Nitrification inhibitors reduce N2O emissions induced by application of biogas digestate to oilseed rape

Nitrogen fertilizers are the major source of nitrous oxide (N2O) emissions from arable land. The addition of nitrification inhibitors to fertilizers may improve the nitrogen (N) use efficiency and reduce N2O emissions. However, it is still unclear how crop rotations affect nitrification and urease inhibitors to reduce N2O emissions. We conducted a field experiment with two-year winter wheat and one-year oilseed rape cultivation in Germany from 2016 to 2017. We applied five different fertilizer treatments: (1) a control treatment without fertilization (N0); (2) calcium ammonium nitrate (CAN); (3) ammonium sulfate nitrate with the nitrification inhibitor 3,4-dimethylepyrazole phosphate (ENTEC); (4) urea; and (5) urea with the urease inhibitor N-(n-butyl) thiophosphoric triamide (UTEC). Crop yield, grain and straw N content, and N2O fluxes were measured to assess yield-scaled N2O emissions under different treatments. We found that in all fertilized treatments, the aboveground N uptake of wheat after wheat was 199–203 kg N ha−1, which was much lower than that of wheat after oilseed rape (252–271 kg N ha−1). The apparent N recovery of oilseed rape (13–23%) was much lower than in wheat after wheat (63–66%). The enhanced-efficiency fertilizers increased aboveground N uptake by 0–5% compared to fertilizers without inhibitors. The oilseed rape field had the highest yield-scaled N2O emissions (18.0, 15.1, 16.7 and 15.6 g N2O-N kg−1 aboveground N uptake in CAN, ENTEC, urea and UTEC, respectively). These results indicate that urease and nitrification inhibitors hold the potential to increase crop yield and reduce N2O emissions. Oilseed rape straw should be carefully managed to avoid high N2O emissions. Future research should be focused on different fertilizer level and optimized N application strategy to increase the efficiency of urease and nitrification inhibitors, for instance, by increasing the N application rate in wheat after wheat, but reducing it in oilseed rape.

Mitigation of yield-scaled nitrous oxide emissions and global warming potential in an oilseed rape crop through N source management

