Search

This document is a letter to the editor in response to an article titled "An examination of the ability of plantain (Plantago lanceolata L.) to mitigate nitrogen leaching from pasture systems." The authors of the letter express their disagreement with certain aspects of the article, specifically regarding the role of dairy cow urinary nitrogen in leaching from pasture systems. They argue that urine is a major source of nitrate leaching and cite previous studies to support their claim. They also criticize the article for focusing on a specific rate of nitrogen in urine patches, which they believe is not widely used in policy or reputable models. The authors conclude that the article's conclusions are confusing and unhelpful for understanding the role of urinary nitrogen in New Zealand's water quality challenges. [Extracted from the article]

As global efforts to combat climate change intensify, agricultural emissions are increasingly scrutinized. Biogas slurry (BS), a by-product of agricultural waste, not only provides essential nutrients for crops but can also elevate soil nitrous oxide (N2O) emissions. This study investigates the immediate and long-term impacts of BS application on N2O emissions, taking into account the frequency of application and evaluating the effectiveness of nitrification inhibitor 3,4-dimethylpyrazole-phosphate (DMPP) in reducing emissions. Through a microcosm incubation experiment with a 108 h robotized incubation-monitoring system, it was found that N2O emissions spiked immediately following a single BS application, with emissions decreasing within 30 days. Repeated BS applications yielded lower cumulative emissions. Elevated N2O emissions were linked to higher soil pH and ammonium (NH4+) levels, along with reduced nitrate (NO3−) concentrations after a single BS application. The combined application of BS and DMPP proved most effective in inhibiting nitrification and cumulative N2O emissions, achieving reductions of 63.0% and 94.6%, respectively. High soil pH, NH4+, and low NO3− were identified as pivotal factors in this effect. These findings highlight the need for mitigation strategies such as dilution or splitting applications to reduce emissions. Integrating BS with DMPP offers a sustainable approach to achieving both agricultural and environmental goals. [ABSTRACT FROM AUTHOR]

Enhancing fertilizer nitrogen use efficiency (NUE) in corn (Zea mays L.) production is critical for closing yield gaps, increasing producer profitability, and promoting environmental stewardship. In 2014 and 2015, a field experiment was conducted to determine the potential for fertilizer N stabilizer products to improve NUE of granular urea and urea ammonium nitrate (UAN) solution applied to strip‐till corn. A urease inhibitor (UI) or nitrification inhibitor (NI) or both were added at labeled rates to urea or UAN solution for a target rate of 180 kg N ha−1. At V3, a single application of broadcast granular urea and subsurface banded UAN solution with and without fertilizer N stabilizers was made. A split application (50% at V3; 50% at V6) of subsurface banded UAN solution served as a control representing a standard grower practice. Fertilizer N stabilizers improved components of NUE, such as grain N recovery efficiency (GNRE) and partial factor productivity (PFP). A single full rate UAN application did not differ in terms of grain yield each year but did result in less PFP and GNRE in 2015 as compared to the grower standard practice. A timely one‐time full season N rate subsurface banded application of UAN treated with UI and NI to improve NUE could be a viable substitute for the practice of multiple fertilizations. Untreated broadcast urea was inferior to UAN as a N source for corn, but when treated with both a UI and NI, NUE was improved. [ABSTRACT FROM AUTHOR]

Nitrification inhibitors, such as nitrapyrin (NI), are increasingly co‐applied with nitrogen (N) fertilizers as part of sustainable agricultural practice. Several studies in temperate regions have documented the effectiveness of NI in retaining soil ammonium (NH4+), minimizing N loss and increasing crop yields. However, less is known about the effects of NI in Mediterranean regions, where agricultural production is challenging and requires intensive irrigation and fertilization. We investigated the short‐term impact of the nitrification inhibitor nitrapyrin (2‐chloro‐6‐(trichloromethyl)pyridine) in a two‐factor mesocosm experiment, using a typical Mediterranean soil, where NI was co‐applied with a selection of urea‐based fertilizers: urea (U), U with urease inhibitors (U + UI), methylene urea (MU) and zeolite‐coated urea (ZU). NI co‐applied with urea fertilizers resulted in higher availability of soil NH4+ and a concurrent increase in NH3 volatilization. Net cumulative soil NH4+ availability was 1.5–3.3 fold greater when NI was applied. Concurrently, net cumulative nitrate (NO3−) and nitrite (NO2−) availability was reduced by 10%–60%; this was found for all the tested fertilizer types except MU fertilizer, where the net cumulative soil NO3− and NO2− doubled. Nitrous oxide (N2O) emissions from urea fertilization were reduced by 40% with UI, 50% with NI and 66% with NI + UI. Interestingly, after 28 d, the composition of soil microbial communities was distinctly different, due to NI application. Specifically, NI application dramatically reduced the abundance of ammonia‐oxidizing and denitrifying bacterial functional groups. NI was effective in reducing N2O emissions in this calcareous soil; however, NH3 emissions were remarkably enhanced. These findings have important implications for the large‐scale adoption of inhibitor technologies in Mediterranean agroecosystems and for the reduction of greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

To meet the growing population's demand for food, humans have introduced large amounts of nitrogen fertilizers into agricultural systems, resulting in highly nitrified environments in most farmland soils. In highly nitrified environments, the application of nitrogen fertilizer easily leads to the formation of nitrate (NO3−) and subsequent leaching, resulting in very low utilization rates. Moreover, nitrogen loss can cause harm to both the environment and human health, making it necessary to inhibit the nitrification process. Nitrification inhibitors can suppress nitrification, and inhibitors derived biologically from plant roots are gaining attention due to their low cost and environmental friendliness. Sorghum, as a crop capable of growing in arid environments, holds economic value and also possesses the ability to secrete biological nitrification inhibitors. This article utilizes sorghum as a case study to review different types of BNIs (MHPP, sorgoleone, and sakuranetin), their mechanisms of inhibition, and influencing factors. This article summarizes the contributions of these inhibitors in reducing N2O emissions and increasing food production, while also providing insight into future research directions for sorghum's biological nitrification inhibitors in terms of agricultural production efficiency. BNIs are expected to play an important role in improving agricultural production and reducing environmental pollution. [ABSTRACT FROM AUTHOR]

Ammonium sulfate (AS) has been utilized in agriculture; however, there is a dearth of research on its application in maize cultivation subsequent to the implementation of nitrification inhibitors or coating treatments. This study aimed to analyze the impacts of various combinations of AS fertilizers on soil nutrients, plant nutrient uptake, yield, and fertilizer utilization efficiency in maize cultivation to establish an optimal and stabilized disposal method for AS. A completely randomized design was employed with five treatments (AU, the control using urea; AS, treatment using ammonium sulfate; ASN, treatment using ammonium sulfate with a nitrification inhibitor; ASG, treatment using oil-coated ammonium sulfate; and ASD, treatment using oil–humic acid-coated ammonium sulfate). The results show the following: (1) Compared with AU and AS, ASN, ASG, and ASD decreased the leaching rates of total nitrogen (TN), ammonium nitrogen (NH4+-N), and nitrate nitrogen (NO3−-N), and more residual N had accumulated in the soil. The first-order kinetic equation Nt = N0(1 − e−kt) could better fit the process of N accumulation and release, and the N-release rate constant was in the order of AU > CK > AS > ASG > ASN > ASD. (2) Compared with the AU and AS treatments, the plant dry weight, grain dry weight, spike width, spike length, and yields of maize increased by 8.85–11.08%, 12.98–14.15%, 2.95–3.52%, 5.50–5.65%, and 43.21–51.10%, respectively, under the ASG treatment. A path analysis revealed the main decision coefficient of the effective spike number on the maize yield. Furthermore, the accumulation levels of N, P, and K within above-ground plants significantly increased under the ASG treatment compared with those under the AU and AS treatments. N, P, and K partial factor productivity under the ASG treatment increased by 47.12%, 47.15%, and 73.40% on average, while grain N, P, and K balance increased by 50.45%, 47.10%, 55.61% on average, compared with the AU and AS treatments. Therefore, the ASG treatment exhibited the optimal slow-release effect on nutrients and achieved excellent performance in enhancing the production and efficiency of maize. [ABSTRACT FROM AUTHOR]

Ammonia loss following nitrogen fertilization can degrade air quality and impact human health, whereas nitrous oxide (N2O) can contribute to global warming and climate change. Mitigation practices that target only one N‐loss pathway can lead to pollution swamping; hence, practices targeting both N‐losses are required. A 3‐year field study examined fertilizer N‐placement (broadcast urea, single‐slot injection of urea ammonium nitrate [UAN], double‐slot UAN injection) and N‐metabolization inhibitors (with/without urease and nitrification inhibitors) impacts on NH3 and N2O losses and corn yields. Ammonia volatilization was reduced (p < 0.05) by 26% with single‐slot UAN injection (10.6 kg N ha−1) and by 63% with double‐slot UAN injection (5.32 kg N ha−1) compared to broadcast urea (14.3 kg N ha−1). Dual urease and nitrification inhibitors reduced NH3 volatilization (0.84–3.86 kg N ha−1) by 57%–92% compared to no inhibitors (5.32–14.3 kg N ha−1). When no inhibitors were applied, N2O emissions from slot injection (6.43–7.62 kg N ha−1) were 2.6–3.1 times greater than from broadcast urea (2.43 kg N ha−1). Dual inhibitors reduced N2O emissions by 43% from 6.43 to 3.66 kg N ha−1 with double‐slot injection. Double‐slot UAN injection increased corn grain yields (9.73 t ha−1) by 12%–13% compared to single‐slot UAN injection (8.71 t ha−1) and broadcast urea (8.6 t ha−1). Double‐slot UAN injection effectively decreased NH3 losses and increased corn grain yields, but dual N inhibitors were required to also reduce N2O. Hence, combined productivity and environmental benefits were accrued only when fertilizer containing urease and nitrification inhibitors was combined with double‐slot injection. Core Ideas: Single‐slot and double‐slot UAN injection reduced NH3 loss by 26% and 63%, respectively, compared to broadcast urea.Dual inhibitors with broadcast urea or UAN injection reduced NH3 losses by 57%–92% compared to no inhibitors.Dual inhibitors reduced N2O emissions by 18% with single‐slot injection and by 43% with double‐slot injection.Double‐slot injection increased corn grain yields by 12%–13% compared to broadcast urea and single‐slot injection.Double‐slot injection with dual inhibitors increased yields and resulted in dramatic decreases in NH3 and N2O. [ABSTRACT FROM AUTHOR]

