Global impact of enhanced-efficiency fertilizers on vegetable productivity and reactive nitrogen losses

Vegetables are the most consumed non-staple food globally, and their production is crucial for dietary diversity and public health. Use of enhanced-efficiency fertilizers (EEFs) in vegetable production could improve vegetable yield and quality while reducing reactive nitrogen (Nr) losses. However, different management and environmental factors has significantly distinctive impacts on the effectiveness of EEFs. In this study, a worldwide meta-analysis based on the data collected from 144 studies was performed to assess the impacts of EEF (nitrification inhibitor [NI] and polymer-coated urea [PCU]) application on vegetable yield, nitrogen (N) uptake, nitrogen use efficiency (NUE), vegetable quality and Nr losses (nitrous oxide [N2O] emissions, ammonia [NH3] volatilization, and nitrate [NO3-] leaching). The effects of the applied EEFs on vegetable yields and N2O emissions were assessed with different management practices (cultivation system, vegetable type and N application rate) and environmental conditions (climatic conditions and soil properties). Compared to conventional fertilizers, EEFs significantly improved vegetable yield (7.5-8.1 %) and quality (vitamin C increased by 10.7-13.6 %, soluble sugar increased by 9.3-10.9 %, and nitrate content reduced by 17.2-25.1 %). Meanwhile, the application of EEFs demonstrated a great potential for Nr loss reduction (N2O emissions reduced by 40.5 %, NO3- leaching reduced by 45.8 %) without compromising vegetable yield. The NI was most effective in reducing N2O emissions (40.5 %), but it significantly increased NH3 volatilization (32.4 %). While PCU not only significantly reduced N2O emissions (24.4 %) and NO3- leaching (28.7 %), but also significantly reduced NH3 volatilization (74.5 %). And N application rate, soil pH, and soil organic carbon (SOC) were the main factors affecting the yield and environmental effects of EEFs. Moreover, the yield-enhancing effect of NI and PCU were better at low soil N availability and SOC, respectively. Thus, it is important to adopt the appropriate EEF application strategy targeting specific environmental conditions and implement it at the optimal N application rate.

Partial substitution of manure increases N2O emissions in the alkaline soil but not acidic soils

The fertilization regimes of combining manure with synthetic fertilizer are benefits for crop yields and soil fertility in cropping systems as compared to sole synthetic fertilization, but the responses of nitrous oxide (N2O) emissions to these practices are inconsistent in the literatures. We hypothesized that it is caused by different proportions of nitrogen (N) applied as manure and various soil properties. Here, we conducted a microcosm experiment, and measured the N2O emissions from control (no N) and five manure substitution treatments (supplied 100 mg N kg-1 using the combination of urea with manure) with a range of proportions of N applied as manure (0, 25%, 50%, 75%, and 100%) in three different soil types (fluvo-aquic soil, black soil, and latosol) under aerobic condition. The stimulated effect on N2O emissions was more pronounced after manure application in an alkaline soil with high nitrification rate, due to relatively rapid soil DOC depletion and N mineralization of manure. N2O emissions from partial substitution of urea with manure were significantly higher than manure-only addition under high soil pH due to abundant labile C from manure. However, there was no difference between manure substitution treatments under acid soils. Nitrification inhibitor substantially decreased N2O emissions with increasing soil pH, but it was less effective in mitigating N2O emissions with larger proportion of manure. This is likely due to the slow nitrification under low soil pH, and denitrification derived N2O increased with increasing manure application rate. Collectively, our study shows that the application of manure substitution to alkaline soils requires careful consideration, which might have rapid nitrification potential and hence trigger significant N2O emissions. The knowledge gained in this work will help the decision-makers in optimizing a sound N fertilization regime interacted with soil properties for sustainable crop production and N2O mitigation.

Global warming potential assessment under reclaimed water and livestock wastewater irrigation coupled with co-application of inhibitors and biochar

The application of nitrification inhibitors (nitrapyrin) and urease inhibitors (N-(N-butyl) thiophosphoric triamide) under conventional water resources has been considered as an effective means to improve nitrogen utilization efficiency and mitigate soil greenhouse gas emissions. However, it is not known whether the inhibitors still have an inhibitory effect under unconventional water resources (reclaimed water and livestock wastewater) irrigation and whether their use in combination with biochar improves the mitigation effect. Therefore, unconventional water resources were used for irrigation, with groundwater (GW) control. Nitrapyrin and N-(N-butyl) thiophosphoric triamide were used alone or in combination with biochar in a pot experiment, and CO2, N2O, and CH4 emissions were measured. The results showed that irrigation of unconventional water resources exacerbated global warming potential (GWP). All exogenous substance treatments increased CO2 and CH4 emissions and suppressed N2O emissions, independent of the type of water, compared to no substances (NS). The inhibitors were ineffective in reducing the GWP whether or not in combination with biochar, and the combined application of inhibitors with biochar further increased the GWP. This study suggests that using inhibitors and biochar in combination to regulate the greenhouse effect under unconventional water resources irrigation should be done with caution.

Digestate induces significantly higher N2O emission compared to urea under different soil properties and moisture

Digestate is considered as an option for recycling resources and a part of the substitution for chemical fertilizers to reduce environmental impacts. However, its application may lead to significant nitrous oxide (N2O) emissions because of its high concentration of ammonium and degradable carbon. The research objectives are to evaluate how N2O emissions respond to digestate as compared to urea application and whether this depends on soil properties and moisture. Either digestate or urea (100 mg N kg-1) was applied with and without a nitrification inhibitor of 3,4-dimethylpyrazole phosphate (DMPP) to three soil types (fluvo-aquic soil, black soil, and latosol) under three different soil moisture conditions (45, 65, and 85% water-filled pore space (WFPS)) through microcosm incubations. Results showed that digestate- and urea-induced N2O emissions increased exponentially with soil moisture in the three studied soils, and the magnitude of the increase was much greater in the alkaline fluvo-aquic soil, coinciding with high net nitrification rate and transient nitrite accumulation. Compared with urea-amended soils, digestate led to significantly higher peaks in N2O and carbon dioxide (CO2) emissions, which might be due to stimulated rapid oxygen consumption and mineralized N supply. Digestate-induced N2O emissions were all more than one time higher than those induced by urea at the three moisture levels in the three studied soils, except at 85% WFPS in the fluvo-aquic soil. DMPP was more effective at mitigating N2O emissions (inhibitory efficacy: 73%-99%) in wetter digestate-fertilized soils. Overall, our study shows the contrasting effect of digestate to urea on N2O emissions under different soil properties and moisture levels. This is of particular value for determining the optimum of applying digestate under varying soil moisture conditions to minimize stimulated N2O emissions in specific soil properties.