The sub-project of the project “Minderung von Treibhausgasemissionen im Rapsanbau unter besonderer Berücksichtigung der Stickstoffdüngung” of the division Plant Nutrition and Crop Physiology, Department of Crop Sciences of Georg-August University focused on steps in the nitrogen cycle that produce or interfere with N2O emissions from soils. It addressed the question of how the N cycle is modified by a winter oilseed rape – winter wheat – winter barley crop rotation. The focus of the doctoral thesis was put on the post-harvest period and the production of N2O emissions in winter oilseed rape. Several lab and field experiments were conducted: (1) Incubation experiment using oilseed rape and 15N-labelled barley straw; An incubation experiment carried out under controlled conditions aimed at comparing N addition and different straw qualities for their potential to provoke N2O emissions from soil. Treatments consisted of non-treated control soil (CK), 15N labelled barley straw (BST), oilseed rape straw (RST), 15N labelled barley straw + mineral N (BST+N), or oilseed rape straw + mineral N (RST+N). N fertilizer was applied to the soil surface as calcium ammonium-nitrate at a rate of 67.5 mg N kg-1 soil equiv. to 100 kg N ha-1 and soil moisture was adjusted to 80% water-holding capacity. The experiment covered a measurement period of 43 days. Cumulative N2O emissions in this study summed up to 3, 19, 26, 439 and 387µg N2O-N kg-1 soil 43 days-1 for CK, BST, RST, BST+N and RST+N. Application of mineral N fertilizer to the straw amended soils enhanced N2O emissions considerably in BST+N and RST+N treatments masking the effect of straw type. 15N labeling showed that only about 0.72% and 0.46% of the emitted N2O originated from straw-N in the BST and BST+N treatments after 22 days indicating a very low share of straw-borne N to the formation of N2O emissions. In agricultural practice, an N fertilization to soils amended with C-rich residues in the post-harvest period could lead to high N2O emissions. (2) Post-harvest N2O emissions as affected by N fertilizer and straw management – 2 year study at the site Reinshof; Management options to mitigate N2O emissions in oilseed rape cropping were tested in a 2-year field experiment at the field site Reinshof of the Faculty of Agricultural Sciences of Georg-August University of Goettingen. The treatments included a reduced spring N fertilization rate (1/2 of current recommendation), N fertilization of 180 kg N ha-1 and oilseed rape straw removal after harvest. N2O sampling was done from oilseed rape harvest to the beginning of the following growth season. The COUP model (Coupled heat and mass transfer model for the soil-plant-atmosphere system) was employed to uncover possible mechanisms of N2O emissions. In 2013, cumulative August-March N2O emissions ranged between 0.46±0.05 kg N2O-N ha-1 (0 kg N ha-1, with straw removal) and 1.05±0.1 kg N2O-N ha-1 (180 kg N ha-1 with straw application) whereas in 2014 N2O emissions were clearly higher accounting for 4.06±0.34 (90 kg N ha-1, with straw application) und 7.33±0.24 kg N2O-N ha-1 (unfertilized control soil with straw incorporation). There was no statistically significant effect of fertilization (p>0.05), but straw removal compared to straw incorporation slightly increased N2O emissions. In contrast to management measures, soil temperature and soil moisture showed a large influence on the rates of N2O emissions. The modeling approach indicated the importance of decomposition activity. Decomposition accelerated N cycling and in particular denitrification rates with high N2O emissions. (3) Field studies in five regions of Germany in a winter oilseed rape – winter wheat – winter barley crop rotation; For a detailed evaluation of N2O emissions in important oilseed rape cropping regions of Germany, 5 field experimental sites across Germany – Berge, Dedelow, Ihinger Hof, Hohenschulen and Merbitz – were chosen. To allow comparability, the crops were grown simultaneously from December 2012 to October 2015. Various parameters like soil temperature and water-filled pore space (WFPS) were recorded and N2O emissions were measured in the crops oilseed rape, wheat and barley and yield-related N2O emissions were calculated. To assess the impact of abiotic factors and crops, a generalized additive model was set up. The generalized additive model revealed that the abiotic factors drove N2O emissions. The impact of environmental drivers like temperature and WFPS on N2O emissions varied depending on site, but not by crop type. Fertilizer-related N2O emissions across all five sites were 0.76, 0.74 and 0.76% of the applied fertilizer N for oilseed rape, winter wheat and winter barley, respectively. N2O emissions from non-fertilized soils were not considered in this approach. Generally, the thesis demonstrated the dependence of N2O emissions on a set of factors in the post-harvest period. The factor's level of importance changed as they were varying in magnitude. Management options have to be reevaluated and adopted to fit a changing climate.

Overwintering of pollen beetles and their predators in oilseed rape and semi-natural habitats

Nitrous oxide emissions from oilseed rape cultivation were unaffected by flash pyrolysis biochar of different type, rate and field ageing

Improving the management of mineral fertilizers for nitrous oxide mitigation: The effect of nitrogen fertilizer type, urease and nitrification inhibitors in two different textured soils