Purpose: To clarify the effects of maize straw retention combined with reduced fertilization and urease/nitrification inhibitors on the accumulation and leaching potential of mineral N in the deep soil profile of no-tillage agroecosystem. Methods: A 15N-tracing micro-plot experiment was conducted with four treatments (NPK, traditional NPK fertilization; NPKS, NPK with maize straw retention; RNPKS, NPKS with 20% fertilizer-N reduction; and RNPKSI, RNPKS with inhibitors application) in the Mollisol of Northeast China. We analyzed fertilizer-N transformation dynamics in different soil N pools, quantified the fertilizer N use efficiency in crops, and evaluated fertilizer-derived nitrate leaching losses throughout the complete maize growing period. Results: Our analyses revealed that, compared to the NPK treatment, NPKS, RNPKS, and RNPKSI remarkably reduced the accumulation of urea-derived mineral-N during maize seedling stage by enhancing the transformation of urea-N into fixed NH4+-N and organic-N pools, both of which could be quickly released for maize uptake following the extension of crop growth periods. At the maize ripening stage, soil NO3−-N and 15N-labeled urea-derived NO3−-N, which migrated vertically to a depth of 80–100 cm, were significantly reduced by treatments of RNPKS and RNPKSI without minimizing crop yields when compared with NPK. Conclusion: Our results suggest that combining maize straw retention with reduced fertilization and the application of urease/nitrification inhibitors can be efficient management practices for lowering urea N leaching risk, improving N use efficiency, and maintaining or even increasing crop yields by enhancing soil N retention and supply in the croplands of Northeast China. [ABSTRACT FROM AUTHOR]

Climate change has been intensifying soil drying and rewetting cycles, which can alter the soil microbiome structure and activity. Here we hypothesized that a soil drying-rewetting cycle enhances biodegradation and, hence, decreases the effectiveness of nitrification inhibitors (NIs). The effectiveness of DMPP (3,4-Dimethylpyrazole phosphate) and MP + TZ (3-Methylpyrazol and Triazol) was evaluated in 60-day incubation studies under a drying and rewetting cycle relative to constant low and high soil moisture conditions (40% and 80% water-holding capacity, WHC, respectively) in two different textured soils. The measurements included (i) daily and cumulative N2O-N emissions, (ii) soil NH4+-N and NO3−-N concentrations, and (iii) the composition of bacterial soil communities. Application of DMPP and MP + TZ reduced the overall N2O-N emissions under drying-rewetting (-45%), as well as under 40% WHC (-39%) and 80% WHC (-25%). DMPP retarded nitrification and decreased N2O-N release from the sandy and silt loam soils, while MP + TZ mitigated N2O-N production only from the silt loam soil. Unexpectedly, between days 30 and 60, N2O-N emissions from NI-treated soils increased by up to fivefold relative to the No-NI treatment in the silt loam soil at 80% WHC. Likewise, the relative abundance of the studied nitrifying bacteria indicated that the NIs had only short-term effectiveness in the silt loam soil. These results suggested that DMPP and MP + TZ might trigger high N2O-N release from fine-textured soil with constant high moisture after this short-term inhibitory effect. In conclusion, DMPP and MP + TZ effectively reduce N2O-N emissions under soil drying and rewetting. [ABSTRACT FROM AUTHOR]

Processing tomato (Lycopersicon esculentum Mill.) is regarded amongst the most dominant horticultural crops globally. Yet, due to its elevated water and fertilization needs, its environmental footprint is significantly high. The recent efforts to reduce the footprint of agriculture have rekindled the search for optimized fertilization regimes in tomato. The aim of the present study was to assess the effect of different urea fertilizers and tomato pomace-based composts on the performance and quality traits of processing tomato. A two-year field experiment was conducted in the Larissa region, Central Greece, during 2018–2019. The experiment was set up in a randomized complete block design (RCBD), with five treatments: control, urea (Urea), urea with nitrification and urease inhibitors (Urea + NI + UI), processing tomato pomace with farmyard manure (TP + FM), and processing tomato pomace with compost from plant residues (TP + CM). Measurements included soil total nitrogen (STN), soil organic matter (SOM), root length density (RLD), arbuscular mycorrhiza fungi (AMF) colonization, dry weight per plant, fruit yield (number per plant, total yield, weight, diameter), fruit firmness, total soluble solids (TSS), titratable acidity (TA), lycopene content and yield, and fruit surface color (L*, a*, b*, CI). Overall, the best results in soil properties and quality traits were reported in the organic fertilization treatments (STN, SOM, AMF, TSS, TA, lycopene content, L*, a*, b*) and the differences among TP + FM and TP + CM were insignificant in their majority. On the contrary, fruit yield and its components were significantly improved in Urea + NI + UI. [ABSTRACT FROM AUTHOR]

Agricultural nitrous oxide (N2O) emission reduction strategies are required given the potency of N2O as a greenhouse gas. However, the growing influence of N2O on stratospheric ozone (O3) with declining stratospheric chlorine means the wider atmospheric impact of N2O reductions requires investigation. We calculate a N2O emission reduction of 1.35 TgN2O yr-1 (~5% of 2020 emissions) using spatially separate deployment of nitrification inhibitors ($70–113 tCO2e−1) and crushed basalt (no-cost co-benefit) which also sequesters CO2. In Earth System model simulations for 2025–2075 under high (SSP3-7.0) and low (SSP1-2.6) surface warming scenarios, this N2O mitigation reduces NOx-driven O3 destruction, driving regional stratospheric O3 increases but with minimal impact on total O3 column recovery. By 2075, the radiative forcing of the combined N2O and CO2 reductions equates to a beneficial 9–11 ppm CO2 removal. Our results support targeted agricultural N2O emission reductions for helping nations reach net-zero without hindering O3 recovery. [ABSTRACT FROM AUTHOR]

Up to 70% of the nitrogen (N) fertilizer applied to agricultural soils is lost through microbially mediated processes, such as nitrification. This can be counteracted by synthetic and biological compounds that inhibit nitrification. However, for many biological nitrification inhibitors (BNIs), the interaction with soil properties, nitrifier specificity, and effective concentrations are unclear. Here, we investigated three synthetic nitrification inhibitors (SNIs) (DCD, DMPP, and nitrapyrin) and three BNIs [methyl 3(4-hydroxyphenyl) propionate (MHPP), methyl 3(4-hydroxyphenyl) acrylate (MHPA), and limonene] in two agricultural soils differing in pH and nitrifier communities. The efficacies of SNIs and BNIs were resilient to short-term pH changes in the neutral pH soil, whereas the efficacy of some BNIs increased by neutralizing the alkaline soil. Among the BNIs, MHPA showed the highest inhibition and was, together with MHPP, identified as a putative AOB/comammox-selective inhibitor. Additionally, MHPA and limonene effectively inhibited nitrification at concentrations comparable to those used for DCD. Moreover, we identified the effective concentrations at which 50% and 80% of inhibition is observed (EC50 and EC80) for the BNIs, and similar EC80 values were observed in both soils. Overall, our results show that these BNIs could potentially serve as effective alternatives to SNIs currently used. [ABSTRACT FROM AUTHOR]

The efficacy of various nitrification inhibitors (NIs) relies on their mode of action, their target specificity, and the composition of the soil nitrifying community. Improved inhibition of nitrification requires more targeted and efficient NIs that account for the complex interactions between abiotic parameters and the nitrifying community, including the potential role of ammonia-oxidizing archaea or heterotrophic organisms in nitrification. Increased understanding of these complex interactions can lead to a more rationalized application of NIs and improve their efficacy for sustainable management practices in agroecosystems. Nitrification is a key microbial process in the nitrogen (N) cycle that converts ammonia to nitrate. Excessive nitrification, typically occurring in agroecosystems, has negative environmental impacts, including eutrophication and greenhouse gas emissions. Nitrification inhibitors (NIs) are widely used to manage N in agricultural systems by reducing nitrification rates and improving N use efficiency. However, the effectiveness of NIs can vary depending on the soil conditions, which, in turn, affect the microbial community and the balance between different functional groups of nitrifying microorganisms. Understanding the mechanisms underlying the effectiveness of NIs, and how this is affected by the soil microbial communities or abiotic factors, is crucial for promoting sustainable fertilizer practices. Therefore, this review examines the different types of NIs and how abiotic parameters can influence the nitrifying community, and, therefore, the efficacy of NIs. By discussing the latest research in this field, we provide insights that could facilitate the development of more targeted, efficient, or complementary NIs that improve the application of NIs for sustainable management practices in agroecosystems. [ABSTRACT FROM AUTHOR]

