Biochar application increases sorption of nitrification inhibitor 3,4-dimethylpyrazole phosphate in soil

Fabrication of metal-organic salts with heterogeneous conformations of a ligand as dual-functional urease and nitrification inhibitors

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.

The fate of nitrification and urease inhibitors in simulated bank filtration

The application of nitrification and urease inhibitors (NUI) in conjunction with nitrogen (N) fertilizers improves the efficiency of N fertilizers. However, NUI are frequently found in surface waters through leaching or surface runoff. Bank filtration (BF) is considered as a low-cost water treatment system providing high quality water by efficiently removing large amounts of organic micropollutants from surface water. The fate of NUI in managed aquifer recharge systems such as BF is poorly known. The aim of this work was to investigate sorption and degradation of NUI in simulated BF under near-natural conditions. Besides, the effect of NUI on the microbial biomass of slowly growing microorganisms and the role of microbial biomass on NUI removal was investigated. Duplicate sand columns (length 1.7 m) fed with surface water were spiked with a pulse consisting of four nitrification (1,2,4-triazole, dicyanodiamide, 3,4-dimethylpyrazole and 3-methylpyrazole) and two urease inhibitors (n-butyl-thiophosphoric acid triamide and n-(2-nitrophenyl) phosphoric triamide). The average spiking concentration of each NUI was 5 μg/L. Experimental and modeled breakthrough curves of NUI indicated no retardation for any of the inhibitors. Therefore, biodegradation was identified as the main elimination pathway for all substances and was highest in zones of high microbial biomass. Removal of 1,2,4-triazole was 50% and n-butyl-thiophosphoric acid triamide proved to be highly degradable and was completely removed after a hydraulic retention time (HRT) of 24 h. 50% of the mass recovery for nitrification inhibitors except for 3,4-dimethylpyrazole was observed at the effluent (4 days HRT). In addition, a mild effect of NUI on microbial biomass was noted. This study highlights that the degradation of NUI in BF depends on HRT and microbial biomass.

Biochar decreases and nitrification inhibitor increases phosphorus limitation for microbial growth in a wheat-canola rotation

Agricultural management practices affect microbial populations and ecoenzymatic activities; however, the effect of these practices on ecological stoichiometry relating the elemental ratio of resources to microbial biomass is poorly understood. In a 2-year field study, we assessed the effects of biochar and nitrapyrin (a commonly used nitrification inhibitor (NI)) on the ecological stoichiometry and microbial nutrient limitation in a wheat (Triticum aestivum L.)-canola (Brassica juncea L.) rotation. This study used a 3 × 2 factorial design that included two treatments: (i) biochar with three levels: no biochar addition (BC0), and biochar added at 10 (BC10) and 20 t ha^-1 (BC20), and (ii) NI with two levels: without (NI0) and with NI (NI1). Soil microbial biomass carbon (C), nitrogen (N) and phosphorus (P) were increased by biochar application, regardless of the application rate, but were not affected by NI application. Biochar increased and NI decreased β-1,4-glucosidase, β-1,4-N-acetyl glucosaminidase and acid phosphatase (P < 0.05) with subsequent changes in ecoenzymatic stoichiometry. Ecoenzymatic stoichiometry analysis showed microbial P limitation relative to N in the studied area irrespective of the treatment, with contrasting effects of biochar (decreasing) and NI (increasing) on the vector angle of ecoenzymatic stoichiometry (P = 0.037 and 0.043, respectively). Biochar applied at 20 t ha^-1 decreased the threshold elemental ratio of C:P at which microbial growth switches between nutrient and C limitations, suggesting a shift towards C relative to nutrient (P) limitation. This study concludes that biochar produced from manure compost can be useful in increasing microbial growth by alleviating P limitations in a wheat-canola rotation.