Nitrite stimulates HONO and NOx but not N2O emissions in Chinese agricultural soils during nitrification

The long-lived greenhouse gas nitrous oxide (N2O) and short-lived reactive nitrogen (Nr) gases such as ammonia (NH3), nitrous acid (HONO), and nitrogen oxides (NOx) are produced and emitted from fertilized soils and play a critical role for climate warming and air quality. However, only few studies have quantified the production and emission potentials for long- and short-lived gaseous nitrogen (N) species simultaneously in agricultural soils. To link the gaseous N species to intermediate N compounds [ammonium (NH4+), hydroxylamine (NH2OH), and nitrite (NO2-)] and estimate their temperature change potential, ex-situ dry-out experiments were conducted with three Chinese agricultural soils. We found that HONO and NOx (NO + NO2) emissions mainly depend on NO2-, while NH3 and N2O emissions are stimulated by NH4+ and NH2OH, respectively. Addition of 3,4-dimethylpyrazole phosphate (DMPP) and acetylene significantly reduced HONO and NOx emissions, while NH3 emissions were significantly enhanced in an alkaline Fluvo-aquic soil. These results suggested that ammonia-oxidizing bacteria (AOB) and complete ammonia-oxidizing bacteria (comammox Nitrospira) dominate HONO and NOx emissions in the alkaline Fluvo-aquic soil, while ammonia-oxidizing archaea (AOA) are dominant in the acidic Mollisol. DMPP effectively mitigated the warming effect in the Fluvo-aquic soil and the Ultisol. In conclusion, our findings highlight NO2- significantly stimulates HONO and NOx emissions from dryland agricultural soils, dominated by nitrification. In addition, subtle differences of soil NH3, N2O, HONO, and NOx emissions indicated different N turnover processes, and should be considered in biogeochemical and atmospheric chemistry models.

Study on the mechanism of nitrapyrin microcapsule suspension effectively improving nitrification inhibition rate in black soil

Nitrification inhibitors (NIs) have been widely applied to inhibit nitrification and reduce N2O emissions in agriculture. However, there are still some shortcomings, e.g. short effective periods, large applying amounts, low effectiveness, easy deactivation and different effect. Thus, a nitrapyrin microcapsule suspension (CPCS) was used as a new experimental material to elaborate its effects on nitrogen transformation and microbial response mechanisms in black soil by cultivation experiments with six treatments of no fertilization (CK), urea, urea+ 0.2 % CPES, urea+ 0.1 % CPCS, urea+ 0.2 % CPCS, and urea+ 0.3 % CPCS. The content of ammonium, nitrate nitrogen, functional microbial activity, degradation rate and adsorption characteristics of CPCS in the soil at different incubating times were determine. Compared with the nitrapyrin emulsifiable concentrate (CPEC) treatment, the degradation rate of CPCS decreased by 21.54 %, the half-life increased by 10.2 days, and the adsorption rate of nitrapyrin on black soil decreased more than 6-fold. CPCS effectively inhibited the transformation of ammonium nitrogen to nitrate nitrogen within more than 42 days. CPCS had a negative effect on amoA gene abundance and a positive effect on nrfA gene abundance. The research results provide a basic theoretical support for the application of CPCS on black soil.

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.

Legume cover with optimal nitrogen management and nitrification inhibitor enhanced net ecosystem economic benefits of peach orchard

Peach (Prunus persica L.), as a traditional kind of fruits in China, was extremely dependent on large application of nitrogen (N) fertilizer to maintain high fruit yield and commercial income, resulting in raising environmental damage risk. Therefore, a three-year field trail was conducted to clarify the environmental N loss under conventional management, investigate the positive effects of optimal N management, legume cover and 3,4-dimethylpyrazole phosphate (DMPP) on N input/output and the net ecosystem economic benefits (NEEB). There are four treatments in this study: conventional fertilizer management with 521.1 kg N ha-1 yr-1 input (CU); optimal N management including 406.4 kg N ha-1 yr-1 input and deep fertilization (OP); DMPP was added to OP at rate of 1 % (w/w) (OPD); legume (white clover) was covered to OPD (OPDG). Results showed 102.9 kg N ha-1 was removed by annual fruit and residues (including pruned branches, pruned and fallen leaves), while 70.2 kg N ha-1 was lost to the environment by ammonia (NH3), nitrous oxide (N2O) and N runoff loss under the conventional fertilizer management. While, the optimal N management mitigated NH3 volatilization about 49.3 %, further added DMPP abated N2O emission by 61.4 %, besides covered white clover lowered N runoff loss by 64.5 %. The NEEB results revealed that optimal N management combined with added DMPP and covered white clover could minimize the production cost, reduce environmental damage cost by 35.9 %, increase fruit yield by 10.3 % and achieved the maximum NEEB with improvement of 27.1 %, in comparison of the conventional fertilizer management. Generally, conventional peach cultivation constituted overwhelming N loss to raise potential environmental risk. While, extending mode of optimized N management combined with DMPP and legume cover could not only realize high fruit revenue, but also abate environmental N losses, thereby should be considered as effective strategy for sustainable fruit cropping systems.

Niche Differentiation Among Canonical Nitrifiers and N2O Reducers Is Linked to Varying Effects of Nitrification Inhibitors DCD and DMPP in Two Arable Soils

The efficacy of nitrification inhibitors (NIs) dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) varies with soil types. Understanding the microbial mechanisms for this variation may lead to better modelling of NI efficacy and therefore on-farm adoption. This study addressed the response patterns of mineral nitrogen, nitrous oxide (N₂O) emission, abundances of N-cycling functional guilds and soil microbiota characteristics, in relation to urea application with or without DCD or DMPP in two arable soils (an alkaline and an acid soil). The inhibition of nitrification rate and N₂O emission by NI application occurred by suppressing ammonia-oxidizing bacteria (AOB) abundances and increasing the abundances of nosZI-N₂O reducers; however, abundances of ammonia-oxidizing archaea (AOA) were also stimulated with NIs-added in these two arable soils. DMPP generally had stronger inhibition efficiency than DCD, and both NIs' addition decreased Nitrobacter, while increased Nitrospira abundance only in alkaline soil. N₂O emissions were positively correlated with AOB and negatively correlated with nosZI in both soils and AOA only in acid soil. Moreover, N₂O emissions were also positively correlated with nirK-type denitrifiers in alkaline soil, and clade A comammox in acid soil. Amendment with DCD or DMPP altered soil microbiota community structure, but had minor effect on community composition. These results highlight a crucial role of the niche differentiation among canonical ammonia oxidizers (AOA/AOB), Nitrobacter and Nitrospira, as well as nosZI- and nosZII-N₂O reducers in determining the varying efficacies of DCD and DMPP in different arable soils.

