Use of a novel nitrification inhibitor to reduce nitrous oxide emission from (15)N-labelled dairy slurry injected into soil

Microbial nitrogen transformations tracked by natural abundance isotope studies and microbiological methods: A review

Nitrogen is an essential nutrient in the environment that exists in multiple oxidation states in nature. Numerous microbial processes are involved in its transformation. Knowledge about very complex N cycling has been growing rapidly in recent years, with new information about associated isotope effects and about the microbes involved in particular processes. Furthermore, molecular methods that are able to detect and quantify particular processes are being developed, applied and combined with other analytical approaches, which opens up new opportunities to enhance understanding of nitrogen transformation pathways. This review presents a summary of the microbial nitrogen transformation, including the respective isotope effects of nitrogen and oxygen on different nitrogen-bearing compounds (including nitrates, nitrites, ammonia and nitrous oxide), and the microbiological characteristics of these processes. It is supplemented by an overview of molecular methods applied for detecting and quantifying the activity of particular enzymes involved in N transformation pathways. This summary should help in the planning and interpretation of complex research studies applying isotope analyses of different N compounds and combining microbiological and isotopic methods in tracking complex N cycling, and in the integration of these results in modelling approaches.

Tracing nitrogen transformations during spring development of winter wheat induced by 15N labeled cattle slurry applied with different techniques

Slurry application is often associated with considerable nitrogen (N) losses: ammonia (NH₃), nitrous oxide (N₂O) and a mostly unknown contribution of dinitrogen (N₂) emission, as well as N leaching. Thus, an outdoor lysimeter experiment with growing winter wheat in undisturbed soil cores was set up to follow the transformation of cattle slurry ¹⁵NH₄⁺ and soil ¹⁵NO₃^- using a double labeling approach. Slurry treatments included the following application techniques: a trailing hose with/without acidification, and open slot injection with/without nitrification inhibitor. The fertilizer application rate was 67 kg N ha^-1. In addition to NH₃ emissions, N₂O and N₂ emissions were measured, as well as N contents and ¹⁵N enrichment of soil N pools and plant compartments. The major gaseous loss pathway was NH₃ with up to 8 kg N ha^-1 following trailing hose application, while slot injection significantly reduced NH₃-N losses. Regardless of the application technique, N₂O emissions were low (up to 0.1 kg N₂O-N ha^-1), while N₂ emissions reached up to 3 kg N ha^-1. No effect on N leaching from topsoil was found. ¹⁵N plant uptake was greater in slot injection than trailing hose treatments. An effect of the nitrification inhibitor was visible in the nitrate contents, but not in gaseous N losses or N leaching from topsoil. Impacts of the application techniques on individual soil N pools were small. The ¹⁵N recovery offered a chance to map the short-term effects and was highest in the soil N_t pool (32 % to 48 % of ¹⁵N applied) with a greater contribution of microbial N than mineral N at beginning of stem elongation. Indications for high N immobilization was derived from the applied N balance approach. In the present case, slot injection scored as the best application technology based on the highest NH₃ reduction, while N₂ and N₂O emissions were not enhanced.

Effect of nitrification inhibitor (DMPP) on nitrous oxide emissions from agricultural fields: Automated and manual measurements

Nitrogen fertilisation contributes significantly to the atmospheric increase of nitrous oxide (N₂O). Application of nitrification inhibitors (NIs) is a promising strategy to mitigate N₂O emissions and improve N-use efficiency in agricultural systems. This study investigated the effect of NI, 3,4-dimethylpyrazol phosphate (DMPP) on N₂O mitigation from spring barley and spring oilseed rape. Manual and automatic chamber methodologies were used to capture spatial and temporal variability in N₂O emissions. In a second experiment, we study the effect of N fertiliser levels without NI (0 %, 50 %, 100 %, 150 % and 200 % of recommended amount of N fertiliser), as well as 100 % of N with NI on N₂O emissions in spring barley. The automated chamber measurements showed dynamics of N₂O changes throughout the season, including positive and negative peaks that were unobservable with manual chambers due to low temporal resolution. Although not significant, application of NI tended to reduce N₂O emissions. The reduction was on average 16 % in spring barley and 58 % in spring oilseed rape in manual chamber measurements. However, N₂O reduction was 108 % in continuous automatic chamber measurements in spring barley. The N₂O EFs for the growing season were very low (0.025 % to 0.148 %), with a greater reduction in EF in spring oilseed rape (76 %) than in spring barley (32 %) with NI application. A positive correlation (R = 80 %) was observed between N fertiliser levels and N₂O emissions. Crop yield and crop N uptake were not significantly affected by the use of NI. This study highlighted that NI can reduce N₂O emissions, but the reduction effects are plot, crop and microclimate specific. Long-term experiments with continuous plot-scale measurements are needed to capture and optimise N₂O mitigation effect of NIs across wide variability in soils and microclimates in agroecosystems.