Biochar decreases the efficacy of the nitrification inhibitor nitrapyrin in mitigating nitrous oxide emissions at different soil moisture levels

Unprecedented increases in agricultural nitrous oxide (N₂O) emissions in recent years have caused substantial environmental pollution that leads to ozone depletion and global warming. Application of biochar and/or nitrification inhibitors (NIs) has the potential to reduce N₂O emissions; however, it is not clear how biochar application may affect the efficacy of NI in reducing nitrification rates, soil enzyme activities, and N₂O emissions under different soil moisture regimes. We conducted a 60-day laboratory incubation experiment to study the effects of manure biochar and nitrapyrin (as a NI) on N₂O emissions from a urea fertilized soil with either 60 (low) or 80% (high) water-filled pore space (WFPS). Nitrification rates were significantly affected by biochar × NI × WFPS and biochar × WFPS interactions. Biochar initially increased and then decreased the rates, resulting in 45.2 and 26.6% (P < 0.001 for both) overall reductions in low and high WFPS, respectively while NI reduced the rates only in the first 10 days at 60% WFPS. Biochar decreased (P < 0.001) and NI increased (P = 0.007) β-1,4-N-acetyl glucosaminidase activities while urease activities were increased (P < 0.001) by biochar across WFPS. Biochar had significant interaction with NI in cumulative N₂O emissions with the efficacy of NI being reduced when co-applied with biochar. Cumulative N₂O emissions were greater at high than at low WFPS; the emissions were decreased by biochar at 60% WFPS and NI at both 60 and 80% WFPS. We conclude that biochar reduces efficacy of nitrapyrin in mitigating N₂O emissions and their effects on net nitrification rates, enzyme activities and N₂O emissions are dependent on soil moisture level.

The Role of Biochar in Regulating the Carbon, Phosphorus, and Nitrogen Cycles Exemplified by Soil Systems

Biochar is a carbon-rich material prepared from the pyrolysis of biomass under various conditions. Recently, biochar drew great attention due to its promising potential in climate change mitigation, soil amendment, and environmental control. Obviously, biochar can be a beneficial soil amendment in several ways including preventing nutrients loss due to leaching, increasing N and P mineralization, and enabling the microbial mediation of N2O and CO2 emissions. However, there are also conflicting reports on biochar effects, such as water logging and weathering induced change of surface properties that ultimately affects microbial growth and soil fertility. Despite the voluminous reports on soil and biochar properties, few studies have systematically addressed the effects of biochar on the sequestration of carbon, nitrogen, and phosphorus in soils. Information on microbially-mediated transformation of carbon (C), nitrogen (N), and phosphorus (P) species in the soil environment remains relatively uncertain. A systematic documentation of how biochar influences the fate and transport of carbon, phosphorus, and nitrogen in soil is crucial to promoting biochar applications toward environmental sustainability. This report first provides an overview on the adsorption of carbon, phosphorus, and nitrogen species on biochar, particularly in soil systems. Then, the biochar-mediated transformation of organic species, and the transport of carbon, nitrogen, and phosphorus in soil systems are discussed. This review also reports on the weathering process of biochar and implications in the soil environment. Lastly, the current knowledge gaps and priority research directions for the biochar-amended systems in the future are assessed. This review focuses on literatures published in the past decade (2009–2021) on the adsorption, degradation, transport, weathering, and transformation of C, N, and P species in soil systems with respect to biochar applications.

Gross Ammonification and Nitrification Rates in Soil Amended with Natural and NH4-Enriched Chabazite Zeolite and Nitrification Inhibitor DMPP

Using zeolite-rich tuffs for improving soil properties and crop N-use efficiency is becoming popular. However, the mechanistic understanding of their influence on soil N-processes is still poor. This paper aims to shed new light on how natural and NH4+-enriched chabazite zeolites alter short-term N-ammonification and nitrification rates with and without the use of nitrification inhibitor (DMPP). We employed the 15N pool dilution technique to determine short-term gross rates of ammonification and nitrification in a silty-clay soil amended with two typologies of chabazite-rich tuff: (1) at natural state and (2) enriched with NH4+-N from an animal slurry. Archaeal and bacterial amoA, nirS and nosZ genes, N2O-N and CO2-C emissions were also evaluated. The results showed modest short-term effects of chabazite at natural state only on nitrate production rates, which was slightly delayed compared to the unamended soil. On the other hand, the addition of NH4+-enriched chabazite stimulated NH4+-N production, N2O-N emissions, but reduced NO3−-N production and abundance of nirS-nosZ genes. DMPP efficiency in reducing nitrification rates was dependent on N addition but not affected by the two typologies of zeolites tested. The outcomes of this study indicated the good compatibility of both natural and NH4+-enriched chabazite zeolite with DMPP. In particular, the application of NH4+-enriched zeolites with DMPP is recommended to mitigate short-term N losses.