Evaluation of a crop rotation with biological inhibition potential to avoid N2O emissions in comparison with synthetic nitrification inhibition

Agriculture has increased the release of reactive nitrogen to the environment due to crops' low nitrogen-use efficiency (NUE) after the application of nitrogen-fertilisers. Practices like the use of stabilized-fertilisers with nitrification inhibitors such as DMPP (3,4-dimethylpyrazole phosphate) have been adopted to reduce nitrogen losses. Otherwise, cover crops can be used in crop-rotation-strategies to reduce soil nitrogen pollution and benefit the following culture. Sorghum (Sorghum bicolor) could be a good candidate as it is drought tolerant and its culture can reduce nitrogen losses derived from nitrification because it exudates biological nitrification inhibitors (BNIs). This work aimed to evaluate the effect of fallow-wheat and sorghum cover crop-wheat rotations on N₂O emissions and the grain yield of winter wheat crop. In addition, the suitability of DMPP addition was also analyzed. The use of sorghum as a cover crop might not be a suitable option to mitigate nitrogen losses in the subsequent crop. Although sorghum-wheat rotation was able to reduce 22% the abundance of amoA, it presented an increment of 77% in cumulative N₂O emissions compared to fallow-wheat rotation, which was probably related to a greater abundance of heterotrophic-denitrification genes. On the other hand, the application of DMPP avoided the growth of ammonia-oxidizing bacteria and maintained the N₂O emissions at the levels of unfertilized-soils in both rotations. As a conclusion, the use of DMPP would be recommendable regardless of the rotation since it maintains NH₄⁺ in the soil for longer and mitigates the impact of the crop residues on nitrogen soil dynamics.

Biochar amendments and climate warming affected nitrification associated N2O and NO production in a vegetable field

Soil nitrification driven by ammonia-oxidizing microorganisms is the most important source of nitrous oxide (N₂O) and nitric oxide (NO). Biochar amendment has been proposed as the most promising measure for combating climate warming; both have the potential to regulate the soil nitrification process. However, the comprehensive impacts of different aged biochars and warming combinations on soil nitrification-related N₂O and NO production are not well understood. Here, 1-octyne and acetylene were used to investigate the relative contributions of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to potential nitrification-mediated N₂O and NO production from the fertilized vegetable soil with different aged biochar amendments and soil temperatures in microcosm incubations. Results demonstrated that AOB dominated nitrification-related N₂O and NO production across biochar additions and climate warming. Biochar amendment did not significantly influence the relative contribution of AOB and AOA to N₂O and NO production. Field-aged biochar markedly reduced N₂O and NO production via inhibiting AOB-amoA gene abundance and AOB-dependent N₂O yield while fresh- and lab-aged biochar produced negligible effects on AOB-dependent N₂O yield. Climate warming significantly increased N₂O production and AOB-dependent N₂O yield but less so on NO production. Notably, the relative contribution of AOB to N₂O production was enhanced by climate warming, whereas AOB-derived NO showed the opposite tendency. Overall, the results revealed that field-aged biochar contributed to mitigating warming-induced increases in N₂O and NO production via inhibiting AOB-amoA gene abundance and AOB-dependent N₂O yield. Our findings provided guidance for mitigating nitrogen oxide emissions in intensively managed vegetable production under the context of biochar amendments and climate warming.

The effect of nitrification inhibitors on the aerobic biodegradation of tetracycline antibiotics in swine wastewater

The aerobic biotreatment process for the dual goals of antibiotic removal and ammonia retainment for the field-return-based treatment of swine wastewater was optimized by adding 2-chloro-6-trichloromethylpyridine (TCMP), commonly used as a nitrogen fertilizer synergist. The results show that the dosage of 5-10 mg/L TCMP daily effectively inhibited nitrification. The COD and tetracycline antibiotics (TCs) in the absence of TCMP was removed by 91% and 76%, and became 87% and 78% with 5 mg/L TCMP and 83% and 70% with 10 mg/L TCMP, respectively. The removal efficiency of four TCs generally followed a decreasing trend of chlortetracycline (CTC) > doxycycline (DC) > tetracycline (TC) > oxytetracycline (OTC). A dosage of 5 mg/L TCMP daily inhibited ammonia nitrification effectively and only slightly affected the removal of conventional organic pollutants and TCs. The contribution of volatilization and hydrolysis to the removal of TCs was negligible. The overall removal efficiency of four TCs in removal pathway experiments was 98%, 94%, 97%, and 96% for OTC, CTC, DC, and TC, of which 69%, 41%, 56%, and 62% was contributed by absorption, and 29%, 53%, 41%, and 34% was contributed by biodegradation, respectively. This study may have significant implications for the proper management of livestock wastewater intended to be used as fertilizers, which aims to reduce the exposure risk of antibiotics and preserve its nutrient value.

Impact of cattle slurry application methods on ammonia losses and grassland nitrogen use efficiency

Optimal manure management is required to ensure efficient nutrient supply to farmland and to avoid adverse environmental impacts. Accordingly, ammonia (NH₃) emissions associated with different slurry application techniques were investigated in grassland trials under different soil and weather conditions across Germany. Cattle slurry was applied in two dressings, early in spring and after the first silage cut, with a target amount of 170 kg N ha^-1. The application treatments comprised: trailing shoe (TS), acidified slurry applied with trailing shoe (TS + A), open slot injection (SI), and slurry treated with a nitrification inhibitor (NI) applied by slot injection (SI + NI). In addition, slurry application techniques were compared with a non-N-fertilized control and a mineral fertilizer treatment (calcium ammonium nitrate, CAN). NH₃ measurements followed each N application event. NH₃ losses were equivalent to 1-39% of total ammoniacal nitrogen (TAN) applied. The average NH₃ mitigation potential of the different slurry application techniques compared to TS was 45.7 ± 7, 21.2 ± 6.2 and 13.7 ± 8.2% for TS + A, SI and SI + NI, respectively. The use of nitrification inhibitor with slot injected slurry did not increase NH₃ losses relative to TS (p > 0.05). Mean apparent N use efficiency was two times higher for CAN (49%) than the slurry treatments (24%) but was comparable between SI + NI and CAN in five out of the eight cases. Our results indicate that mean TAN related NH₃ emissions of tested treatments (3.3, 22.6, 12.2, 17.8 and 19.3% for CAN, TS, TS + A, SI and SI + NI, respectively) were generally lower than described in previous studies. Moreover, the results suggested possible increases in NH₃ mitigation and N use efficiency when cattle slurry is applied with acidification or injection techniques. We found no evidence that NI addition to slot injected slurry, a treatment discussed as a measure to reduce N₂O emission and nitrate leaching, changed NH₃ emission.