Field cropping practices in Canada include routine use of nitrogen (N) fertilizer, which produces substantial amounts of nitrous oxide (N2O) emissions. Adoption of improved N management practices may reduce both the amount of N applied and these N2O emissions. Using flux-tower field measurements, we investigated how dual inhibitors (urease and nitrification inhibitors with urea) reduced N fertilizer-induced N2O emissions, compared with urea only, in eastern Canada across 7 years. We also used meta-analysis (of static chamber studies) to examine how inhibitors and other enhanced efficiency fertilizers (EEFs), along with other improved N management techniques, affected fertilizer-induced N2O emissions from Canadian agricultural cropping systems. From the field study, the dual inhibitors reduced growing season N2O emissions by 22% and annual N2O emissions by 10% for high N application rates to corn (Zea mays), while N2O emissions from lower N applications to wheat (Triticum aestivum) showed no differences between the EEF and urea. Crop yields for both the corn and wheat were similar between the different N fertilizer treatments. Across Canada, the meta-analysis showed that EEFs (which include coated slow-release fertilizers and both nitrification and urease inhibitors combined and on their own), on average, reduced N2O emissions by 11%. Nitrification inhibitors (alone or in combination with urease inhibitors) averaged a 19% reduction in N2O emissions. Most of the studies used in the meta-analysis had minimal sampling through the non-growing season though, so the total annual N2O emission reductions were not evaluated and may actually be lower. The meta-analysis indicated that the most effective N management techniques for reducing N2O emissions were the use of EEFs, split application of N fertilizers and the use of organic fertilizers, with the effectiveness of these practices all strongly influenced by soil and weather conditions. The meta-analysis also found that reductions with EEFs from studies that included year-round measurements, tended to be less than studies that included only the growing season. This suggests that when improved N management practices use the same N application rates as the regular practice, more residual N may be available for non-growing season losses. As a result, when no yield benefit is noted, these improved practices should be combined with N rate reductions.

Abstract. Reductions in N2O emissions from nitrification inhibitors (NI) are substantial but remain uncertain because measurements of N2O emissions are highly variable and discontinuous. Mathematical modelling may offer an opportunity to estimate these reductions if the processes causing variability in N2O emissions can be accurately simulated. In this study, the effect of NI was simulated with a simple, time-dependent algorithm to slow NH4+ oxidation in the ecosystem model ecosys. Slower nitrification modelled with NI caused increases in soil NH4+ concentrations and reductions in soil NO3- concentrations and in N2O fluxes that were consistent with those measured following fall and spring applications of slurry over 2 years from 2014 to 2016. The model was then used to estimate direct and indirect effects of NI on seasonal and annual emissions. After spring slurry applications, NI reduced N2O emissions modelled and measured during the drier spring of 2015 (35 % and 45 %) less than during the wetter spring of 2016 (53 % and 72 %). After fall slurry applications, NI reduced modelled N2O emissions by 58 % and 56 % during late fall in 2014 and 2015 and by 8 % and 33 % during subsequent spring thaw in 2015 and 2016. Modelled reductions were consistent with those from meta-analyses of other NI studies. Simulated NI activity declined over time so that reductions in N2O emissions modelled with NI at an annual timescale were relatively smaller than those during emission events. These reductions were accompanied by increases in NH3 emissions and reductions in NO3- losses with NI that caused changes in indirect N2O emissions. With further parameter evaluation, the addition of this algorithm for NI to ecosys may allow emission factors for different NI products to be derived from annual N2O emissions modelled under diverse site, soil, land use and weather.

Inhibitors mitigate N2O emissions more effectively than biochar: A global perspective