Technologies have been developed for the in-situ treatment of urine patches deposited by grazing livestock to mitigate nitrogen (N) losses using N transformation inhibitors. For this mitigation to be effective, close contact between the applied inhibitors and the N in the urine patch is required (similar to N-fertilisers coated with inhibitors). This research aimed to determine the proportions of urine-N that mixed with inhibitor at or exceeding the threshold concentration (inhibitor concentration at which the nitrification rate is reduced by at least 40%) when inhibitors were applied to simulated urine patches at 4, 24 and 48 h after synthetic urine application. Three commonly used nitrification inhibitors (NIs) [dicyandiamide (DCD), 3,4-dimethylpyrazole phosphate (DMPP), and 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin)] were applied at 40 mL of inhibitor per urine-patch at two different concentrations. The field studies were undertaken in two dairy-grazed pasture soils with contrasting drainage. Large proportions of applied NIs (38%–59% DCD, 27%–58% DMPP, and 31%–58% nitrapyrin) were retained in the pasture canopy. In most cases, the inhibitor threshold concentration was present only within the top 0–20 mm of the soil, with only 16%–40% of the urine-N present. In some cases, the proportions of urine-N intercepted was 12%–15% higher when inhibitors were applied 4 h after urine application compared to delayed application of 24 and 48 h after urine application. Our results revealed that a substantial proportion of N in the urine-patch remained out of the reach of the inhibitor solution. This is possibly due to the small volume (40 mL per 2 L urine patch, 1:50) of the inhibitors applied, with up to 59% of inhibitor solution retained in the pasture canopy. The time delays (4 to 48 h) between the urine deposition and the inhibitor application could have also contributed to this poor physical mixing between inhibitor and urine. Increasing the volume of water applied with the inhibitor and assessing the effect of rainfall/irrigation on increasing urine-N and inhibitor mixing warrants further consideration. [ABSTRACT FROM AUTHOR]

In order to elucidate the effects of nitrification inhibitor dicyandiamide (DCD) on physiological and biochemical characteristics of paddy diazotrophic cyanobacteria and provide a theoretical basis for reasonable application of DCD and diazotrophic cyanobacteria in paddy fields, the variations of growth, photosynthesis, nitrogenase activity, activities of antioxidative enzymes, and oxidative damage characteristics of a paddy diazotrophic cyanobacterium Aliinostoc sp. YYLX235 under DCD stress were investigated. The results showed that the growth of Aliinostoc sp. YYLX235 was inhibited by DCD at concentrations of 100 ~ 300 mg⋅L-1. The activities of cellular vitality and N2-fixation significantly decreased at a DCD concentration of 50 mg⋅L-1. The photosystem II of Aliinostoc sp. YYLX235 exhibited hormetic effects under DCD stress, with characteristics of increasing cellular pigment contents and improvement of electron transfer efficiency. The activities of superoxide dismutase (SOD) and catalase (CAT) in cells of Aliinostoc sp. YYLX235 were positively correlated with DCD concentration in the medium. The oxidative-antioxidative system in cells of Aliinostoc sp. YYLX235 lost balance when DCD concentration ranged from 200 mg⋅L-1 to 300 mg⋅L-1, resulting in oxidative damage to algal cells. The results of this study indicate that DCD has strong negative effects on growth, cellular vitality, and N2-fixation activity of paddy diazotrophic cyanobacteria. Thus, the application of diazotrophic cyanobacteria-based bio-fertilizer and DCD should be staggered. [ABSTRACT FROM AUTHOR]

Nitrification inhibitors are essential in agricultural and environmental production practices. They play a crucial role in promoting agricultural and environmental sustainability by enhancing nitrogen use efficiency, boosting crop yields, and mitigating the adverse environmental effects of nitrogen losses. This bibliometric analysis covers the period from 2004 to 2023, offering a detailed examination of the development of nitrification inhibitor research. The study demonstrates a consistent growth in research publications, indicating sustained interest and dedication to advancing the field. It identifies key contributors, such as institutions and researchers, and underscores the significance of their work through citation analysis. Keyword co-occurrence analysis reveals four distinct clusters focusing on enhancing crop yields, understanding microbial community dynamics, exploring grazing pasture applications, and addressing environmental impact mitigation. The cutting-edge area of keyword burst detection research has transitioned from fundamental research to comprehensive nitrogen management practices. This analysis provides insights into the current research landscape of nitrification inhibitors and proposes future research directions, underscoring the critical role of this field in tackling global agricultural and environmental challenges. [ABSTRACT FROM AUTHOR]

Nitrogen losses of nitrous oxide (N2O) in grazed grassland are strongly driven by urine deposition by grazing ruminants. There is robust concern about applying nitrification inhibitor to mitigate nitrogen losses in global grasslands. However, the effect of dicyandiamide (DCD) on N2O emission rates and its driven factors remain unclear due to spatial heterogeneity. In the present study, we synthesized 133 group data from 69 published articles. It was indicated that effect size was -0.784±0.048 (P<0.0001) indicating a reduction of 54.34% in N2O emission rates. There was significant difference on effect size between different dose of nitrogen fertilization. Moderate dosage of DCD application was the best mitigation effect of 56.09%, which was significantly higher than light dosage of DCD application. Mixed effect model results revealed that precipitation, bulk density and air temperature could explain 16.93%, 12.31% and 3.02% variations in effect size. In addition, DCD application was an effective strategy to mitigate N2O emission rates in global grazed grasslands. [ABSTRACT FROM AUTHOR]

Surface drip fertigation has demonstrated promising results regarding the mitigation of nitrous oxide (N2O) emissions. The use of subsurface irrigation may offer the possibility of reducing these emissions further due to the modification of the soil moisture profile and N allocation, both of which affect the biochemical processes leading to N2O fluxes. However, the mitigation potential of subsurface irrigation combined with different mineral nitrogen (N) fertilizers (ammonium or nitrate-based, use of nitrification inhibitors) still needs to be evaluated. To respond to this need, a 2-year field experiment was set up in central Spain to test two different drip-fertigation systems (surface and subsurface at 30 cm depth) and four N fertilization treatments (control, calcium nitrate, and ammonium sulfate with or without the nitrification inhibitor 3,4-dimethylpyrazole phosphate, DMPP) in an irrigated maize (Zea mays L.) crop. Nitrous oxide emissions, mineral N concentrations (ammonium, NH4+, and nitrate, NO3−), and abundance of key N genes involved in nitrification and denitrification processes were measured in two soil layers (0–20 and 20–40 cm). Regardless of the irrigation system, ammonium sulfate gave the highest cumulative N2O losses in both campaigns, while calcium nitrate and the use of DMPP were the most effective strategies to abate N2O fluxes in the first and second years, respectively. Differences between irrigation systems were not statistically significant for cumulative N2O emissions, despite the clear effect on topsoil mineral N (higher NH4+ and NO3− concentrations in surface and subsurface drip, respectively). Nitrous oxide emissions were positively correlated with soil NH4+ concentrations. Gene abundances were not a trustworthy predictor of N2O losses in the 1st year, although a clear inhibitory effect of fertilization on microbial communities (i.e., ammonia oxidizers, nitrite reducers, and N2O reducers) was observed during this campaign. During the second year, nitrifying and denitrifying genes were affected by irrigation (with higher abundances in the 20–40 cm layer in subsurface than in surface drip) and by the addition of DMPP (which had a detrimental effect on gene abundances in both irrigation systems that disappeared after the fertigation period). In conclusion, the use of DMPP or calcium nitrate instead of ammonium sulfate may enhance the chances for an additional mitigation in both surface and subsurface irrigation systems. [ABSTRACT FROM AUTHOR]

Small rhizosphere exudates as chemical signals provide a green strategy to reduce nitrogen emissions and promote low-carbon agriculture. Specific biological nitrification inhibitors (BNIs) and biological denitrification inhibitors (BDIs) could retard nitrification and denitrification, thus reducing N 2 O emissions from terrestrial ecosystems. Enhanced nitrogen removal rates and lower N 2 O emissions are achieved by biological denitrification promoters (BDPs), such as root-derived fatty acid amides and sterols, and microbe-derived N -acyl-homoserine lactones (AHLs) in aquatic environments. Cultivating BNI/BDI/BDP-enhanced plant varieties, intercropping and rotation with BNI/BDI plants, developing green nitrogen fertilizers, and designing water purification bioagents based on small rhizosphere exudates are promising application measures for supporting green low-carbon agriculture. Low-carbon approaches to agriculture constitute a pivotal measure to address the challenge of global climate change. In agroecosystems, rhizosphere exudates are significantly involved in regulating the nitrogen (N) cycle and facilitating belowground chemical communication between plants and soil microbes to reduce direct and indirect emissions of greenhouse gases (GHGs) and control N runoff from cultivated sites into natural water bodies. Here, we discuss specific rhizosphere exudates from plants and microorganisms and the mechanisms by which they reduce N loss and subsequent N pollution in terrestrial and aquatic environments, including biological nitrification inhibitors (BNIs), biological denitrification inhibitors (BDIs), and biological denitrification promoters (BDPs). We also highlight promising application scenarios and challenges in relation to rhizosphere exudates in terrestrial and aquatic environments. [ABSTRACT FROM AUTHOR]