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

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

Synergistically mitigating nitric oxide emission by co-applications of biochar and nitrification inhibitor in a tropical agricultural soil

Agricultural soils are the hotspots of nitric oxide (NO) emissions, which are related to atmospheric pollution and greenhouse effect. Biochar application has been recommended as an important countermeasure, however, its mitigation efficiency is limited as biochar, under certain conditions, can stimulate soil nitrification. Therefore, biochar co-applied with nitrification inhibitor could optimize the mitigation potential of biochar. Herein, a laboratory-scale experiment was conducted to investigate the effects of co-application of biochar and nitrification inhibitor on NO emission, nitrogen cycling function and bacterial community in a tropical vegetable soil. Results showed that a single application of biochar or nitrification inhibitor significantly decreased NO emissions, and this mitigation effectiveness was amplified by their co-applications. Soil NO₂^--N intensity, along with abundances of AOB-amoA and nirK were significantly and positively correlated with cumulative NO emissions. The stimulated activity of ammonia monooxygenase and growths of AOB and total comammox Nitrospira by biochar were weakened by nitrification inhibitor, implying decreased nitrification-driven NO production. The nitric oxide reductase activity and related qnorB abundance in nitrification inhibitor-added soils were increased by biochar, indicating promoted NO consumption during denitrification. The nirK abundance and NO₂^--N intensity were decreased more by co-applications of biochar or nitrification inhibitor. Moreover, both biochar and nitrification inhibitor changed bacterial β-diversity, and their co-application synergistically enriched Armatimonadetes and Verrucomicrobia abundances and decreased WPS-2 abundance. This study highlights that co-applications of biochar and nitrification inhibitor can make their respective advantages complementary to each other, thereby achieving a larger mitigation of NO emissions from agricultural soils in tropical regions.

Different effects of the application of urea combined with nitrification inhibitor on cadmium activity in the rice-rape rotation system

Cadmium (Cd) is one of the most harmful and widespread pollutants in agricultural soil, where it is readily taken up by plants and threatens human health through the food chain. Nitrification inhibitors (NIs) are usually used to reduce nitrogen (N) loss in soil and increase the nitrogen use efficiency of crops. However, information regarding the Cd transfer in soil and crops system with the application of urea combined with NIs is limited. Especially, the influences of NIs on Cd availability in the rice-rape rotation are unclear. Here, we studied the pH, N speciation, and Cd activity in soils, as well as Cd accumulation in rice and rapeseed tissues that resulted after the application of dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) under alternating redox conditions. Rice and rape experiments appeared to represent an opposite phenomenon in the treatments of urea + NIs. Addition of NIs increased the pH of paddy soil, but decreased the pH of rapeseed soil. The treatments of urea + DCD and urea + DMPP0.5% produced a significantly lower concentration of extractable Cd in the paddy soil, and reduced the accumulation of Cd in brown rice. For rapeseed, the urea + NI treatments enhanced the Cd activity and increased the accumulation of Cd in rapeseed. It is proposed that NIs could be used to regulate N transformation in agricultural soils and inhibited Cd uptake by rice in urea fertilization. Moreover, the application of NIs combined with urea would potentially favor phytoextraction of Cd by rape, which is a ideal candidate for phytoremediation in Cd-contaminated soil.

The proportion of deposited urine patch intercepted by a delayed inhibitor application

Nitrification inhibitors can reduce nitrous oxide (N₂O) emissions and nitrate leaching losses from agricultural soils. Technologies have been developed to detect and target urine patches for inhibitor application, thereby reducing the total amount of inhibitor used. However, in practice there will be a time delay between the urine deposition and inhibitor application, potentially leading to physical separation of the inhibitor and urine that could reduce the effectiveness of the inhibitor compared to when the inhibitor and urine are well mixed. In this study, 2L of cattle urine was applied on two soil types in New Zealand. Twenty-four hours later the inhibitor dicyandiamide (DCD) was applied. The soil was sampled within 18 h and again after a rainfall event. DCD concentrations were measured in the 0-20 mm, 20-50 mm, and 50-100 mm depth ranges. The movement of the urine in the soil was simulated using the HYDRUS model. Before the rain most of the DCD was within the top 20 mm and intercepted 21-29% of the urine. After the rainfall event the DCD concentration decreased in the 0-20 mm layer and increased in the 20-50 mm layer. 18-55% or 63-79% of the urine was intercepted by DCD at a concentration of >4 ppm using the measured and modelled DCD concentrations, respectively. However, only 0-27% or 0-53% of the urine was intercepted at a DCD concentration >10 ppm.

Optimizing nitrogen management to mitigate gaseous losses and improve net benefits of an open-field Chinese cabbage system

The excessive and inappropriate application of nitrogen (N) fertilizer in open vegetable fields is a major anthropogenic source of gaseous N losses including nitrous oxide (N₂O) and ammonia (NH₃) emissions in China. A 2-yr Chinese cabbage (Brassica pekinensis L.) experiment was carried out to explore the impacts of optimized N management (reduced N application rate, controlled-release urea [CRF] and nitrification inhibitor [NI]) on cabbage yield, soil inorganic N, and N₂O and NH₃ emissions, and to assess their economic benefits by a cost-benefit analysis. Six treatments including i) no N fertilizer (CK), ii) conventional urea fertilizer at 400 kg N ha^-1 based on farmers' practices (CN), iii) conventional urea at 320 kg N ha^-1 (RN), iv) conventional urea (320 kg N ha^-1) with the addition of NI (RN + NI), v) CRF at 320 kg N ha^-1 (CR) and vi) CRF (320 kg N ha^-1) with the addition of NI (CR + NI) were implemented in an open Chinese cabbage field. No significant differences were found in the cabbage yields and soil NH₄⁺-N contents under different N fertilization treatments. Only CR + NI treatment had significantly lower soil NO₃^--N contents than CN by 17.6%-34.6% at the early growing stages of cabbage in both years. Compared with CN, the N₂O emissions were significantly decreased by 8.61%, 34.4%, 37.8% and 46.6% under RN, RN + NI, CR and CR + NI, respectively, indicating that CR + NI favors N₂O abatement especially when NH₃ has been suppressed by other 4 R practices. Meanwhile, the NH₃ volatilization was 20.6% higher under RN + NI and 30.8% and 17.3% lower under CR and CR + NI compared to CN, respectively, which implied that CR was the most effective treatment in reducing the NH₃ volatilization and total gaseous N loss in high NH₃-N loss scenarios. Moreover, the net benefit of RN decreased by $945 USD ha^-1 and those of RN + NI, CR and CR + NI treatments increased by $855, $930 and $1004 USD ha^-1 compared to CN, respectively. This study recommends CR + NI as the optimal N fertilizer management for the sustainable production of vegetables with the lowest environmental risks and the greatest economic benefits.