Urea fertilizer‐induced N2O emissions from soils might be reduced by the addition of urease and nitrification inhibitors. Here, we investigated the effect of urea granule (2–3 mm) added with a new urease inhibitor, a nitrification inhibitor, and with a combined urease inhibitor and nitrification inhibitor on N2O emissions. For comparison, the urea granules supplied with or without inhibitors were also used to prepare corresponding supergranules. The pot experiments without vegetation were conducted with a loess soil at (20 ± 2)°C and 67% water‐filled pore space. Urea was added at a dose of 86 kg N ha–1 by surface application, by soil mixing of prills (<1 mm) and granules, and by point‐placement of supergranules (10 mm) at 5 cm soil depth. A second experiment was conducted with spring wheat grown for 70 d in a greenhouse. The second experiment included the application of urea prills and granules mixed with soil, the point‐placement of supergranules and the addition of the urease inhibitor, and the combined urease plus nitrification inhibitors at 88 kg N ha–1. In both experiments, maximum emissions of N2O appeared within 2 weeks after fertilization. In the pot experiments, N2O emissions after surface application of urea were less (0.45% to 0.48% of total fertilization) than from the application followed by mixing of the soil (0.54% to 1.14%). The N2O emissions from the point‐placed‐supergranule treatment amounted to 0.64% of total fertilization. In the pot experiment, the addition of the combined urease plus nitrification inhibitors, nitrification inhibitor, and urease inhibitor reduced N2O emissions by 79% to 87%, 81% to 83%, and 15% to 46%, respectively, at any size of urea application. Also, the N2O emissions from the surface application of the urease‐inhibitor treatment exceeded those of the granules mixed with soil and the point‐placed‐supergranule treatments receiving no inhibitors by 32% to 40%. In the wheat growth experiment, the N2O losses were generally smaller, ranging from 0.16% to 0.27% of the total fertilization, than in the pot experiment, and the application of the urease inhibitor and the combined urease plus nitrification inhibitors decreased N2O emissions by 23% to 59%. The point‐placed urea supergranule without inhibitors delayed N2O emissions up to 7 weeks but resulted in slightly higher emissions than application of the urease inhibitor and the urease plus nitrification inhibitors under cropped conditions. Our results imply that the application of urea fertilizer added with the combined urease and nitrification inhibitors can substantially reduce N2O emissions.

Nitrous oxide (N2O) is a powerful greenhouse gas and has an adverse effect on stratospheric ozone. Field application of synthetic N fertilizers is the largest source of global N2O emission and different N forms (nitrate vs. ammoniacal N) may play a significant role. In addition, the use of nitrification inhibitor (NI) is considered as a reliable way to mitigate agricultural N2O emission, whereas this effect is still debated for urease inhibitors (UI). However, the efficacy of NI or UI is still variable among different inhibitor products and environmental conditions. This study was conducted to test the efficacy of N form (calcium ammonium nitrate CAN vs. urea) and the almost unstudied UI, N-(2-nitrophenyl) phosphoric triamide (2-NPT), as well as an NI, mixture of dicyandiamide and 1H-1,2,4-triazol (DCD/TZ) and the combination of both inhibitors on N2O emission and crop yield. The measurements were carried out in winter wheat growth season in the subsequent years of 2012–2013 in the North of Germany. No difference in cumulated N2O emissions were observed between urea and CAN. The results confirmed the positive effect of NI (DCD/TZ) on reducing N2O emission. Compared with untreated urea, NI addition caused ∼75 % reduction of fertilizer derived N2O emissions within the vegetation period. The combination of UI and NI did not result in a further reduction of relative or yield-scaled N2O emission, although it resulted in higher grain yield and nitrogen recovery. Addition of UI showed no consistent effect on N2O emission compared to untreated urea, however in year 2013 a significant reduction of fertilizer derived emissions by ∼50 % was observed. Higher yields were observed for CAN fertilization compared to urea, though not significant. For both treatments including UI the yield effects, in particular N use efficiency, were stronger than for untreated urea and urea solely treated with NI. Therefore, the combined treatment with UI and NI was the most advantageous fertilizer solution for concomitantly achieving high yield, high nitrogen utilization efficiency and N2O emission reduction.