Copyright of Xinjiang Agricultural Sciences is the property of Xinjiang Agricultural Sciences Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Granular urea fertilizer applied at planting is prone to nitrogen (N) losses in certain environments. Enhanced efficiency fertilizers (EEFs) are developed to mitigate losses and optimize plant uptake. To determine the benefits of EEFs in grain yield and quality enhancement in Canada Western Red Spring (CWRS) wheat, an experiment was conducted from 2019 to 2022 at eight sites in Alberta and Saskatchewan, Canada. The effects of five N sources [urea; urea + urease inhibitor, N-(n-butyl)thiophosphoric triamide (NBPT); urea + nitrification inhibitor, nitrapyrin; urea + dual-inhibitor, NBPT + dicyandiamide; and polymer-coated urea, ESN® (Environmentally Smart Nitrogen®)] and four N rates (60, 120, 180, and 240 kg N ha−1) on CWRS wheat production were examined. Results indicated that N source affected grain yield in Dark Brown Chernozem soils but not in Black Chernozem or Dark Grey Luvisol soils. In Dark Brown Chernozem soils, a dual inhibitor increased grain yield by 3.1% and 3.9% relative to urea and polymer-coated urea, respectively, while all other EEFs attained similar results. The use of a dual inhibitor EEF led to greater net returns compared to urea and polymer-coated urea in the Dark Brown Chernozem soils. Grain protein concentration increased linearly with increasing N rate from 60 to 240 kg N ha−1. Generally, a rate of 120 kg N ha−1 was optimal for CWRS wheat grown in Canadian prairie conditions when coupled with EEFs, particularly a dual inhibitor, and grain yield and protein were often responsive. [ABSTRACT FROM AUTHOR]

Nitrogen (N) fertilizer management continues to be challenging due to potential nitrogen losses under variable weather conditions. This study aimed to evaluate the performance of nitrification inhibitors, nitrogen sources, and herbicides on in‐season nitrogen availability and agronomic indicators. A 2 site‐year field experiment was conducted in silty‐clay loam soil in the maize (Zea mays L.) phase of a maize–soybean rotation in Central Nebraska. The study included two herbicide treatments (Acuron and Resicore) and four nitrogen treatments: (1) anhydrous ammonia with a nitrification inhibitor, (2) anhydrous ammonia without a nitrification inhibitor, (3) urea with a nitrification inhibitor, and (4) urea without a nitrification inhibitor. Nitrogen sources had a more significant effect on NH4+‐N retention (300%–340% higher in anhydrous ammonia vs. urea) than nitrification inhibitors (14%–50% higher with inhibitor vs. without inhibitor) and herbicides. Similarly, nitrogen sources significantly affected NO3−‐N formation (58%–64% lower in anhydrous ammonia vs. urea) compared with nitrification inhibitors (7%–27% lower with inhibitor vs. without inhibitor) and herbicides. Nitrification inhibitors did not affect agronomic indicators. However, anhydrous ammonia increased grain yield by 1.1 Mg ha−1, partial factor productivity by 6 kg grain kg−1 N, agronomic efficiency by 5.5 kg grain kg−1 N, aboveground biomass N‐uptake by 34 kg N ha−1, grain N‐uptake by 15 kg N ha−1, nitrogen recovery efficiency by 33%, and residual total inorganic N by 6–40 kg N ha−1 compared to urea. These findings suggest that using the right fertilizer source, followed by nitrification inhibitor and herbicide, can be an effective strategy for conserving nitrogen and improving nitrogen use efficiency in maize. Core Ideas: Nitrogen source conserved nitrogen more than nitrification inhibitors and herbicides.Anhydrous ammonia retained four times higher soil NH4+‐N than urea.Nitrification inhibitors did not affect agronomic indicators and maize grain yield.Anhydrous ammonia improved agronomic indicators and maize grain yield more than urea.Right nitrogen source can improve NUE, followed by nitrification inhibitors and herbicides. [ABSTRACT FROM AUTHOR]

Producers in New Zealand's pasture-based, seasonal dairy sector are striving to reduce nitrogen (N) losses to the environment whilst maintaining or increasing farm profitability. This study examined the cost-effectiveness of stacking different combinations of five N leaching mitigation strategies within the whole farm system; 1) reduced N fertilizer input, 2) off-paddock infrastructure, 3) recycling N by growing maize silage on a dedicated area on the farm using effluent as a fertilizer source followed by a catch-crop, 4) dietary salt supplementation to dilute urinary N, and 5) applying a nitrification inhibitor (NI) to slow the release of nitrate in the soil. The reference point (baseline) was a typical current dairy farm (CF) system in the Waikato region of New Zealand. We modelled four Future Farm scenarios by stacking mitigation strategies as follows: baseline plus reduced N fertilizer input, reduced stocking rate, and off-paddock infrastructure (FF); FF plus a dedicated maize block (FFP); FFP plus dietary salt (FFPS); and FFPS plus NI (FFPSNI). These systems were modelled using the Whole Farm Model coupled with the Urine Patch Framework, and APSIM models, using observed climate and economic input data over five consecutive years from 2013-2018. Relative to CF, the FF system achieved a N leaching reduction of 31% with a reduction in profit of 16%. The FFP system had a smaller N leaching reduction (22%), but the reduction in profit was smaller (11%). The fully stacked system (FFPSNI) demonstrated the largest leaching reduction of 33%, but also the largest profit reduction of 27%, compared with the CF. Stacking these five N mitigation strategies can achieve substantial N leaching reductions at the farm-scale. Including a dedicated, effluent-fertilized maize block followed by a catch-crop as part of the stack can reduce the negative impact on profitability but has a trade-off in N leaching. Farmers will have to weigh up these compromises between profit and leaching, considering risk factors not modelled here. [ABSTRACT FROM AUTHOR]

Carbon and nitrogen compounds in agroecosystems have attracted much attention in recent years due to their key roles in crop production and their impacts on environment quality and/or climate change. Since fertilization profoundly disrupted the C and N cycles, several mitigation and/or adaptation strategies, including the application of farmyard manure (FYM) and/or urease and nitrification inhibitors (UI and NI), have been developed. The aim of this study was to evaluate the contents of soil organic carbon and its fractions, the total and mineral forms of nitrogen, as well as CO2 and N2O emissions under mineral and organic fertilization with and without urease and nitrification inhibitors in a maize agroecosystem. A two-year field study was carried out on Cambisols (silt) in Poland. The experiment scheme included nine treatments: C (the control without fertilization), UAN (Urea Ammonium Nitrate), UAN+UI, UAN+NI, UAN+UI+NI, FYM with N mineral fertilizer base, FYM with N mineral fertilizer base+UI, FYM with N mineral fertilizer base+NI, and FYM with N mineral fertilizer base+UI+NI. It was found that treatments fertilized with cattle FYM were higher sinks and sources of C and N compounds in comparison to the UAN plots. The organic carbon, humic and humin acid, and total nitrogen concentrations, in contrast to ammonium and nitrate nitrogen, were not affected by the inhibitors added. Nitrification and urease inhibitors were effective in decreasing N2O emissions only in treatments that were exclusively applied with UAN and had no significant influence on CO2 emissions. [ABSTRACT FROM AUTHOR]

Nitrification is a microbial process that converts ammonia (NH3) to nitrite (NO2-) and then to nitrate (NO3-). The first and rate-limiting step in nitrification is ammonia oxidation, which is conducted by both bacteria and archaea. In agriculture, it is important to control this process as high nitrification rates result in NO3- leaching, reduced nitrogen (N) availability for the plants and environmental problems such as eutrophication and greenhouse gas emissions. Nitrification inhibitors can be used to block nitrification, and as such reduce N pollution and improve fertilizer use efficiency (FUE) in agriculture. Currently applied inhibitors target the bacteria, and do not block nitrification by ammonia-oxidizing archaea (AOA). While it was long believed that nitrification in agroecosystems was primarily driven by bacteria, recent research has unveiled potential significant contributions from ammonia-oxidizing archaea (AOA), especially when bacterial activity is inhibited. Hence, there is also a need for AOA-targeting nitrification inhibitors. However, to date, almost no AOA-targeting inhibitors are described. Furthermore, AOA are difficult to handle, hindering their use to test or identify possible AOA-targeting nitrification inhibitors. To address the need for AOA-targeting nitrification inhibitors, we developed two miniaturized nitrification inhibition assays using an AOA-enriched nitrifying community or the AOA Nitrosospaera viennensis. These assays enable high-throughput testing of candidate AOA inhibitors. We here present detailed guidelines on the protocols and illustrate their use with some examples. We believe that these assays can contribute to the discovery of future AOA-targeting nitrification inhibitors, which could complement the currently applied inhibitors to increase nitrification inhibition efficiency in the field and as such contribute to a more sustainable agriculture. [ABSTRACT FROM AUTHOR]