Effects of water regimes on soil N2O, CH4 and CO2 emissions following addition of dicyandiamide and N fertilizer

Water regimes strongly impact soil C and N cycling and the associated greenhouse gases (GHGs, i.e., CO₂, CH₄ and N₂O). Therefore, a study was conducted to examine the impacts of flooding-drying of soil along with application of nitrogen (N) fertilizer and nitrification inhibitor dicyandiamide (DCD) on GHGs emissions. This study comprised four experimental treatments, including (i) control (CK), (ii) dicyandiamide, 20 mg kg^-1 (DCD), (iii) nitrogen fertilizer, 300 mg kg^-1 (N) and (iv) DCD + N. All experimental treatments were kept under flooded condition at the onset of the experiment, and then converted to 60% water filled pore space (WFPS). At flooding stage, N₂O emissions were lower as compared to 60% WFPS. The highest cumulative N₂O emission was 0.98 mg N₂O-N kg^-1 in N treated soil due to high substrates of mineral N contents, but lowest (0.009 mg N₂O-N kg^-1) in the DCD treatment. The highest cumulative CH₄ emissions (80.54 mg CH₄-C kg^-1) were observed in the N treatment, while uptake of CH₄ was observed in the DCD treatment. As flooded condition converted to 60% WFPS, CO₂ emissions gradually increased in all experimental treatments, but the maximum cumulative CO₂ emission was 477.44 mg kg^-1 in the DCD + N treatment. The maximum dissolved organic carbon (DOC) contents were observed in N and DCD + N treatments with the values of 57.12 and 58.92 mg kg^-1, respectively. Microbial biomass carbon (MBC) contents were higher at flooding while lower at transition phase, and increased at the initiation of 60% WFPS stage. However, MBC contents declined at the later stage of 60% WFPS. The maximum MBC contents were 202.12 and 192.41 mg kg^-1 in N and DCD + N treatments, respectively. Results demonstrated that water regimes exerted a dramatic impact on C and N dynamics, subsequently GHGs, which were highly controlled by DCD at both flooding and 60% WFPS conditions.

Reducing nitrous oxide emissions from irrigated maize by using urea fertilizer in combination with nitrapyrin under different tillage methods

The aim of this study was to evaluate the effectiveness of nitrification inhibitor (nitrapyrin; NI) as a mitigation option for yield-scaled emissions of nitrous oxide (N₂O) under tillage management and urea fertilization in the irrigated maize fields in northern Iran. A split-plot experiment was performed based on a randomized completed blocks design with three replicates. The main plots were the levels of tillage practices (conventional tillage (CT) and minimum tillage (MT), and the subplots were the fertilizer treatments (control, urea, and urea + NI). The gas samples for measuring N₂O emissions were collected during the maize growing season from June to September, using opaque manual circular static chambers. Soil samples were taken at 0-10 cm to determine water-filled pore space, ammonium (NH₄⁺), and nitrate (NO₃^-) concentrations in the soil. When the crop reached physiological maturity, maize was harvested to measure grain yield, biomass production, N uptake of aboveground, and nitrogen use efficiency (NUE). The results showed that the applying NI in combination with urea reduced the total N₂O emissions by up to 58% and 64% in MT and CT, respectively. In the urea + NI treatment, mean soil concentrations of NH₄⁺ and NO₃^- were significantly higher (20%) and lower (23.5%), respectively, compared with other treatments. The NI reduced the yield-scaled N₂O-N emission up to 79% and 55% for CT and MT, respectively. Furthermore, compared to treatment with urea alone, the application of NI increased the NUE of the MT and CT systems by an average of 55% and 46%, respectively. This study emphasized that the application of nitrapyrin should be encouraged in irrigated maize fields, in order to minimize N₂O emissions and improve NUE and biomass production.

Nitrifier denitrification dominates nitrous oxide production in composting and can be inhibited by a bioelectrochemical nitrification inhibitor

Targeted options to reduce nitrous oxide (N₂O) emission from composting is scarce due to challenges in disentangling the complex N₂O production pathways. Here, combined approaches of nitrogen form analysis, isotopocule mapping, quantitative PCR, and Illumina MiSeq sequencing were used to differentiate N₂O production pathways and decipher the underlying biochemical mechanisms. Results suggested that most N₂O was produced at the latter stage through nitrifier denitrification. The bioelectrochemical assistance through applying an electric potential reduced N₂O emissions by 28.5-75.5%, and the underlying mitigation mechanism was ammonia oxidation repression, as evidenced by the observed reduction in the proportion of the amoA containing family Nitrosomonadaceae from 99% to 83% at the lower voltage and to a negligible level at the higher voltage assessed, which was attributed to their depressed competitiveness for oxygen with heterotrophs. The findings provide evidence that the bioelectrochemical assistance could function as a nitrification inhibitor to minimize compost derived N₂O emissions.

Linking soil profile N2O concentration with surface flux in a cotton field under drip fertigation

It remains unclear how the source and rate of nitrogen (N) fertilizers affect N₂O concentration and effluxes along the soil profile under the drip-fertigated agricultural system. A plot-based field study was performed in 2017 and 2018 in a cotton field in arid northwestern China, with an objective to elucidate the impact of the applications of conventional urea (Urea), polymer-coated urea (ESN) and stabilized urea (SuperU) at rates of 120 and 240 kg N ha^-1 on concentration and efflux of N₂O in the soil profile and its relationship with N₂O surface emissions. The in-situ N₂O concentrations at soil depths of 5, 15, 30 and 60 cm were measured and used to estimate soil profile N₂O effluxes. Estimates of surface N₂O flux using the concentration gradient-based (GM) were compared with those measured using the chamber-based (CM) method. In both years, soil N₂O concentrations at all depths increased in response to basal N application at planting or in-season fertigation events. However, N rate or source did not affect soil N₂O concentrations or effluxes at each depth. Surface emissions of N₂O were mostly associated with that presented in the top layer of 0-15 cm. Surface N₂O efflux determined by GM was poorly or not associated with those of chamber measurements, which was attributed to the low N₂O production restricted by soil moisture condition under the drip-fertigated condition. These results highlight the challenge of applying the enhanced efficiency N fertilizer products in the drip-fertigated agricultural system.