Urea (U) is the most important nitrogen (N) fertilizer in agriculture worldwide, and as N fertilizer can result in large gaseous losses of NH3 and N2O. Thus, urease inhibitors (UIs) and nitrification inhibitors (NIs) have been coupled with U fertilizers to mitigate NH3 and N2O emissions. However, it is still unclear whether adding NIs and/or UIs to U stimulates other pollutants, while reducing one pollutant. Furthermore, part of the NH3 deposition to earth is converted to N2O, leading to indirect N2O emission. To estimate direct and indirect effect of UIs and NIs on the N2O-N and NH3-N losses from U; therefore, we analyzed multi-year field experiments from the same site during 2004 to 2005 and 2011 to 2013. The field experiments with U fertilization with or without UI (IPAT, N-isopropoxycarbonyl phosphoric acid triamide) and NI (DCD/TZ, Dicyandiamide/1H-1, 2, 4-Triazol) in winter wheat and with calcium ammonium nitrate (CAN) were conducted in southern Germany. Fluxes of NH3 or N2O emissions were determined following each split N fertilization in separate experiments on the same site. Our results showed that U with NIs considerably reduced N2O emissions, and adding UIs decreased NH3 emissions. However, the effect on N2O emissions exerted by (U + UIs) or (U + UIs + NIs) was inconsistent. In contrast to the treatment of (U + UIs + NIs), the addition of NIs alone to U stimulated NH3 emission compared to treatment with U. When 1% indirect N2O emission from NH3 (IPCC emission factor (EF4)) was considered to estimate the indirect N2O emission, total N2O emissions from (U + NIs) were approximately 29% compared to that from U alone and 36% compared to that from (U + UI), indicating that indirect N2O emission from NH3 induced by NIs may be negligible.

Nitrous oxide (N2O) is an important greenhouse gas which contributes to climate change and ozone depletion. Mineral N fertilizers are one of the most important sources of N2O emission in agricultural systems. Enhanced-efficiency fertilizers (e.g., N fertilizers with added urease and nitrification inhibitors) represent possible approaches to N2O emission reduction and improved efficiency of N use. However, their adoption has been limited by the uncertainty of their effectiveness across different ecosystems. The present study aims to evaluate the effectiveness of several inhibitors under various environmental conditions. We found some of them showed their ability to reduce N2O emissions, for example Piadin and NBPT under laboratory conditions, while some of them are inefficient (NZONE MAX), and some exhibit inconsistent mitigation in N2O emissions (for example DMPP and NBPT under the wheat- wheat- oilseed rape rotation system). Although the nitrification inhibitor Piadin reduced N2O emissions from soil, it also increased the risk of higher NH3 volatilization. Our results reveal the complexity of soil microbial activity in relation to nitrification and denitrification, and provide some references to improve the efficiency of urease and nitrification inhibitors. These inconsistencies in effectiveness highlights the gap between laboratory and field conditions. One of the most important differences is that incubation experiments do not usually include plants. Our third experiment included both unplanted and planted soils. The results confirm our hypothesis that the presence of Lolium perenne increases the activity of microorganisms (probably through the release of root exudates) and lowers N2O emission through intense competition for mineral N between plant and soil microorganisms. However, further scientific questions have arisen from the results which require investigation. For example: how do root exudates regulate denitrifying communities, are root exudates stimulating or inhibiting nitrification and denitrification; how do plant species (e. g. leguminous and non-leguminous) affect the microbial communities; and how does the application of urease and nitrification inhibitors root exudates? In recent projects, researchers have discovered several compounds released from plant root exudates which have significant nitrification inhibition capacity. These biological nitrification inhibitors may provide an effective method of increasing the efficiency of N use and reducing N2O emission in future agricultural systems.