Introduction: Ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) have been proven to be key microorganisms driving the ammonia oxidation process. However, under different fertilization practices, there is a lack of research on the impact of interaction between predators and AOA or AOB on nitrogen cycling at the multi-trophic level. Methods: In this study, a network-oriented microscopic culture experiment was established based on four different long-term fertilization practices soils. We used the nitrification inhibitors 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxide-3-oxyl (PTIO) and 3, 4-Dimethylpyrazole phosphate (DMPP) inhibited AOA and AOB, respectively, to explore the impact of interaction between protists and AOA or AOB on nitrogen transformation. Results: The results showed that long-term nitrogen application promoted the potential nitrification rate (PNR) and nitrous oxide (N2O) emission, and significantly increased the gene abundance of AOB, but had no obvious effect on AOA gene abundance. DMPP significantly reduced N2O emission and PNR, while PTIO had no obvious effect on them. Accordingly, in the multi-trophic microbial network, Cercozoa and Proteobacteria were identified as keystone taxa of protists and AOB, respectively, and were significantly positively correlated with N2O, PNR and nitrate nitrogen. However, Nitrososphaerota archaeon as the keystone species of AOA, had an obvious negative linkage to these indicators. The structural equation model (SEM) showed that AOA and AOB may be competitors to each other. Protists may promote AOB diversity through direct trophic interaction with AOA. Conclusion: The interaction pattern between protists and ammonia-oxidizing microorganisms significantly affects potential nitrification rate and N2O emission, which has important implications for soil nitrogen cycle. [ABSTRACT FROM AUTHOR]

A better understanding of the factors that reduce bundle-sheath cell leakage to CO2 (Փ), enhance 13C carbon isotope discrimination, and enhance the photosynthetic capacity of barley leaves will be useful to develop a nutrient- and water-saving strategy for dry-land farming systems. Therefore, barley plants were exposed to a novel nitrification inhibitor (NI) (3,4-dimethyl-1H-pyrazol-1-yl succinic acid) (DMPSA) and a urease inhibitor (UI) (N-butyl thiophosphorictriamide (NBPT)) with mulched drip fertigation treatments, which included HF (high-drip fertigation (370 mm) under a ridge furrow system), MF (75% of HF, moderate-drip fertigation under a ridge furrow system), LF (50% of HF, low-drip fertigation under a ridge furrow system), and TP (traditional planting with no inhibitors or drip fertigation strategies). The results indicated that the nitrification inhibitor combined with mulched drip fertigation significantly reduced bundle-sheath cell leakage to CO2 (Փ) as a result of increased soil water content; this was demonstrated by the light and CO2 response curves of the photosynthesis capacity (An), the apparent quantum efficiency (α), and the 13C-photosynthate distribution. In the inhibitor-based strategy, the use of the urease and nitrification inhibitors reduced Փ by 35% and 39% compared with TP. In the NI-HF strategy, it was found that barley could retain the maximum photosynthesis capacity by increasing the leaf area index (LAI), An, rubisco content, soluble protein, dry matter per plant, and productivity. The CO2 and light response curves were considerably improved in the NI-HF and NI-MF treatments due to a higher 13C carbon isotope (Δ‰), respiration rate (Rd), and Ci/Ca, therefore obtaining the minimum Փ value. With both inhibitors, there was a significant difference between HF and LF drip fertigation. The NI-MF treatment significantly increased the grain yield, total chlorophyll content, WUE, and NUE by 52%, 47%, 57%, and 45%, respectively. Collectively, the results suggest that the new nitrification inhibitor (DMPSA) with HF or MF mulched drip fertigation could be promoted in semi-arid regions in order to mitigate bundle-sheath cell leakage to CO2 (Փ), without negatively affecting barley production and leading to the nutrient and water use efficiency of barley. [ABSTRACT FROM AUTHOR]

One-time fertilization with controlled-release urea (CRU) is a research hotspot for its lower labor cost and stability of nitrogen (N) supply for rice growth. Yet the fertilizer formulation needs to be further improved to better adjust the N supplement to meet the demand of rice plants and obtain a higher grain yield. Therefore, the effects of novel fertilizer formulations composed of CRU, urease inhibitor (UI) and nitrification inhibitor (NI) on the rice growth and photosynthetic characteristics as well as high-yield formation were tested through a two-year field experiment. The result indicated that the combined use of CRU and UI treatment can achieve higher yields than with CRU at the same N application level. Meanwhile, with a 20% reduction of N use, one-time application of CRU + UI can obtain the same high yield as the conventional split application of urea. Compared with conventional fertilization and CRU treatment, the CRU + UI treatment had suitable leaf area and biomass accumulation at the vegetative growth stage and high effective stem tiller rate. More post-anthesis dry matter accumulation, higher net photosynthesis rate and low senescence rate were guaranteed for its high yield and nitrogen agronomic efficiency. [ABSTRACT FROM AUTHOR]

Nitrification inhibitor is essential for increasing the nitrogen utilization efficiency of agricultural plants, thus reducing environmental pollution and increasing crop yield. However, the easy volatilization and limited functional property is still the bottleneck of nitrification inhibitors. Herein, a novel water-soluble polymeric nitrification inhibitor was synthesized through the copolymerization of acrylamide and bio-based acrylic acid, which was synthesized from biomass-derived furfural, and the complexation of carboxyl groups and 3,4-dimethylpyrazole. The results showed that the nitrification inhibitor was an amorphous polymer product with a glass transition temperature of 146 °C and a thermal decomposition temperature of 176 °C, and the content of 3,4-dimethylpyrazole reached 2.81 wt%, which was 115% higher than our earlier product (1.31 wt%). The polymeric nitrification inhibitor can inhibit the activity of ammonia-oxidizing bacteria effectively, thus inhibiting the conversion of ammonium nitrogen to nitrate nitrogen and converting the insoluble phosphate into soluble and absorbable phosphate. By introducing a copolymer structure with a strong flocculation capacity, the polymeric nitrification inhibitor is further endowed with a soil-loosening function, which can increase the porosity of soil to improve the soil environment. Therefore, the nitrification inhibitor can be used in water-soluble and liquid fertilizers, as well as in high tower melting granulated compound fertilizers. [ABSTRACT FROM AUTHOR]

Biological nitrification inhibitors (BNIs) are released from plant roots and inhibit the nitrification activity of microorganisms in soils, reducing NO 3 ‒ leaching and N 2 O emissions, and increasing nitrogen- use efficiency (NUE). Several recent studies have focused on the identification of new BNIs, yet little is known about the genetic loci that govern their biosynthesis and secretion. We applied a combined transcriptomic and metabolomic analysis to investigate possible biosynthetic pathways and transporters involved in the biosynthesis and release of BNI 1,9-decanediol (1,9-D), which was previously identified in rice root exudates. Our results linked four fatty acids, icosapentaenoic acid, linoleate, norlinolenic acid, and polyhydroxy-α,ω-divarboxylic acid, with 1,9-D biosynthesis and three transporter families, namely the ATP-binding cassette protein family, the multidrug and toxic compound extrusion family, and the major facilitator superfamily, with 1,9-D release from roots into the soil medium. Our finding provided candidates for further work on the genes implicated in the biosynthesis and secretion of 1,9-D and pinpoint genetic loci for crop breeding to improve NUE by enhancing 1,9-D secretion, with the potential to reduce NO 3 ‒ leaching and N 2 O emissions from agricultural soils. [ABSTRACT FROM AUTHOR]

Environmental context: Ammonia emissions from inorganic nitrogen fertilisers used in agriculture can impact air quality, human health and ecology. This study quantifies such emissions and their controlling factors from UK and Ireland agricultural soils. Emissions are variable and, from non-urea fertilisers, substantially exceed maximum emission factors used by the UK Department for Environment, Food and Rural Affairs. This suggests that UK emission factors need to be refined further, with consideration of inter alia land-use, fertiliser type, soil pH and chemical inhibitors. Rationale: Ammonia (NH3) emissions from inorganic nitrogen (N) fertilisers applied to agricultural soils have negative implications for environmental quality and human health. Despite this, efforts to reduce NH3 emissions in the UK have achieved limited success. This study aims to provide an overview of NH3 emissions from UK and Ireland agricultural soils receiving N fertilisers, their regulating factors and the potential role of inhibitors in reducing current NH3 losses. Methodology: A systematic literature search was performed to identify relevant experimental data and studies, and the extracted data (total of 298 field fertilisation events) were categorised and analysed systematically. Results: NH3 emissions ranged from −4.00 to 77.00% of applied fertiliser-N lost as NH3. In addition to fertiliser type, NH3 losses were also significantly affected by land-use type and soil pH. Urease and combined urease and nitrification inhibitors significantly reduced emissions by 74.50 and 70.00% compared to uninhibited-urea respectively. Discussion: In addition to fertiliser types, land-use and soil pH were found as factors for consideration as modifiers to the maximum NH3 emission factor (EFmax) values currently used in the UK, in order to improve estimations of NH3 emissions, particularly from non-urea fertilisers. This is imperative as NH3 losses exceeded current EFmax limits, particularly in the case of non-urea fertilisers, by ~34%, implying that NH3 emissions estimated from UK synthetic fertiliser require further refinements. NH3 losses are not completely inhibited, inhibitors cannot be solely relied upon for tackling NH3 emissions from UK and Ireland fertiliser usage and further research is needed into alternative mitigation methods to further reduce NH3 losses. Environmental context. Ammonia emissions from inorganic nitrogen fertilisers used in agriculture can impact air quality, human health and ecology. This study quantifies such emissions and their controlling factors from UK and Ireland agricultural soils. Emissions are variable and, from non-urea fertilisers, substantially exceed maximum emission factors used by the UK Department for Environment, Food and Rural Affairs. This suggests that UK emission factors need to be refined further, with consideration of inter alia land-use, fertiliser type, soil pH and chemical inhibitors. This article belongs to the collection Dedication to Prof. Edward Tipping. [ABSTRACT FROM AUTHOR]