Effects of the nitrification inhibitor nitrapyrin and mulch on N2O emission and fertilizer use efficiency using 15N tracing techniques

Nitrous oxide (N₂O), is a potent greenhouse gas (GHG) that shares 7% of global warming around the world. Among different sources, agricultural systems account for approx. 60% of global anthropogenic N₂O emissions. These N₂O emissions are associated with the activity of nitrifiers and denitrifiers that contribute to >4 Tg (teragrams) N₂O-N emission per year. Application of nitrogen (N) fertilizers and manures in agricultural fields plays an imperative role in this regard. On the other hand nitrification inhibitors are an effective approach to minimize N₂O-N emissions from agricultural fields. Here we examined the effects of applying urea with a nitrification inhibitor (Ni) nitrapyrin and mulch (Mu) on urea transformation, nitrous oxide (N₂O) emissions, grain yield and nitrogen (N) uptake efficiency. The treatments include a control (zero N), urea (U) applied at 200 kg N ha^-1, U + Ni (Ni applied at 700 g ha^-1), U+ Mu (Mu applied at 4 t ha^-1) and U + Ni + Mu. The N₂O emission factor (EF) was 66% and 75% when U and Mu were applied, respectively. Yield-scaled N₂O emissions were lower in U and Mu by 45% and 55%, respectively. The Ni coupled with Mu enhanced urea-¹⁵N recovery by 58% and wheat grain yield by 23% and total N uptake by 30% compared with U alone. In conclusion, Ni usage is an effective strategy to mitigate N₂O emissions under field conditions.

The importance of ammonia volatilization in estimating the efficacy of nitrification inhibitors to reduce N2O emissions: A global meta-analysis

Nitrification inhibitors (NIs) have been shown to be an effective tool to mitigate direct N₂O emissions from soils. However, emerging findings suggest that NIs may increase soil ammonia (NH₃) volatilization and, subsequently, indirect N₂O emission. A quantitative synthesis is lacking to evaluate how NIs may affect NH₃ volatilization and the overall N₂O emissions under different environmental conditions. In this meta-analysis, we quantified the responses of NH₃ volatilization to NI application with 234 observations from 89 individual studies and analysed the role of experimental method, soil properties, fertilizer/NI type, fertilizer application rate and land use type as explanatory factors. Furthermore, using data sets where soil NH₃ emission and N₂O emission were measured simultaneously, we re-evaluated the effect of NI on overall N₂O emissions including indirect N₂O emission from NH₃ volatilization. We found that, on average, NIs increased NH₃ volatilization by 35.7% (95% CI: 25.7-46.7%) and increased indirect N₂O emission from NH₃ emission (and subsequent N deposition) by 2.9%-15.2%. Responses of NH₃ volatilization mainly varied with experimental method, soil pH, NI type and fertilizer type. The increase of NH₃ volatilization following NI application showed a positive correlation with soil pH (R² = 0.04, n = 234, P < 0.05) and N fertilizer rate (R² = 0.04, n = 187, P < 0.05). When the indirect N₂O emission was considered, NI's N₂O mitigation effect decreased from 48.0% to 39.7% (EF = 1%), or 28.2% (EF = 5%). The results indicate that using DMPP with ammonium-based fertilizer in low pH, high SOC soils would have a lower risk for increasing NH₃ volatilization than using DCD and nitrapyrin with urea in high pH, lower SOC soil. Furthermore, reducing N application rate may help to improve NIs' overall N₂O emission mitigation efficiency and minimize their impact on NH₃ volatilization.

Use of additives in composting informed by experience from agriculture: Effects of nitrogen fertilizer synergists on gaseous nitrogen emissions and corresponding genes (amoA and nirS)

The effects of two nitrogen fertilizer synergists (urease inhibitor, UI; nitrification inhibitor, NI) on NH₃ and N₂O emissions and the successions of the amoA and nirS genes during composting were assessed. Results showed that the UI and UI + NI treatments reduced NH₃ emissions by 26.3% and 24.3%, respectively, and N₂O emissions were reduced by 63.9% for UI + NI treatment but were not reduced by UI. The addition of UI and NI significantly reduced the abundance of the nirS gene during thermophilic stage, while significantly increased that of the amoA gene during maturation stage. Crenarchaeota was the principal nitrifying archaeal phylum and was significantly affected by pH. Proteobacteria was the main denitrifying bacterial phylum, whose relative abundance was higher for UI + NI treatment than the other treatments. PICRUSt analysis showed that the addition of UI and NI inhibited enzymatic activity related to N transformation during thermophilic stage while enriching enzymatic activity during maturation phase.

Effects of ammonium-based nitrogen addition on soil nitrification and nitrogen gas emissions depend on fertilizer-induced changes in pH in a tea plantation soil

Tea (Camellia sinensis L.) plants have an optimal pH range of 4.5-6.0, and prefer ammonium (NH₄⁺) over nitrate (NO₃^-); strong soil acidification and nitrification are thus detrimental to their growth. Application of NH₄⁺-based fertilizers can enhance nitrification and produce H⁺ that can inhibit nitrification. However, how soil acidification and nitrification are interactively affected by different NH₄⁺-based fertilizers in tea plantations remains unclear. The objective of this research was to evaluate the effect of the application of different forms and rates of NH₄⁺-based fertilizers on pH, net nitrification rates, and N₂O and NO emissions in an acidic tea plantation soil. We conducted a 35-day aerobic incubation experiment using ammonium sulphate, urea and ammonium bicarbonate applied at 0, 100 or 200 mg N kg^-1 soil. Urea and ammonium bicarbonate significantly increased both soil pH and net nitrification rates, while ammonium sulphate did not affect soil pH but reduced net nitrification rates mainly due to the acidic nature of the fertilizer. We found that the effect of different NH₄⁺-based nitrogen on soil nitrification depended on the impact of the fertilizers on soil pH, and nitrification played an important role in NO emissions, but not in N₂O emissions. Overall, urea and ammonium bicarbonate application decoupled crop N preference and the form of N available in spite of increasing soil pH. We thus recommend the co-application of urease and nitrification inhibitors when urea is used as a fertilizer and nitrification inhibitors when ammonium bicarbonate is used as a fertilizer in tea plantations.