Management and implications of using nitrification inhibitors to reduce nitrous oxide emissions from urine patches on grazed pasture soils - A review

Livestock urine patches are the main source of nitrous oxide (N₂O) emissions in pastoral system, and nitrification inhibitors (NIs) have been widely investigated as a N₂O mitigation strategy. This study reviews the current understanding of the effect of NIs use on N₂O emissions from urine patches, including the factors that affect their efficacy, as well as the unintended consequences of NIs use. It brings together the fundamental aspects of targeted management of urine patches for reducing N₂O emissions involving inhibitors. The available literature of 196 datasets indicates that dicyandiamide (DCD), 3,4-dimethylpyrazole phosphate (DMPP), and 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin) reduced N₂O emissions from urine patches by 44 ± 2%, 28 ± 38% and 28 ± 5%, (average ± s.e.), respectively. DCD also increased pasture dry matter and nitrogen (N) uptake by 13 ± 2% and 15 ± 3%, (average ± s.e.), respectively. The effect of DMPP and nitrapyrin on pasture dry matter and N uptake, assessed in only one study, was not significant. It also suggests that harmonizing the timing of inhibitor use with urine-N transformation increase the efficacy of NIs. No negative impacts on non-targeted soil and aquatic organisms have been reported with the recommended rate of DCD applied to urine and recommended applications of DMPP and nitrapyrin for treated mineral fertilisers and manures. However, there was evidence of the presence of small amounts of DCD residues in milk products as a result of its use on livestock grazed pasture. DMPP and nitrapyrin can also enter the food chain via grazing livestock. The study concludes that for the use of NIs in livestock grazed systems, research is needed to establish acceptable maximum residue level (MRL) of NIs in soil, plant, and animal products, and develop technologies that optimise physical mixing between NIs and urine patches.

Comparative Effectiveness of Four Nitrification Inhibitors for Mitigating Carbon Dioxide and Nitrous Oxide Emissions from Three Different Textured Soils

Nitrification inhibitors (NIs) can be used to reduce both NO3−-N leaching and N2O-N emissions. However, the comparative efficacies of NIs can be strongly affected by soil type. Therefore, the efficacies of four nitrification inhibitors (dicyandiamide (DCD), 3, 4-dimethylpyrazole phosphate (DMPP), nitrogenous mineral fertilizers containing the DMPP ammonium stabilizer (ENTEC) and active ingredients: 3.00–3.25% 1, 2, 4-triazole and 1.50–1.65% 3-methylpyrazole (PIADIN)) were investigated in three different textured N-fertilized (0.5 g NH4+-N kg−1 soil) soils of Schleswig-Holstein, namely, Marsch (clayey), Östliches Hügelland (loamy) and Geest (sandy) under a controlled environment. Total CO2-C and N2O-N emissions were significantly higher from Marsch than Östliches Hügelland and Geest. In Marsch, DMPP showed the highest inhibitory effect on CO2-C emission (50%), followed by PIADIN (32%) and ENTEC (16%). In Östliches Hügelland, DCD and PIADIN showed the highest and equal inhibitory effect on CO2-C emission (73%), followed by DMPP (64%) and ENTEC (36%). In Marsch and Östliches Hügelland, DCD showed the stronger inhibitory effect on N2O-N emission (86% and 47%) than DMPP (56% and 30%) and PIADIN (54% and 16%). In Geest, DMPP was more effective in reducing N2O-N emission (88%) than PIADIN (70%) and DCD (33%). Thus, it can be concluded that DCD is a better NI for clay and loamy soils, while DMPP and PIADIN are better for sandy soils to inhibit soil nitrification and gaseous emissions.