Soil protease plays a fundamental role in soil nitrogen (N) transformations. Soil N and phosphorus (P) management significantly influence soil protease activity. However, the impacts of N and P combined modification on soil protease remain unclear. A better understanding of the activity and dynamic of soil protease could provide new insights into soil N cycling and available N supply. This study aimed to quantify the influences of combined effects of N and P managements on soil protease activities and decipher the potential mechanism from the perspectives of soil chemical properties, functional microbes, and functional genes. The nitrification inhibitor 3, 4‐dimethylpyrazole phosphate (DMPP) application or phosphate‐solubilizing bacteria (PSB) Klebsiella inoculation significantly increased soil protease activity (23.39% and 70.99%, respectively) and ammonium N (NH4+–N) contents, relative to the blank control. However, compared with the DMPP or PSB alone application, the combined applications of DMPP and PSB significantly decreased protease activity, implying that an antagonistic effect on soil protease activity was generated. The abundances of genus Klebsiella were stimulated by the DMPP or PSB but significantly inhibited by the combined additions of DMPP and PSB. The DMPP and PSB applications also significantly changed soil microbial communities and led to more complicated soil microbial co‐occurrence networks. Soil protease activity had a significantly positive correlation with the normalized abundances of tri and clpX genes. Our findings suggested that the combined additions of DMPP and PSB generated an antagonistic effect on soil protease activity and that the antagonistic effect was directly associated with soil NH4+–N and NO3−–N contents, P fractions, and functional gene abundances. [ABSTRACT FROM AUTHOR]

A two years field experiment was conducted at the Agronomy field unit, Zonal Agricultural Research Station, UAS-B, GKVK, Bengaluru during summer, 2022 and 2023 to assess the efficacy of urease and nitrification inhibitors on productivity and profitability of aerobic rice. The experiment was laid out in Randomized Complete Block Design with nine treatments (Urea, Urea + HQ @ 4000 mg kg-1 urea, Urea + HQ @ 8000 mg kg-1 urea, Urea + HQ @ 12000 mg kg-1 urea, Urea + DCD @ 4000 mg kg-1 urea, Urea + DCD @ 8000 mg kg-1 urea, Urea + DCD @ 12000 mg kg-1 urea, Neem coated urea and Absolute control), each replicated thrice. Significantly higher plant height (72.27 cm), number of tillers plant-1 (22.83), dry matter production (53.70 g plant-1), number of green leaves plant-1 (85.03) and leaf area (2108 cm² plant-1) at 90 DAS and panicle length (22.14 cm), grain weight (2.93 g), grain yield (4717 kg ha-1), straw yield (5796 kg ha-1) and gross returns (Rs.106845 ha-1) were recorded with application of Urea + HQ @ 12000 mg kg-1 urea compared to other treatments on pooled basis. However, application of neem coated urea found to be more economical with significantly higher net returns (Rs.55662 ha-1) and B:C (2.28) compared to other treatments. [ABSTRACT FROM AUTHOR]

Animal manures are valuable multi-nutrient fertilizers, but their short-term nitrogen (N) use efficiency (NUE) by plants is low, bearing the potential of harmful N losses to the environment, such as nitrate (NO-3) leaching. To develop strategies to increase the NUE of cattle slurry, a comprehensive understanding of slurry N dynamics in the soil-plant system is needed. In a 57-day microcosm experiment in the greenhouse, we assessed the effect of different slurry treatments on slurry N turnover in the soil and its uptake by ryegrass (Lolium multiflorum var. Westerwoldicum). Employing a two-factorial design, 15N cattle slurry (SLU), 15N anaerobically digested cattle slurry (SLA), and 15N anaerobically digested cattle slurry plus biochar (SLA+) were combined with and without the nitrification inhibitor 3,4-dimethyl-1H-pyrazole monophosphate (DMPP). As references, a mineral fertilizer (MIN) and an unfertilised treatment (N0) were included. The 15N recovery, hence NUE, in plant biomass was higher for SLA than for SLU, while recovery in soil at 55 days after set-up showed an opposite trend, with over 45% of N from SLU still being recovered in soil. DMPP and biochar only marginally affected NUE and fertilizer N recovery in soil. Although 15N recovery in soil was highest for SLU, residual N leaching from SLU was low (<1% of added N). We attribute this to the limited presence of slurry N in mineral forms at this point of time, with the majority being stored in the non-microbial organic soil N pool. Leaching of residual N from MIN was significantly higher for MIN than for SLU, while SLA and SLA+ ranged in between. Overall, anaerobic digestion appeared suitable for increasing NUE of cattle slurry, but further investigations under field conditions are necessary in order to assess its potential to reduce nitrate leaching in the long-term. [ABSTRACT FROM AUTHOR]

Urea splitting and the use of stabilized ureas in corn (Zea mays L.) crops are management strategies that increase urea efficiency and reduce nitrogen (N) losses by volatilization and leaching. This study aimed to evaluate the effects of urea stabilized with urease inhibitor (UI) and nitrification inhibitor (NI) compared to conventional urea applied at three different schedules, on corn grain yield and the dynamics of inorganic nitrogen on an Amazonian Cerrado soil, Brazil. Two experiments were carried out, one in 2019 and the other one in 2021, in a randomized block design with four replications. Treatments were arranged in a factorial scheme (3 × 3), with three types of urea (urea, U; UI; and NI) and three application schedules (100% at planting, 30% at planting and 70% as topdressing, and 30% at planting and two topdressings with 35% N). In 2019, compared to U and UI, NI increased corn yield when 100% of urea was applied at planting. Regardless of the splitting management, NI ensured the same yields. In 2021, urea splitting was required to improve corn yields, and UI promoted higher yield in all urea application schedule. In 2019 and 2021, both NI and UI, respectively, ensured higher inorganic N levels in the soil, especially after the first topdressing. These N contents are reflected in yield gains. Urea with nitrification or urease inhibitor may be a relevant option for managing nitrogen fertilization in corn crops in the Amazonian Cerrado. Core Ideas: Nitrification or urease inhibitors may be an option for managing nitrogen in corn crops in the Amazonian Cerrado.Edaphoclimatic conditions influence the stabilized ureas efficiency in corn cultivation in the Amazonian Cerrado.Urea with urease or nitrification inhibitor ensured higher level of available nitrogen in the soil for plants. [ABSTRACT FROM AUTHOR]

Opportunities exist to reduce nitrous oxide (N2O) emissions from nitrogen (N) fertilizers using enhanced efficiency fertilizers (EEFs) and managing application timing. This study examined (1) application timing (fall/spring) and (2) fertilizer N source on N2O emissions, yield, and N uptake of Canadian hard red spring wheat (Triticum aestivum L.) in Southern Manitoba. Fertilizer N sources included granular urea and four EEF products: (1) polymer‐coated urea (environmentally smart nitrogen [ESN]); (2) urea plus nitrification inhibitor (eNtrench); (3) urea plus urease inhibitor (Limus); and (4) urea plus nitrification and urease inhibitor (SuperU). Nitrification‐inhibited products most consistently reduced N2O emissions while maintaining productivity. Compared to urea alone, urea + eNtrench was most effective in reducing cumulative N2O emissions by 47%–64% at four of six site‐years. SuperU reduced N2O emissions by 37%–57% at three of six site‐years. ESN and urea + Limus did not affect emissions in most years. Wheat yield, protein, and N uptake were unaffected by N source in five of six site‐years. Compared to spring, fall application gave greater N2O emissions by 33%–67% at three of six site‐years due to spring‐thaw emissions. Fall was inferior to spring application in wetter site years with lower yield, protein, and N uptake. Overall, nitrification‐inhibited products—either alone or with a urease inhibitor—are a promising tool to reduce N2O emissions while maintaining wheat productivity in Manitoba. However, given that there were few consistent increases in yield or protein, the additional cost of the inhibitors will be a barrier to adoption. Core Ideas: EEF products with nitrification and nitrification/urease inhibitors consistently reduced N2O emissions.Controlled release urea and urease‐inhibited urea did not reduce N2O emissions.Fall application of urea increased N2O emissions in three site‐years compared to spring application.The nitrification inhibitors applied with urea in fall or spring were effective to reduce N2O emissions.Overall, fall application decreased yield, grain protein, and N uptake in relatively wet years. [ABSTRACT FROM AUTHOR]

The use of inhibitors retain nitrogen as ammonium in soil, giving plants ample time for its uptake. This can reduce nitrous oxide (N2O) emissions, but extended retention may increase ammonia (NH3) volatilization. This study assessed the efficacy of coated urea fertilizers in reducing greenhouse gas (GHG) emissions and NH3 volatilization in rice fields. A field experiment with Pusa 44 rice in the kharif seasons of 2019 and 2020 compared unfertilized control (No N), prilled urea (PU), nitrification inhibitors (NIs): neem oil-coated urea (NCU), karanj oil-coated urea, and dual inhibitor (DI: Limus + NCU). The coated urea fertilizers were analysed with scanning electron microscopy, fourier transform infrared spectrometry, and energy-dispersive spectroscopy. Compared to PU, DI reduced N2O emissions by 23.7%, methane by 11.9%, and NH3 by 29.8%. DI also reduced NH3 emissions by 36–39% compared to other NIs. Overall, DI can lower the global warming potential of rice cultivation in trans Indo-Gangetic plains region by 17.1% for both direct and indirect emissions, suggesting its significant potential to reduce India's contribution to total agricultural GHG emissions.