Co-application of high temperature biochar with 3,4-dimethylpyrazole-phosphate treated ammonium sulphate improves nitrogen use efficiency in maize

This study aimed on the increasing nitrogen use efficiency (NUE) of maize via the use of high temperature produced biochar (700 °C). Maize was grown to maturity on two contrasting soils (acidic Cambisol and neutral Chernozem) in pots with a treatment of biochar co-applied with ammonium sulphate stabilised by a nitrification inhibitor (3,4-dimethylpyrazole-phosphate, DMPP) or un-stabilised. The combination of biochar with ammonium sulphate containing DMPP increased maize biomass yield up to 14%, N uptake up to 34% and NUE up to 13.7% compared to the sole application of ammonium sulphate containing DMPP. However, the combination of biochar with un-stabilised ammonium sulphate (without DMPP) had a soil-specific influence and increased maize biomass only by 3.8%, N uptake by 27% and NUE by 11% only in acidic Cambisol. Further, the biochar was able to increase the uptake of phosphorus (P) and potassium (K) in both stabilised and un-stabilised treatments of ammonium sulphate. Generally, this study demonstrated a superior effect from the combined application of biochar with ammonium sulphate containing DMPP, which improved NUE, uptake of P, K and increased maize biomass yield. Such a combination may lead to higher efficiency of fertilisation practices and reduce the amount of N fertiliser to be applied.

The mechanisms of biochar interactions with microorganisms in soil

Biochar, a carbonaceous material, is increasingly used in the remediation of the anthropogenically polluted soils and the restoration of their ecological functions. However, the interaction mechanisms among biochar, inorganic and organic soil properties and soil biota are still not very clear. The effect of biochar on soil microorganisms is very diverse. Several mechanisms of these interactions were suggested. However, a well acceptable mechanism of biochar effect on soil microorganisms is still missing. Therefore, efforts were made to examine and proposed a mechanism of the interactions between biochar and microorganisms, as well as existing problems of biochar impacts on main groups of soil enzymes, the composition of the microbiota and the detoxification (heavy metals) and degradation (polycyclic aromatic hydrocarbons) of soil pollutants. The data on the process of biochar colonization by microorganisms and the effect of volatile pyrolysis products released by biochar on the soil microbiota were analysed in detail. The effects of biochar on the physico-chemical properties of soils, the content of mineral nutrients and the response of microbial communities to these changes are also discussed. The information provided here may contribute to the solution of the feasibility, effectiveness and safety of the biochar questions to enhance the soil fertility and to detoxify pollutants in soils.

Urease and Nitrification Inhibitors—As Mitigation Tools for Greenhouse Gas Emissions in Sustainable Dairy Systems: A Review

Currently, nitrogen fertilizers are utilized to meet 48% of the total global food demand. The demand for nitrogen fertilizers is expected to grow as global populations continue to rise. The use of nitrogen fertilizers is associated with many negative environmental impacts and is a key source of greenhouse and harmful gas emissions. In recent years, urease and nitrification inhibitors have emerged as mitigation tools that are presently utilized in agriculture to prevent nitrogen losses and reduce greenhouse and harmful gas emissions that are associated with the use of nitrogen-based fertilizers. Both classes of inhibitor work by different mechanisms and have different physiochemical properties. Consequently, each class must be evaluated on its own merits. Although there are many benefits associated with the use of these inhibitors, little is known about their potential to enter the food chain, an event that may pose challenges to food safety. This phenomenon was highlighted when the nitrification inhibitor dicyandiamide was found as a residual contaminant in milk products in 2013. This comprehensive review aims to discuss the uses of inhibitor technologies in agriculture and their possible impacts on dairy product safety and quality, highlighting areas of concern with regards to the introduction of these inhibitor technologies into the dairy supply chain. Furthermore, this review discusses the benefits and challenges of inhibitor usage with a focus on EU regulations, as well as associated health concerns, chemical behavior, and analytical detection methods for these compounds within milk and environmental matrices.

