear relationship under specific soil-climatic conditions. In the North China plain, a global hotspot of N 2 O emissions, covering a land as large as Germany, the correlation between N rate and N 2 O emissions remains unclear. We have therefore specifically investigated the N 2 O response to N applications by conducting field experiments with five N rates, and high-frequency measurements of N 2 O emissions across contrasting climatic years. Our results showed that cumulative and yield-scaled N 2 O emissions both increased exponentially as N applications were raised above the optimum rate in maize ( Zea mays L.). In wheat ( Triticum aestivum L.) there was a corresponding quadratic increase in N 2 O emissions with the magnitude of the response in 2012-2013 distinctly larger than that in 2013-2014 owing to the effects of extreme snowfall. Existing empirical models (including the IPCC approach) of the N 2 O response to N rate have overestimated N 2 O emissions in the North China plain, even at high N rates. Our study therefore provides a new and robust analysis of the effects of fertilizer rate and climatic conditions on N 2 O emissions.

Arable soil continues to be the dominant anthropogenic source of nitrous oxide (N2O) emissions owing to application of nitrogen (N) fertilizers and manures across the world. Using laboratory and in situ studies to elucidate the key factors controlling soil N2O emissions remains challenging due to the potential importance of multiple complex processes. We examined soil surface N2O fluxes in an arable soil, combined with in situ high‐frequency measurements of soil matrix oxygen (O2) and N2O concentrations, in situ 15N labeling, and N2O 15N site preference (SP). The in situ O2 concentration and further microcosm visualized spatiotemporal distribution of O2 both suggested that O2 dynamics were the proximal determining factor to matrix N2O concentration and fluxes due to quick O2 depletion after N fertilization. Further SP analysis and in situ 15N labeling experiment revealed that the main source for N2O emissions was bacterial denitrification during the hot‐wet summer with lower soil O2 concentration, while nitrification or fungal denitrification contributed about 50.0% to total emissions during the cold‐dry winter with higher soil O2 concentration. The robust positive correlation between O2 concentration and SP values underpinned that the O2 dynamics were the key factor to differentiate the composite processes of N2O production in in situ structured soil. Our findings deciphered the complexity of N2O production processes in real field conditions, and suggest that O2 dynamics rather than stimulation of functional gene abundances play a key role in controlling soil N2O production processes in undisturbed structure soils. Our results help to develop targeted N2O mitigation measures and to improve process models for constraining global N2O budget. [ABSTRACT FROM AUTHOR]

Soil nitrous oxide (N2O) is an important greenhouse gas contributing to climate change. Many processes produce N2O in soil and the production rate of each process is affected by climatic-edaphic factors, making the soil-to-atmosphere N2O flux extremely dynamic. Experimental approaches, including natural and enriched isotopic methods, have been developed to separate and quantify the N2O production from different processes. However, these methods are often costly and tedious, hampering their wide application. This study aimed to develop a mechanistic model quantifying the soil N2O production from nitrifier nitrification (NN), nitrifier denitrification (ND), and heterotrophic denitrification (HD), which are considered as the most important biological processes, and to investigate how climatic-edaphic factors affect N2O production from individual process as well as total N2O production. The developed model demonstrated its robustness and capability by reliably reproducing the N2O production from NN, ND, and HD in different types of soils under various moisture contents or oxygen concentrations. The model simulations unraveled how environmental conditions and soil properties control the total N2O production rate by variably regulating individual processes. Therefore, the mechanistic model can potentially elucidate the large spatiotemporal variances of in-situ soil N2O flux and improve the assessment of soil N2O emission at regional and global scales. [ABSTRACT FROM AUTHOR]

Digestate is considered as an option for recycling resources and a part of the substitution for chemical fertilizers to reduce environmental impacts. However, its application may lead to significant nitrous oxide (N 2 O) emissions because of its high concentration of ammonium and degradable carbon. The research objectives are to evaluate how N 2 O emissions respond to digestate as compared to urea application and whether this depends on soil properties and moisture. Either digestate or urea (100 mg N kg−1) was applied with and without a nitrification inhibitor of 3,4-dimethylpyrazole phosphate (DMPP) to three soil types (fluvo-aquic soil, black soil, and latosol) under three different soil moisture conditions (45, 65, and 85% water-filled pore space (WFPS)) through microcosm incubations. Results showed that digestate- and urea-induced N 2 O emissions increased exponentially with soil moisture in the three studied soils, and the magnitude of the increase was much greater in the alkaline fluvo-aquic soil, coinciding with high net nitrification rate and transient nitrite accumulation. Compared with urea-amended soils, digestate led to significantly higher peaks in N 2 O and carbon dioxide (CO 2) emissions, which might be due to stimulated rapid oxygen consumption and mineralized N supply. Digestate-induced N 2 O emissions were all more than one time higher than those induced by urea at the three moisture levels in the three studied soils, except at 85% WFPS in the fluvo-aquic soil. DMPP was more effective at mitigating N 2 O emissions (inhibitory efficacy: 73%–99%) in wetter digestate-fertilized soils. Overall, our study shows the contrasting effect of digestate to urea on N 2 O emissions under different soil properties and moisture levels. This is of particular value for determining the optimum of applying digestate under varying soil moisture conditions to minimize stimulated N 2 O emissions in specific soil properties. [Display omitted] • N 2 O emission ratios of digestate to urea were all more than 1 except at 85% WFPS in alkaline soil. • High soil moisture triggered an exponential increase in N 2 O emissions from digestate amendment. • The greater increase in alkaline soil was due to high net nitrification rate and transient nitrite accumulation. • Nitrification inhibitor significantly reduced digestate-induced N 2 O emissions under high soil moisture conditions. [ABSTRACT FROM AUTHOR]