IntroductionThrough the combined use of two nitrification inhibitors, Dicyandiamide (DCD) and chlorate with nitrogen amendment, this study aimed to investigate the contribution of comammox Nitrospira clade B, ammonia oxidizing bacteria (AOB) and archaea (AOA) to nitrification in a high fertility grassland soil, in a 90-day incubation study.MethodsThe soil was treated with nitrogen (N) at three levels: 0 mg-N kg-1 soil, 50 mg-N kg-1 soil, and 700 mg-N kg-1 soil, with or without the two nitrification inhibitors. The abundance of comammox Nitrospira, AOA, AOB, and nitrite oxidising bacteria (NOB) was measured using qPCR. The comammox Nitrospira community structure was assessed using Illumina sequencing.Results and DiscussionThe results showed that the application of chlorate inhibited the oxidation of both NH4+ and NO2- in all three nitrogen treatments. The application of chlorate significantly reduced the abundance of comammox Nitrospira amoA and nxrB genes across the 90-day experimental period. Chlorate also had a significant effect on the beta diversity (Bray-Curtis dissimilarity) of the comammox Nitrospira clade B community. Whilst AOB grew in response to the N substrate additions and were inhibited by both inhibitors, AOA showed litle or no response to either the N substrate or inhibitor treatments. In contrast, comammox Nitrospira clade B were inhibited by the high ammonium concentrations released from the urine substrates. These results demonstrate the differential and niche responses of the three ammonia oxidising communities to N substrate additions and nitrification inhibitor treatments. Further research is needed to investigate the specificity of the two inhibitors on the different ammonia oxidising communities.

High-efficient regulation and management of nitrogen fertilizers based on their transformation characteristics in soil is one of the most important measures to enhance fertilizer utilization efficiency for less pollution. In this study, two incubation experiments (with soil moisture content at 60% of field water holding capacity and temperature at 25 °C) were conducted to explore the transformation of different nitrogen fertilizers in the calcareous-fluvo-aquic soil and the effects of ammonium thiosulfate (ATS) as a regulator on urea-N transformation. Four types of nitrogen fertilizers (namely urea, ammonium sulfate, ammonium chloride, and ammonium thiosulfate (ATS)) were used as nitrogen sources. Soil samples were collected at regular intervals to determine the contents of soil NH4 + -N, NO2 − -N and NO3 − -N. At the same time, five treatments were set to investigate the regulatory effect of ATS on urea-N transformation: 1) CK (no nitrogen fertilizer applied); 2) U (urea only); 3) U+ATS1 (ATS added at 30 mg/kg sulfur content): 4) U+ATS2 (ATS added at 60 mg/kg sulfur content); 5) U+ATS3 (ATS added at 90 mg/kg sulfur content). Finally, an analysis was performed on the dynamic changes of NH4 + -N, NO2 − -N and NO3 − - N. The results showed that there were significant differences in the transformation process among different types of nitrogen fertilizers in calcareous-fluvo-aquic soil . Among them, urea performed the highest hydrolysis rate and nitrification intensity, followed by ammonium sulfate. The soil treated with ammonium chloride shared a lower apparent nitrification rate than that of urea and ammonium sulfate ( P <0.05) from 7 to 21 days, due to the inhibitory effect of Clon soil nitrification. However, the ATS treatment showed the lowest NH4 + -N content within the first 7 days of incubation, which should be beneficial to reduce ammonia volatilization in the initial period of fertilizer application. While the opposite result was found after 7 days of incubation. Soil NH4 + -N content in the treatment with ATS was higher by 7.4 to 21.8 times than that of urea, 4.7 to 13.5 times than that of ammonium sulfate, and 0.9 to 10.9 times than that of ammonium chloride during 10 to 21 days, which was equivalent to CK value until to 24 days of incubation. The peak time of NO3 − -N content was delayed by 14, 10, and 7 days, compared with the urea, ammonium sulfate, and ammonium chloride, respectively. Soil NO3 − -N content and the apparent nitrification intensity were reduced by 21.5% to 47.7% and 7.5% to 36.0%, respectively, during the 24 days of incubation, compared with the urea. When ATS was used in combination with urea as a nitrogen regulator at a dosage above 60 mg/kg (calculated using sulfur content), there were inhibitory effects on urea hydrolysis and nitrification, which increased with the ATS amount increasing. There were positive implications to reduce the nitrogen loss for the high fertilizer utilization efficiency. However, nitrite accumulation occurred after all four nitrogen fertilizers were applied into soil. The ATS treatments demonstrated a significantly higher accumulation and longer duration than urea, ammonium sulfate, and ammonium chloride. Similar trends were observed when ATS was used as a nitrogen regulator. The increasing ATS dosages resulted in the longer nitrite retention time, higher content and peak values in soil, as well as the delayed peak occurrence. The field application effects of ATS and scientific application methods, as well as its environmental effects are need to further study. [ABSTRACT FROM AUTHOR]

Peanuts (Arachis hypogaea L.) is an important oil and nitrogen (N) fixing crop. Urease inhibitors (UIs) and nitrification inhibitors (Nis) can mitigate the release of N and reduce the harmful effects of excessive N concentrations. However, the effect of these inhibitors on the soil nutrient-microbial activity-plant growth system is unknown in peanut. The purpose of this study was to investigate the effects and mechanism of N-(n-butyl) thiophosphoric triamide (NBPT), 3,4-dimethylpyrazole phosphate (DMPP) and sulfur-coated urea (SCU) on peanut. The results showed that comparing with urea alone, adding NBPT + DMPP inhibited the urea hydrolysis better and decreased the concentration of NH4+-N + NO3−-N by 20.8% in soil. Therefore, it increased the net photosynthetic rate, promoted the development of roots even the absorption of N by peanut, with N use efficiency (NUE) up to 20.8%. The effect of NBPT + DMPP on microorganism was better than that of NBPT alone, which considerably impacted the structure and abundances of aonia oxidizing bacteria (AOB) but not ammonia-oxidizing archaea (AOA). Specifically, g_Nitrosospira and g_Nitrosomonas decreased by 46.9% and 2.2% respectively, and g(c) Betaproteobacteria increased. Furthermore, when combined with SCU on this basis, the overall effect was clearer. [ABSTRACT FROM AUTHOR]

This work was aimed at synthesizing a number of new complex compounds, nitrification inhibitors containing Zn2+, and determining their structure, composition and biological activity. Four substances with different ratios of ligands (4-amino-1,2,4- trazole (ATC)) and dicyandiamide (DCD)) were synthesized. Some physicochemical properties were determined, such as thermal behavior and solubility of complexes in pure KAS-28 (a saturated solution of urea and ammonium nitrate containing 28% nitrogen) and its 50 % solution. The content of Zn2+ in each substance was determined. The functional groups belonging to the ligands were established using IR spectroscopy. It was established that the attachment of ATC in solution takes place monodentately to one zinc atom through the N1 atom, and in crystals it occurs bidentately to two zinc atoms through the N1 and N2 atoms (1, 2-coordination). The attachment of DCD, most likely, proceeds through the C=NH group. The level of biological activity of complex compounds was determined by the potentiometric method. A direct measurement of the concentration of NH4+ and NO3- ions was carried out. The greatest influence on the nitrification process was found in the complex with the following probable empirical formula [Zn(ATC)2(DCD)1(H2O)1]SO4. When using it, the smallest loss of ammonium and the smallest formation of nitrates in the soil were observed. This indicates the influence on both stages of nitrification. [ABSTRACT FROM AUTHOR]

Nitrification inhibitors (NIs) are considered as an effective strategy for reducing nitrification rate and related environmental nitrogen (N) loss. However, whether plant-derived biological NIs had an advantage over chemical NIs in simultaneously inhibiting nitrification rate and N2O production remains unclear. Here, we conducted an aerobic 15N microcosmic incubation experiment to compare the effects of a biological NI (methyl 3-(4-hydroxyphenyl) propionate, MHPP) with three chemical NIs, 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin), dicyandiamide (DCD), and 3,4-dimethylpyrazole phosphate (DMPP) on (i) gross N mineralization and nitrification rate and (ii) the relative importance of nitrification and denitrification in N2O emission in a calcareous soil. The results showed that DMPP significantly inhibited m_gross rate (P < 0.05), whereas DCD, nitrapyrin, and MHPP only numerically inhibited it. Gross N nitrification (n_gross) rates were inhibited by 9.48% in the DCD treatment to 51.5% in the nitrapyrin treatment. Chemical NIs primarily affected the amoA gene abundance of ammonia-oxidizing bacteria (AOB), whereas biological NIs affected the amoA gene abundance of ammonia-oxidizing archaea (AOA) and AOB. AOB's community composition was more susceptible to NIs than AOA, and NIs mainly targeted Nitrosospira clusters of AOB. Chemical NIs of DCD, DMPP, and nitrapyrin proportionally reduced N2O production from nitrification and denitrification. However, the biological NI MHPP stimulated short-term N2O emission and increased the proportion of N2O from denitrification. Our findings showed that the influence of NIs on gross N mineralization rate (m_gross) was dependent on the NI type. MHPP exhibited a moderate n_gross inhibitory capacity compared with the three chemical NIs. The mechanisms of chemical and biological NIs inhibiting n_gross can be partly attributed to changes in the abundance and community of ammonia oxidizers. A more comprehensive evaluation is needed to determine whether biological NIs have advantages over chemical NIs in inhibiting greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