Evaluation of N2O emission from rainfed wheat field in northwest agricultural land in China

The net greenhouse gas (NGHG) emissions and net greenhouse gas intensity (NGHGI) were investigated via the determination of nitrous oxide (N₂O) emission in loess soil under rainfed winter wheat monocropping system during 3 years of field study in Northwest China. Five treatments were carried out: control (N₀), conventional nitrogen (N) application (N_Con), optimized N application with straw (SN_Opt), optimized N application with straw and 5% of dicyanodiamide (SN_Opt + DCD), and optimized N rate of slow release fertilizer with straw (SSRF_Opt). Over a 3-year period, the NGHG emissions were achieved 953, 1322, 564, and 1162 kg CO₂-eq ha^-1, simultaneously, and the NGHGI arrived 158, 223, 86, and 191 kg CO₂-eq t^-1 grain in N_Con, SN_Opt, SN_Opt + DCD, and SSR_Opt grain, respectively. Contrasted with conventional farming system, optimized farming methods reduced 32% of N fertilizer use without significant decrease in grain yield, but brought about 38% increase in N₂O emissions, up to 28% gained in soil CH₄ uptake. Thus, it was observed that the straw incorporation performs noticeable increased in N₂O emissions in the winter wheat cropping season. Among the optimized N fertilizer rates compared with the SN_Opt treatment, the SN_Opt +DCD and SSR_Opt treatments decreased in N₂O emissions by approximately 55% and 13%, respectively. Additionally, the N₂O emission factor across over a 3-year period was 0.41 ± 0.08% derived from N fertilizer, and it was half of IPCC default values for upland corps. It is expected possibly due to low precipitation and soil moisture with the monocropping system. The 25% higher in the amount of rainfall (almost 300 mm in 2013-2014) during a cropping season underwent into 1-2-fold increase in N₂O emissions from N-fertilized plots. As the statistical differences among annual cumulative emissions coincided with that during winter wheat growing season, it can be concluded that crop growing season is a vital important period for the determination of N₂O emissions from under rainfed monocropping system.

Ammonia volatilisation from pig slurry and ANS with DMPP applied to Westerwold ryegrass (Lolium multiflorum Lam., cv. Trinova) under Mediterranean conditions

Ammonia volatilisation from agriculture represents an important nitrogen (N) loss which has both environmental and economic impacts. In regions where large amounts of manures are available, there is a need to find appropriate management strategies that help to reuse them without increasing ammonia volatilisation. A study was made of the effect on ammonia volatilisation and yield of fertilising ryegrass with pig slurry (PS) and ammonium nitrosulphate (ANS-26) alone and with the 3,4-dimethylpyrazol phosphate (DMPP) nitrification inhibitor added to them. The study was conducted under Mediterranean conditions at two different sites. The treatments (control, PS, PS + DMPP, ANS-26 and ENTEC®) were established in a randomised block design with three replicates. Ammonia was sampled daily after each fertilisation using semi-static volatilisation chambers. We hypothesised that PS could replace mineral fertiliser without substantially increasing ammonia volatilisation in the studied systems. Temperature positively correlated with ammonia emissions. On the whole, during the two years of the study, the PS treatments presented higher average cumulative ammonia volatilisation (25% of total ammonium nitrogen (TAN) applied at Site 1; 21% of TAN applied at Site 2) than the mineral ones (11% of TAN applied at Site 1; 10% of TAN applied at Site 2). At pre-sowing, ammonia volatilisation was significantly (p < .05) lower (51% at Site 1; 55% at Site 2) than after ryegrass cuts due to burying PS immediately after application. Overall, applying DMPP had no effect on ammonia volatilisation. There were no significant differences in average yield (from 13.7 to 15.8 kg ha^-1 at Site 1; from 11.6 to 13.5 kg ha^-1 at Site 2) between the fertilised treatments, though ENTEC® tended to increase it. Applying PS (pre-sowing fertilisation) in combination with mineral N or processed PS fractions after ryegrass cuts could be an interesting option for the recycling of this livestock by-product without increasing ammonia volatilisation while maintaining yields.

Interactions between dicyandiamide and periphytic biofilms in paddy soils and subsequent effects on nitrogen cycling

Dicyandiamide (DCD) is commonly used as nitrification inhibitors which has the potential to reduce nitrogen loss from paddy soils. In paddy systems, periphytic biofilms are commonly presented at the soil/water interface and show significant effects on nutrient cycling. However, the interaction between DCD and periphytic biofilms in paddy and subsequent effects on nitrogen cycling is unclear. In this work, microcosm experiments were carried out to study the interaction between the periphytic biofilms and DCD and the potential influence on nitrogen cycling from in paddy. Results showed that DCD affected the development of periphytic biofilms, while the presence of periphytic biofilms accelerated DCD degradation. Results also showed DCD application reduced nitrification potential mainly by inhibiting ammonia-oxidizing bacteria (AOB). Higher DCD dosage increased NH₃ volatilization loss. However, presence of periphytic biofilm reduced the NH₃ volatilization loss but increased denitrification. Our work contributes to a better understanding on the nitrogen cycling processes in paddy, and provides useful information for the improvement of nitrogen utilization efficiency and the control of non-point source pollution.

Data on initial leaf P concentrations and final dry matter yields of silage maize in response to row-injected cattle slurry

This article displays a dataset obtained in a field trial conducted in 2016 on a sandy loam and a coarse sandy soil, Denmark. Leaf phosphorus (P) and nitrogen (N) concentrations at the five-leaf stage (V5) and final dry matter (DM) yields of silage maize were determined in response to seven treatments with placed slurry below the maize row. Two row-injection methods combined with slurry acidification or addition of a nitrification inhibitor were tested. Furthermore final crop P uptake and P surplus at field level were determined. This dataset can be used to assess the effect of placed slurry with or without slurry acidification and addition of a nitrification inhibitor on silage maize yields and to enhance our knowledge on maize P uptake and P surpluses at field level. In turn this can support the design of appropriate row-injection machinery of slurry. The data supplied in this article is related to the research article entitled "Row-injected cattle slurry can replace mineral P starter fertiliser and reduce P surpluses without compromising final yields of silage maize" [1], where results from 2017 and 2018 are presented and discussed. The trials in 2016, 2017 and 2018 were conducted on the same study sites. The experimental design in 2017 and 2018 was a full-factorial design and did also include reference treatments with evenly injected slurry, whereas these reference treatments were not included in the present article.