Soil treatments have a significant influence on the agricultural and environmental productivity of agricultural practices. Arable lands are one of the sources of greenhouse gas emissions (GHG) that are influenced by the chemical and physical properties of the soil and are an essential contributor to climate change. We aim to evaluate the long-term management of agricultural practices, such as different tillage systems, cover crops, and glyphosate, on GHG emissions and soil physical properties. The field trial involved three tillage systems (conventional tillage (CT), reduced tillage (RT), and no-tillage (NT)), along with variations in cover cropping (with and without cover crops) and glyphosate application (with and without glyphosate). These treatments were implemented during the cultivation of oilseed rape in 2022 as part of a cropping sequence consisting of five crops: winter wheat; winter oilseed rape; spring wheat; spring barley; and field pea. Greenhouse gas emissions (carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)) were directly measured using a closed static chamber system. Through the examination of these management techniques, the soil’s physical properties over the studied period were assessed for their impact on GHG fluxes. The findings of the study reveal that N2O emissions were relatively low during the first month of measurement, with significant differences (p < 0.05) observed in the interaction between cover crop and glyphosate treatments. Additionally, N2O emissions were notably elevated in the reduced (0.079 µg m−2 h−1) and conventional tillage (0.097 µg m−2 h−1) treatments at the second month of measurement. Regarding CH4, increased emissions were observed in the reduced tillage and cover crop treatments. CO2 emissions exhibited variability across all of the investigated treatments. Notably, GHG fluxes spiked at the second measurement, signifying the maximum uptake of nutrients by the main plants during the growth phase. Greenhouse gas emissions leveled off across all of the treatments following the harvest, marking the end of the cultivation period. The influence of the deployed techniques varied across the determined physical parameters of the soil. The incorporation of cover crops contributed to improved water content and, further, to electrical conductivity. Glyphosate use showed no direct impact on physical properties of the soil while the different tillage treatments had varying effects on the distribution of the physical properties of the soil with respect to the degree of disturbance or tillage-induced changes. Additionally, GHG emissions were strongly correlated with precipitation at one week and two weeks before sampling, except for CO2, which showed a weaker correlation at two weeks before GHG sampling. The findings indicate that reduced and conventional tillage methods might adversely affect greenhouse gas emissions and plant functionality, particularly concerning nutrient release and uptake, especially in temperate climate conditions.

We examined the effects of biochar and urease inhibitors/nitrification inhibitors on nitrification process, ammonia and N2O emission in subtropical soil, and determined the best combination of biochar with nitrification and urease inhibitors. This work could provide a theoretical basis for the mitigation of the negative environmental risk caused by reactive nitrogen gas in the application of nitrogen fertilizer. A indoor aerobic culture test was conducted with seven treatments [urea+biochar (NB), urea+nitrification inhibitor (N+NI), urea+urease inhibitor (N+UI), urea+nitrification inhibitor+urease inhibitor (N+NIUI), urea+nitrification inhibitor+biochar (NB+NI), urea+urease inhibitor+biochar (NB+UI), urea+nitrification inhibitor+urease inhibitor+biochar (NB+NIUI)] and urea (N) as the control. The dynamics of soil inorganic nitrogen content, N2O emission and the volatility of ammonia volatilization were observed under combined application of biochar with urease inhibitor (NBPT)/nitrification inhibitor (DMPP). The results showed that:1)Compared to the control (5.11 mg N·kg-1·d-1) during the incubation period, NB treatment significantly increased therate constant of nitrification by 33.9%, and N+NI treatment significantly reduced the nitrification rate constant by 22.9%. NB treatment significantly increased the abundance of ammonia oxidizing bacteria (AOB) by 56.0%. 2) Compared with N treatment, N+NI and NB+NI treatments signi-ficantly enhanced the cumulative emission of NH3 by 49%. The N+UI treatment reduced the cumulative loss of NH3. The inhibition effect of NB+UI treatment was more significant. 3) The emission rate of N2O was highest in the first 10 days after fertilization. The N2O emission under NB treatment was the earliest, and that of N treatment was the highest (5.87 μg·kg-1·h-1). The combined application of DMPP and NBPT performed the best in reducing soil N2O emission. We estimated global warming potential (GWP) of the direct N2O and indirect N2O (NH3) emissions. Compared with N treatments, N+NI and NB+NI treatments increased the GWP by 34.8% and 40.9%, respectively. While the NB and NB+UI treatments significantly reduced the GWP by 45.9% and 60.5%, the combination of biochar and urease inhibitor had the best effect on reduction of GWP of soil active nitrogen emissions.