Optimizing crop rotations is one of the proposed sustainable management strategies for increasing carbon sequestration. The main aim of this study was to evaluate the DeNitrification-DeComposition (DNDC) model for estimating soil parameters (temperature, moisture and exchangeable NO3− and NH4+), crop yield and nitrous oxide (N2O) emissions for long-term multi-cropping systems in Hebei, China. The model was validated using five years of data of soil parameters, crop yields and N2O emissions. The DNDC model effectively simulated daily soil temperature, cumulative soil nitrogen and crop yields of all crops. It predicted the trends of observed daily N2O emissions and their cumulative values well but overestimated the magnitude of some peaks. However, the model underestimated daily water filled pore space, especially in dry seasons, and had difficulties in correctly estimating daily exchangeable NO3− and NH4+. Both observed and simulated cumulative N2O results showed that optimized and alternative cropping systems used less nitrogen fertiliser, increased grain yield and decreased N2O emissions compared to the conventional cropping system. Our study shows that although the DNDC model (v. 9.5) is not perfect in estimating daily N2O emissions for these long-term multi-cropping systems, it could still be an effective tool for predicting cumulative emissions. [ABSTRACT FROM AUTHOR]

Enhanced efficiency nitrogen fertilizers (EENFs) have provided opportunities for the simultaneous mitigation of nitrous oxide (N 2 O) emissions and increases in crop productions. However, the practice of combining EENFs with optimal fertilization under conditions of misaligned water and fertilizer inputs in rain-fed spring maize systems remains inadequately understood. This study aims to determine the factors controlling N 2 O emissions under the soil climatic conditions in rain-fed plastic mulching cropping systems treated with different nitrogen (N) fertilization rates and EENFs, and to determine the most effective N fertilization measure to reduce N 2 O emissions while maintaining crop yields. A 3-year field experiment was conducted in a spring maize system located in the semiarid rain-fed region of the Loess Plateau, applying two types of EENFs: a nitrification inhibitor dicyandiamide (DCD) and a slow-release fertilizer (SRF). It comprised five fertilization treatments: unfertilized (CK), conventional N rate (CON, 200 kg N ha−1), optimal N rate (OPT, 160 kg N ha−1), OPT with the addition of DCD (OPT+DCD), and OPT using SRF (OPT-SRF). The average annual cumulative N 2 O emissions over the 3-year experimental period ranged from 0.74 to 1.87 kg N 2 O-N ha–1. Fertilizer N contributed 26−60% to annual N 2 O emissions. The highest N 2 O fluxes (50–161 μg N 2 O-N m–2 h–1) typically occurred within the initial 10 days following fertilization, likely induced by strong nitrification processes, constituting 12–19% of the annual N 2 O emissions during this brief period. In comparison to the CON treatment, the OPT, OPT+DCD, and OPT-SRF treatments resulted in significant reductions in annual N 2 O emissions of 24%, 46%, and 34%, respectively, without causing any significant decrease in maize grain yields. The application of DCD led to increased ammonium (NH 4 +-N) concentrations while reducing nitrate (NO 3 –-N). Conversely, using SRF resulted in a decrease in both NH 4 +-N and NO 3 –-N concentrations. Using EENFs at the ideal fertilization rate significantly curtailed yearly N 2 O emissions without adversely affecting maize yields in a rain-fed plastic mulching spring maize system prevalent in the Loess Plateau. Most N 2 O emissions occurred post-fertilization, with rainfall events further influencing these emissions. Our findings recommend the incorporation of nitrification inhibitors, such as DCD, as the most effective fertilizer measure for reducing N 2 O emissions in the rain-fed region of the Loess Plateau. [ABSTRACT FROM AUTHOR]