Field Application of Organic Fertilizers Triggers N2O Emissions From the Soil N Pool as Indicated by 15N-Labeled Digestates

Anaerobic digestion (AD) can generate biogas while simultaneously producing digestate which can be used as fertilizer. Feedstocks used for AD influence digestate composition, which in turn may affect carbon (C) and nitrogen (N) turn-over in soils and subsequently influence nitrous oxide (N2O) emissions after soil application. Assessment of greenhouse gas emissions from digestates can help to evaluate the overall sustainability of an agricultural production system. The objective of this study was therefore to evaluate and understand the effect of differences in digestate composition on in situ N2O emissions within the 1st weeks after application of seven digestates. The digestates were derived from different feedstocks and 15N-labeled, either in total N or only in ammonium-N. Therefore, the experimental design enabled us to differentiate between potential N2O-N sources (i.e., digestate N or soil N). Furthermore, it allowed to distinguish to some extent between organic-N and ammonium-N as potential N sources for denitrification. Digestates were homogeneously incorporated into the upper 5 cm of microplots in an arable Haplic Luvisol in South Germany at a rate of 170 kg N ha−1. After application, N2O fluxes were measured for ~60 days (May-July) using the closed chamber method in 2 experimental years. Mainly due to higher precipitations in the 1st year, cumulative N2O emissions were higher (312–1,580 g N2O-N ha−1) compared to the emissions (133–690 g N2O-N ha−1) in the 2nd year. Between 16–33% (1st year) and 17–38% (2nd year) of N2O emissions originated from digestate N, indicating that digestate application triggered N2O production and release mainly from soil N. This effect was strongest immediately after digestate application. It was concluded that the first (short term) peak in N2O emissions after digestate application is largely related to denitrification of soil-N. However, the experimental setup does not allow to differentiate between the different denitrification pathways. Weather conditions showed a substantial effect on N2O emissions, where the correlation between N2O and CO2 flux rates hinted on denitrification as main N2O source. The effect of digestate composition, particularly organic N from the digestate, on soil N2O emissions seems to be of minor relevance.

Effect of Nitrification Inhibitors on N2O Emissions after Cattle Slurry Application

Cattle slurry injection (INJ) has shown to be an efficient measure to reduce ammonia (NH3) losses from soils but it might also significantly increase nitrous oxide (N2O) emissions, which can dominate the total greenhouse gas (GHG) release in silage maize production (Zea mays L.). Nitrification inhibitors (NIs) are known for their potential to mitigate N2O. Therefore, we tested the effect of NIs added to cattle slurry before INJ on N2O fluxes from a Haplic Luvisol under silage maize in southwest Germany. We determined N2O fluxes at least weekly, with the closed chamber method over two full years. NIs differ in their chemical and physical behavior and we therefore tested a range of commercially available NIs: 3,4-dimethylpyrazole phosphate, 3,4-dimethylpyrazol succinic acid, a mixture of both, nitrapyrin, dicyandiamide, and 1,2,4 triazol and 3-methylpyrazol. Although not significant, INJ treatments with NI showed lower mean annual N2O emissions than the INJ treatment without NI in the 1st year. The emission reduction by NI of 46% in the 2nd year was statistically significant. In both years, we did not find any difference in N2O release, crop yield, or nitrogen removal between the different NI treatments. In the 1st year, which was extraordinary dry and warm, emission factors (EFs) for all INJ treatments were 4 to 8-fold higher than default EF from the IPCC. Even in the 2nd year, only three NI treatments reached EFs within the range provided by the IPCC. Direct N2O accounted for between 81 and 91% of the total GHG emission. Area- and yield-related GHG emission of the broadcast application with subsequent incorporation was in both years in the statistical class with lowest emission. In contrast, INJ with NIs showed similar GHG emissions in only one year, and consequently, incorporation was found to be the optimum management practice for livestock farmers in our study region.