Biochar counteracts nitrification inhibitor DMPP-mediated negative effect on spinach (Spinacia oleracea L.) growth

The use of nitrification inhibitors (NIs) such as 3,4-dimethylpyrazole phosphate (DMPP) has been suggested to diminish agricultural soil nitrate (NO₃^-) loss and increase nitrogen (N) use efficiency (NUE). However, the yield of ammonium (NH₄⁺)-sensitive plants such as spinach (Spinacia oleracea L.) may be adversely affected by the application of NIs at high N levels and, on the other hand, the efficiency of the NIs may also be affected by soil amendments such as biochar. These two issues are still not adequately addressed. The aim of this study was to evaluate the effect of different N levels including DMPP or not in a calcareous soil with and without amendment of wheat straw biochar on spinach yield, NUE, nitrate concentration of spinach leaf, activity of enzymes nitrate reductase (NR) and nitrite reductase (NiR), and soil ammonium (NH₄⁺) and NO₃^- concentration under greenhouse conditions. This experiment was carried out with different N rates factor at seven levels (un-fertilized, N0; fertilized with 50 mg N kg^-1 soil, N50; fertilized with 75 mg N kg^-1 soil, N75; fertilized with 100 mg N kg^-1 soil, N100; fertilized with N50 + DMPP; fertilized with N75 + DMPP; and fertilized with N100 + DMPP) and biochar (BC) factor at two levels (0, 0%BC; and 2% (w/w), 2%BC) with six replications over a 56-day cultivation period of spinach. Results showed that the application of DMPP had no significant effect on the yield of spinach plant at low and medium levels of N (50 and 75 mg N kg^-1 soil), but decreased the yield of this plant at the higher level of N (100 mg N kg^-1 soil). However, application of BC decreased the negative effect of DMPP on spinach yield as the yield in spinach plants fertilized with N75 + DMPP and N100 + DMPP significantly increased. Both application of DMPP and addition of BC to soil decreased leaf NO₃^- concentration by 29.2% and 16.3% compared to control, respectively. Biochar compared to control decreased NR activity by 46.3%. With increasing N rate, NR and NiR activities increased, but DMPP decreased the activities of both enzymes. Biochar reduced the efficiency of DMPP as soil NH₄⁺ concentration was higher in the treatments containing DMPP without BC at 56 days after planting. Biochar and DMPP could increase the quality of spinach plant through decreasing the leaf NO₃^- concentration. In general, wheat straw biochar counteracted DMPP-mediated negative effect on growth of spinach plant at high level of N by decreasing the efficiency of this inhibitor. These results provide the useful information for managing the application rate of N fertilizers including DMPP in biochar-amended soil.

Effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N-turnover, the N2O reductase-gene nosZ and N2O:N2 partitioning from agricultural soils

Nitrification inhibitors (NIs) have been shown to reduce emissions of the greenhouse gas nitrous oxide (N₂O) from agricultural soils. However, their N₂O reduction efficacy varies widely across different agro-ecosystems, and underlying mechanisms remain poorly understood. To investigate effects of the NI 3,4-dimethylpyrazole-phosphate (DMPP) on N-turnover from a pasture and a horticultural soil, we combined the quantification of N₂ and N₂O emissions with ¹⁵N tracing analysis and the quantification of the N₂O-reductase gene (nosZ) in a soil microcosm study. Nitrogen fertilization suppressed nosZ abundance in both soils, showing that high nitrate availability and the preferential reduction of nitrate over N₂O is responsible for large pulses of N₂O after the fertilization of agricultural soils. DMPP attenuated this effect only in the horticultural soil, reducing nitrification while increasing nosZ abundance. DMPP reduced N₂O emissions from the horticultural soil by >50% but did not affect overall N₂ + N₂O losses, demonstrating the shift in the N₂O:N₂ ratio towards N₂ as a key mechanism of N₂O mitigation by NIs. Under non-limiting NO₃⁻ availability, the efficacy of NIs to mitigate N₂O emissions therefore depends on their ability to reduce the suppression of the N₂O reductase by high NO₃⁻ concentrations in the soil, enabling complete denitrification to N₂.