The use of biological nitrification inhibitors (BNIs) holds a great potential to effectively reduce nitrogen losses from agroecosystems and conforms with the current move toward ecological-intensified agriculture. Knowledge of the activity of BNIs to soil nitrifiers is limited and is generally based on a single Nitrosomonas europaea bioassay. We determined the in vitro activity of multiple plant-derived compounds as BNIs such as (i) root-derived compounds [sakuranetin, methyl 3-(4-hydroxyphenyl)-propionate (MHPP), and zeanone]; (ii) other phytochemicals (caffeic, quinic, chlorogenic, and shikimic acids); and (iii) analogs of statins (simvastatin), triazoles (1-butyl-4-propyltriazole, 1,4-dibutyltriazole), and zeanone (2-methoxy-1,4-naphthoquinone) on distinct soil-derived ammonia-oxidizing bacteria (AOB) (Nitrosospira multiformis and Nitrosomonas europaea), ammonia-oxidizing archaea (AOA) (Candidatus Nitrosotalea sinensis and Candidatus Nitrosocosmicus franklandianus), and a nitrite-oxidizing bacterium (NOB) (Nitrobacter sp.). Our results indicate that AOA were more sensitive than AOB to BNIs. Sensitivity within the AOA group was BNI dependent, unlike AOB, for which N. multiformis was consistently more sensitive than N. europaea. Several compounds were inhibitory to Nitrobacter sp. with MHPP and caffeic acid being more potent against NOB compared to the ammonia-oxidizing strains, an observation with potential implications for soil quality and productivity. Overall, zeanone was the most potent NI against ammonia oxidizers, while caffeic acid was the most potent BNI against Nitrobacter sp. We provide pioneering evidence for the activity range of multiple BNIs on soil nitrifiers, stress the need for revisiting the biological screening systems currently used for BNI determination, and advocate for a more thorough monitoring of the impact of BNI candidates on a range of target and non-target microorganisms. IMPORTANCE Synthetic nitrification inhibitors are routinely used with nitrogen fertilizers to reduce nitrogen losses from agroecosystems, despite having drawbacks like poor efficiency, cost, and entry into the food chain. Plant-derived BNIs constitute a more environmentally conducive alternative. Knowledge on the activity of BNIs to soil nitri fiers is largely based on bioassays with a single Nitrosomonas europaea strain which does not constitute a dominant member of the community of ammonia-oxidizing microorganisms (AOM) in soil. We determined the activity of several plant-derived molecules reported as having activity, including the recently discovered maize-isolated BNI, zeanone, and its natural analog, 2-methoxy-1,4-naphthoquinone, on a range of ecologically relevant AOM and one nitrite-oxidizing bacterial culture, expanding our knowledge on the intrinsic inhibition potential of BNIs toward AOM and highlighting the necessity for a deeper understanding of the effect of BNIs on the overall soil microbiome integrity before their further use in agricultural settings. [ABSTRACT FROM AUTHOR]

Urease inhibitors (UIs) and nitrification inhibitors (NIs) can greatly reduce nitrogen loss in agriculture soil. However, design and synthesis of an efficient and environmentally friendly dual-functional inhibitor is still a great challenge. Herein, four metal–organic salts (MOSs) based on heterogeneous conformations of the ligand N1,N1,N2,N2-tetrakis(2-fluorobenzyl)ethane-1,2-diamine (L), namely, [2HL]2+·[MCl4]2− (M = Cu, Zn, Cd, and Co), have been synthesized by the "second sphere" coordination method and structurally characterized in detail. Single crystal X-ray diffraction (SCXRD) analyses reveal that the four MOSs are 0D supramolecular structures containing [2HL]2+ and [MCl4]2−, which are connected through non-covalent bonds. Furthermore, the urease and nitrification inhibitory activities of MOSs are evaluated, showing excellent nitrification inhibitory activity with the nitrification inhibitory rate as high as 70.57% on the 28th day in soil cultivation experiment. In particular, MOS 1 shows significant urease inhibitory activity with half maximal inhibitory concentration (IC50) values of 0.89 ± 0.01 μM (0.5 h) and 1.87 ± 0.01 μM (3 h), which can serve as a dual-functional inhibitor. [ABSTRACT FROM AUTHOR]

The nitrogen removal performance and mechanisms of Bacillus subtilis H1 isolated from a mariculture environment were investigated. Strain H1 efficiently removed NH4+-N, NO2−-N, and NO3−-N in simulated wastewater with removal efficiencies of 85.61%, 90.58%, and 57.82%, respectively. Strain H1 also efficiently degraded mixed nitrogen (NH4+-N mixed with NO2−-N and/or NO3−-N) and had removal efficiencies ranging from 82.39 to 89.54%. Nitrogen balance analysis revealed that inorganic nitrogen was degraded by heterotrophic nitrification–aerobic denitrification (HN-AD) and assimilation. 15N isotope tracing indicated that N2O was the product of the HN-AD process, while N2 as the final product was only detected during the reduction of 15NO2−-N. The nitrogen assimilation and dissimilation pathways by strain H1 were further clarified using complete genome sequencing, nitrification inhibitor addition, and enzymatic activity measurement, and the ammonium oxidation process was speculated as NH4+ → NH2OH → NO → N2O. These results showed the application prospect of B. subtilis H1 in treating mariculture wastewater. [ABSTRACT FROM AUTHOR]

The study was focused on identification of potentially effective and environmentally feasible nitrification inhibitors for cauliflower in order to minimize the losses of applied N fertilizers under mid hill conditions. Field experiment was conducted for two consecutive years (2018–19 & 2019–20) on late sown cauliflower cv. Pusa Snowball K1 with eight different doses of inhibitors supplemented with NPK fertilizers and farmyard manure (FYM) in Randomized Block Design (RBD) replicated thrice. Results showed that recommended dose of fertilizer [N, P & K (125:76:72 kg/ha)] with neem cake (20 g/kg soil) + FYM (250 q/ha) registered maximum pooled NPK concentration in curd (3.40, 0.69 & 1.93%), leaf (2.85, 0.49 & 1.86%) and root (1.34, 0.35 & 1.24%). Maximum plant NPK uptake (95.4, 29.4 & 61.4 kg/ha) and curd yield (283.97 q/ha) on pooled basis was recorded under the similar treatment, the results were comparable to CaC2 treatment with NPK uptake of 92, 28 & 58 kg/ha, respectively and curd yield of 278.90 q/ha. Application of neem cake resulted in highest soil NH4+-N accumulation (137.71 kg/ha) with comparatively lower NO3--N retention (46.18 kg/ha). Regarding economics, maximum net returns (Rs/ha 4,36,662) with a highest benefit: cost ratio of 3.89 was registered under melia application@ 20 g/kg soil. Besides neem cake, melia provided better results on crop growth over pomegranate application. Therefore, two years of field study identified neem cake and melia as prominent and cost effective nitrification inhibitor module for cauliflower under mid hilly conditions. [ABSTRACT FROM AUTHOR]

3,4-Dimethylpyrazole phosphate (DMPP) is acknowledged as one of the most efficient nitrification inhibitors (NIs); however, researchers have suggested that its effectiveness needs to be further improved. The authors combined the biostimulant seaweed extract (SE) with DMPP and conducted an indoor incubation experiment to initially investigate the impact of the influence of SE on the degradation and effectiveness of DMPP. Meanwhile, a method for the extraction and determination of DMPP was developed. DMPP performed better, with a longer effective time in loess than black soil, and SE showed a delayed effect on DMPP degradation of DMPP at the beginning of the incubation and then accelerated the degradation process. This was attributed to the adsorption effect of SE on DMPP, consequently reducing its effectiveness. The SE delayed the hydrolysis of urea in various soils; however, no significant impact on urease activity was observed (P < 0.05) (P < 0.05). Furthermore, it also increased potential nitrification rate (PNR) from 10 to 21 days and promoting the rapid transformation of NH4 +-N in black soil. The SE reduced PNR within 21 days and inhibited nitrification in loess. In addition, the SE appeared to mitigate the adverse effects of excessive nitrogen on microorganisms The combination of DMPP and SE was not conducive to the inhibition of soil nitrification, and this formulation in field applications requires further investigation. [ABSTRACT FROM AUTHOR]

Aims: Arbuscular mycorrhizal (AM) fungi establish root symbioses that can improve acquisition of nutrients such as nitrogen (N) from soils, leading to improvements in host plant growth. Previously, we showed that applying AM fungal necromass to the rhizosphere could stimulate plant growth. Here we investigated the interactions between AM fungi (living or dead) and ammonia oxidizers (AO), a key group of soil prokaryotes involved in soil N cycling, to understand the effects of these interactions on plant N levels. We were interested in whether the necromass contained any significant biological nitrification inhibitory (BNI) activity that could account for the previously suggested antagonism between AM fungi and AO. Methods: We set up a compartmented pot experiment with Andropogon gerardii as a host plant, which included rhizosphere (amended with living and/or dead AM fungal biomass) and a root-free zone. The latter contained a mesh bag with 15N-labelled plant litter. Results: Inoculation with living AM fungus enhanced plant biomass and nutrient acquisition, including increased transfer of 15N from the mesh bags to the plants. Additionally, AO bacteria but not archaea were significantly suppressed in the mesh bags. In contrast, AM fungal necromass had minimal effect on plant biomass and nutrient acquisition. Surprisingly, it stimulated the growth of both AO bacteria and archaea in the rhizosphere of non-mycorrhizal plants. Conclusions: Based on the above, we found no support for AM fungi suppressing the AO through an elusive BNI production. Rather, it seems that the main mechanism of AM fungal-AO interaction is substrate competition. [ABSTRACT FROM AUTHOR]