The Nitrification Inhibitor Vizura® Reduces N2O Emissions When Added to Digestate before Injection under Irrigated Maize in the Po Valley (Northern Italy)

The agricultural area in the Po Valley is prone to high nitrous oxide (N2O) emissions as it is characterized by irrigated maize-based cropping systems, high amounts of nitrogen supplied, and elevated air temperature in summer. Here, two monitoring campaigns were carried out in maize fertilized with raw digestate in a randomized block design in 2016 and 2017 to test the effectiveness of the 3, 4 DMPP inhibitor Vizura® on reducing N2O-N emissions. Digestate was injected into 0.15 m soil depth at side-dressing (2016) and before sowing (2017). Non-steady state chambers were used to collect N2O-N air samples under zero N fertilization (N0), digestate (D), and digestate + Vizura® (V). Overall, emissions were significantly higher in the D treatment than in the V treatment in both 2016 and 2017. The emission factor (EF, %) of V was two and four times lower than the EF in D in 2016 and 2017, respectively. Peaks of NO3-N generally resulted in N2O-N emissions peaks, especially during rainfall or irrigation events. The water-filled pore space (WFPS, %) did not differ between treatments and was generally below 60%, suggesting that N2O-N emissions were mainly due to nitrification rather than denitrification.

Effects of the Nitrification Inhibitor 3,4-Dimethylpyrazole Phosphate on Nitrification and Nitrifiers in Two Contrasting Agricultural Soils

The nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) is a powerful tool that can be used to promote nitrogen (N) use efficiency and reduce N losses from agricultural systems by slowing nitrification. Mounting evidence has confirmed the functional importance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in nitrification and N2O production; however, their responses to DMPP amendment and the microbial mechanisms underlying the variable efficiencies of DMPP across different soils remain largely unknown. Here we compared the impacts of DMPP on nitrification and the dynamics of ammonia oxidizers between an acidic pasture soil and an alkaline vegetable soil using a (15)N tracing and (13)CO2-DNA-stable-isotope probing (SIP) technique. The results showed that DMPP significantly inhibited nitrification and N2O production in the vegetable soil only, and the transient inhibition was coupled with a significant decrease in AOB abundance. No significant effects on the community structure of ammonia oxidizers or the abundances of total bacteria and denitrifiers were observed in either soil. The (15)N tracing experiment revealed that autotrophic nitrification was the predominant form of nitrification in both soils. The (13)CO2-DNA-SIP results indicated the involvement of AOB in active nitrification in both soils, but DMPP inhibited the assimilation of (13)CO2 into AOB only in the vegetable soil. Our findings provide evidence that DMPP could effectively inhibit nitrification through impeding the abundance and metabolic activity of AOB in the alkaline vegetable soil but not in the acidic pasture soil, possibly due to the low AOB abundance or the adsorption of DMPP by organic matter.

IMPORTANCE

The combination of the (15)N tracing model and (13)CO2-DNA-SIP technique provides important evidence that the nitrification inhibitor DMPP could effectively inhibit nitrification and nitrous oxide emission in an alkaline soil through influencing the abundance and metabolic activity of AOB. In contrast, DMPP amendment has no significant effect on nitrification or nitrifiers in an acidic soil, potentially owing to the low abundance of AOB and the possible adsorption of DMPP by organic matter. Our findings have direct implications for improved agricultural practices through utilizing the nitrification inhibitor DMPP in appropriate situations, and they emphasize the importance of microbial communities to the efficacy of DMPP.