Reduction of N2O emission by biochar and/or 3,4-dimethylpyrazole phosphate (DMPP) is closely linked to soil ammonia oxidizing bacteria and nosZI-N2O reducer populations

Biochar has been demonstrated to reduce nitrous oxide (N₂O) emissions from soils, but its effect is highly soil-dependent. In particular, in soils with strong nitrification potential, biochar addition may increase N₂O emissions. Thus, in soils with strong nitrification potential, the combination of biochar with the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) may be more effective in reducing N₂O emissions than biochar alone. However, the combined use of biochar and DMPP on soil N₂O emissions is relatively unexplored, and underlying microbial mechanisms of how biochar and/or DMPP amendment affect N₂O emissions is still largely unknown. Here, a 30-day incubation experiment was established with four treatments: CK (control), BC (biochar), DMPP, and BD (biochar and DMPP), all at agronomically recommended rates, and N cycling assessed following addition of urea. Treatment of soil with BC, DMPP and BD reduced N₂O emissions (compared with urea alone) by 59.1%, 95.5% and 74.1%, respectively. Quantification of N cycling genes (amoA, nirS, nirK, and nosZ) indicated that biochar stimulated growth of ammonia oxidizing archaea (AOA) and bacteria (AOB), while DMPP alone inhibited the activity and growth of AOB. In the BD treatment, DMPP was absorbed onto biochar reducing its efficacy in inhibiting AOB growth. The response patterns of nirS/nirK nitrite-reducing denitrifiers to biochar and/or DMPP addition varied among clades. Notably, biochar and/or DMPP increased the abundance of nosZI and nosZII-N₂O reducers, but nosZI-clade taxa were more closely associated with reducing N₂O emission than nosZII taxa. Overall, our findings proved that the dynamics of AOB and nosZI-N₂O reducers resulting from the addition of biochar and/or DMPP played a key role in governing soil N₂O emissions.

Biochar reduces the efficiency of nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) mitigating N2O emissions

Among strategies suggested to decrease agricultural soil N₂O losses, the use of nitrification inhibitors such as DMPP (3,4-dimethylpyrazole phosphate) has been proposed. However, the efficiency of DMPP might be affected by soil amendments, such as biochar, which has been shown to reduce N₂O emissions. This study evaluated the synergic effect of a woody biochar applied with DMPP on soil N₂O emissions. A incubation study was conducted with a silt loam soil and a biochar obtained from Pinus taeda at 500 °C. Two biochar rates (0 and 2% (w/w)) and three different nitrogen treatments (unfertilized, fertilized and fertilized + DMPP) were assayed under two contrasting soil water content levels (40% and 80% of water filled pore space (WFPS)) over a 163 day incubation period. Results showed that DMPP reduced N₂O emissions by reducing ammonia-oxidizing bacteria (AOB) populations and promoting the last step of denitrification (measured by the ratio nosZI + nosZII/nirS + nirK genes). Biochar mitigated N₂O emissions only at 40% WFPS due to a reduction in AOB population. However, when DMPP was applied to the biochar amended soil, a counteracting effect was observed, since the N₂O mitigation induced by DMPP was lower than in control soil, demonstrating that this biochar diminishes the efficiency of the DMPP both at low and high soil water contents.

Environmentally persistent free radicals and particulate emissions from the thermal degradation of Croton megalocarpus biodiesel

Pyrolysis of biodiesel at high temperatures may result in the formation of transient and stable free radicals immobilized on particulate emissions. Consequently, free radicals adsorbed on particulates are believed to be precursors for health-related illnesses such as cancer, cardiac arrest, and oxidative stress. This study explores the nature of free radicals and particulate emissions generated when Croton megalocarpus biodiesel is pyrolyzed at 600 °C in an inert environment of flowing nitrogen at a residence time of 0.5 s at 1 atm. The surface morphology of thermal emissions were imaged using a field emission gun scanning electron microscope (FEG SEM) while the radical characteristics were investigated using an electron paramagnetic resonance spectrometer (EPR). A g-value of 2.0024 associated with a narrow ∆Hp-p of 3.65 G was determined. The decay rate constant for the radicals was low (1.86 × 10^-8 s^-1) while the half-life was long ≈ 431 days. The observed EPR characterization of Croton megalocarpus thermal particulates revealed the existence of free radicals typical of those found in coal. The low g-value and low decay rate constant suggests that the free radicals in particulates are possibly carbon-centered. The mechanistic channel for the formation of croton char from model biodiesel component (9-dodecenoic acid, methyl ester) has been proposed in this study.