Role of organic amendment application on greenhouse gas emission from soil

Globally, substantial quantities of organic amendments (OAs) such as plant residues (3.8×10(9) Mg/yr), biosolids (10×10(7) Mg/yr), and animal manures (7×10(9) Mg/yr) are produced. Recycling these OAs in agriculture possesses several advantages such as improving plant growth, yield, soil carbon content, and microbial biomass and activity. Nevertheless, OA applications hold some disadvantages such as nutrient eutrophication and greenhouse gas (GHG) emission. Agriculture sector plays a vital role in GHG emission (carbon dioxide- CO2, methane- CH4, and nitrous oxide- N2O). Though CH4 and N2O are emitted in less quantity than CO2, they are 21 and 310 times more powerful in global warming potential, respectively. Although there have been reviews on the role of mineral fertilizer application on GHG emission, there has been no comprehensive review on the effect of OA application on GHG emission in agricultural soils. The review starts with the quantification of various OAs used in agriculture that include manures, biosolids, and crop residues along with their role in improving soil health. Then, it discusses four major OA induced-GHG emission processes (i.e., priming effect, methanogenesis, nitrification, and denitrification) by highlighting the impact of OA application on GHG emission from soil. For example, globally 10×10(7) Mg biosolids are produced annually which can result in the potential emission of 530 Gg of CH4 and 60 Gg of N2O. The article then aims to highlight the soil, climatic, and OA factors affecting OA induced-GHG emission and the management practices to mitigate the emission. This review emphasizes the future research needs in relation to nitrogen and carbon dynamics in soil to broaden the use of OAs in agriculture to maintain soil health with minimum impact on GHG emission from agriculture.

Subsurface application of manures slurries for conservation tillage and pasture soils and their impact on the nitrogen balance

Injection of cattle and swine slurries can provide soil incorporation in no-till and perennial forage production. Injection is expected to substantially reduce N loss due to ammonia (NH3) volatilization, but a portion of that N conservation may be offset by greater denitrification and leaching losses. This paper reviews our current knowledge of the impacts of subsurface application of cattle and swine slurries on the N balance and outlines areas where a greater understanding is needed. Several publications have shown that liquid manure injection using disk openers, chisels, or tines can be expected to Sreduce NH, emissions by at least 40%, and often by 90% or more, relative to broadcast application. However, the limited number of studies that have also measured denitrification losses have shown that increased denitrification with subsurface application can offset as much as half of the N conserved by reducing NH3 emissions. Because the greenhouse gas nitrous oxide (N2O) is one product of denitrification, the possible increases in N2O emission with injection require further consideration. Subsurface manure application generally does not appear to increase leaching potential when manure is applied at recommended rates. Plant utilization of conserved N was shown in only a portion of the published studies, indicating that further work is needed to better synchronize manure N availability and crop uptake. At this time in the United States, the economic and environmental benefits from reducing losses of N as NH3 are expected to outweigh potential liability from increases in denitrification with subsurface manure application. To fully evaluate the trade-offs among manure application methods, a detailed environmental and agricultural economic assessment is needed to estimate the true costs of potential increases in NO2O emissions with manure injection.

Effect of cattle slurry pre-treatment by separation and addition of nitrification inhibitors on gaseous emissions and N dynamics: a laboratory study

The application of untreated or treated animal manure to soils can result in increased N and C gaseous emissions contributing to ecosystem change and global warming. In the present study, dairy cattle slurry (liquid manure) was subjected first to pre-treatment by separation using a screw press to obtain a liquid (LF) and a solid fraction (SF). Then, the different fractions and the whole slurry (WS) were combined with two nitrification inhibitors (NI), dicyandiamide (DCD) or 3,4-dimethylpyrazole phosphate (DMPP), were applied to soil to assess the effect of slurry treatment by separation and NI addition on soil N dynamics and CH4, CO2, NH3, NO and N2O emissions. The WS and the two slurry fractions, combined or not with DCD or DMPP, were applied to soil at an equivalent field dosage of 120 kg total N ha(-1). Controls including a soil only, soil-DCD and soil-DMPP treatments were also included. The mixtures were incubated for 93-d at 20 degrees C. Results obtained show that NI inhibited nitrification between 16 and 30-d in WS and LF, with DMPP having a longer effect over time compared to DCD. There was no significant effect of NI on nitrification for the SF treatment. Nitrification inhibitors did not significantly affect (P>0.05) the CH4, CO2 and N2O emissions, but significantly decreased (P<0.05) NO emissions. Furthermore, the two NIs had a similar effect on gaseous emissions. Throughout the entire experiment, the greatest amount of NO was released from the LF treatment (without NI), while the greatest amount of N2O was released from the SF treatment. Slurry separation had no impact on N emissions, while the combination of this process with one of the two NI led to a small reduction in total N emissions.