Nitrate leaching and nitrous oxide emissions from maize after grass-clover on a coarse sandy soil: Mitigation potentials of 3,4-dimethylpyrazole phosphate (DMPP)

Cropping of maize (Zea mays L.) on sandy soil in wet climates involves a significant risk for nitrogen (N) losses, since nitrate added in fertilizers or produced from residues and manure may be lost outside the period with active crop N uptake. This one-year lysimeter experiment investigated the potential of Vizura®, a formulation for liquid manure (slurry) with the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP), to mitigate nitrous oxide (N₂O) emissions and nitrate (NO₃^-) leaching from a coarse sandy soil cropped with maize. Maize followed grass-clover (Lolium perenne L.-Trifolium pratense L.) with spring incorporation and was fertilised with cattle slurry. A total of 12 treatments in triplicate were included in a factorial experiment with 1 m² large and 1.4 m deep lysimeters: 1) with or without spraying the above-ground biomass of grass-clover with DMPP before incorporation; 2) application of cattle manure with or without DMPP, or no fertilization; and 3) natural rainfall or extra rain events to represent wet spring conditions, which were simulated with an automated and programmable irrigation system. Around 20 kg N ha^-1 was returned to the soil in grass-clover above-ground biomass, and 145 kg N ha^-1 in cattle manure. Cumulative annual N₂O emissions ranged from 0.4 to 1.3 kg N ha^-1, with between 49 and 86% of emissions occurring during spring. Manure application increased N₂O emissions, while extra rainfall had no effect. The mitigation of N₂O emissions by DMPP ranged from 46 to 67% under natural, and from 44 to 48% under high rainfall conditions. Total annual NO₃^- leaching ranged from 65 to 162 kg N ha^-1. The extent of NO₃^- leaching to 1.4 m depth during spring was low, and instead most (72-83%) of total annual NO₃^--N leaching was recorded during autumn before harvest. The extra rainfall during spring increased NO₃^--N leaching in the pre-harvest period, but it is not clear to what extent this was associated with the N in grass-clover residues or manure applied in spring, or from N mineralisation below the root zone. Despite evidence for a reduction of NO₃^- leaching in three of four scenarios, overall this effect was not significant. No DMPP was detected in leachates. In conclusion, DMPP significantly reduced N₂O emissions from cattle manure on this sandy loam soil independent of rainfall, while there was no significant effect on NO₃^- leaching. The results indicate that N₂O emissions and NO₃^--N leaching were partly derived from below-ground sources of N not affected by DMPP, which should be further investigated to better predict the mitigation potential of nitrification inhibitors.

Modelling of nitrification inhibitor and its effects on emissions of nitrous oxide (N2O) in the UK

Global food demand requires increased uses of fertilizers, leading to nitrous oxide (N₂O) and nitrate leaching due to overuse of fertilizers and poor timing between fertilizer application and plant growth. Using nitrification inhibitors (NIs) can reduce the N₂O emissions but the effectiveness of NIs strongly depend on environmental conditions, and their benefits have been limited due to less than optimal nitrogen rates, timing, quantity, and placement of NIs. Process-based modelling can be helpful in improving the understanding of nitrogen fertilizer with NIs and their effects in different environmental conditions and agricultural practices. But few studies of modelling NIs with application to agricultural soils have been performed. In this paper, we developed a sophisticated biogeochemical reaction process of NIs applied to agricultural soils, which account for the factions of NIs with fertilizer by combining the application rate, soil moisture, and temperature within the DeNitrification DeComposition (DNDC) framework. This model was tested against the data from two agricultural farms in Preston Wynne and Newark in the UK. The results agreed well with the measured data and captured the measured soil moistures and N₂O emissions. In Newark, the average Mean Absolute Error of all blocks is 8.78 and 5.45 for ammonium nitrate or urea respectively while in Preston Wynne, 3.48 and 3.14. The results also showed that the warming climate can greatly reduce the efficiency of nitrification inhibitors, which will further amplify the greenhouse gas impacts. The modified DNDC model of nitrification inhibitor modules can reliably simulate the inhibitory effect of NIs on N₂O emissions and evaluate the efficiency of NIs. This enables end-users to optimize the amount of NIs used according to the time and climate conditions of fertilizer application for increasing crop yield and reducing N₂O emissions and provides a useful tool for estimating the efficiency of NIs in agricultural management.

Fabrication and release behavior of nitrapyrin Microcapsules: Using modified melamine-formaldehyde resin as shell material

As a commonly used nitrification inhibitor, nitrapyrin can significantly improve the utilization of nitrogen in soils. However, the effectiveness of the traditional dosage form of nitrapyrin is reduced by soil adsorption. In this study, nitrapyrin was encapsulated into a melamine-formaldehyde resin microcapsule with good dispersion and release behavior using an in situ polymerization method. The nitrapyrin microcapsules were characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, and particle-size analysis. The results indicated that the microcapsules had a spherical-shell structure, a uniform morphology with nanoscale micropores on the surface, and a decent nitrapyrin loading content (67.19%). Tests revealed that the release behavior of the nitrapyrin microcapsules was outstanding and conformed to the double-release kinetic model. These results of this study indicate that the nitrapyrin microcapsules can be applied as nitrification inhibitors with beneficial environmental effects and high efficacy.

Enhanced efficiency fertilisers reduce nitrous oxide emissions and improve fertiliser 15N recovery in a Southern Australian pasture

The effects of reducing nitrogen (N) rates or using enhanced efficiency fertilisers (EEFs) (i.e. urease and nitrification inhibitors, and controlled release fertilisers) on nitrous oxide (N₂O) emissions and nitrogen use efficiency (NUE) are not well understood in temperate, rainfed pastures. A field experiment on rainfed ryegrass pasture in southern Australia examined the effect of granular urea N rate (0, 250 and 420 kg N ha^-1 over 6 months) and EEF use (at 250 kg N ha^-1 with NBPT, DMPP, or polymer coating (PCU)) on N₂O emissions, NUE and fertiliser N recovery (using ¹⁵N techniques). Cumulative net-N₂O emissions increased with N rate from 308 g N₂O-N ha^-1 (250 kg N ha^-1) to 514 g N₂O-N ha^-1 (420 kg N ha^-1). Using EEFs reduced N₂O emissions by 22% (NBPT), 44% (DMPP) and 56% (PCU) compared to urea. The emission factor (EF) (kg net N₂O-N per kg N applied) was 0.12 for both N rates (250 and 420 kg N ha^-1) but reduced with the EEFs to 0.10 (NBPT) and 0.07 (DMPP and PCU) compared to urea. EEF use had no significant impact on biomass or apparent NUE but led to a greater recovery of N in the soil after one month (44.8% (DMPP) and 45.9% (NBPT) compared to urea (33.7%)). Within one month 42% of the N applied as urea (U50) was lost from the plant-soil system, which was reduced with DMPP (32% loss) and NBPT (33% loss). After six months, 52% (U50) to 59% (U84) of the urea N applied was lost. The positive effect of the EEFs on N₂O emissions, and the increased recovery of N in the soil-plant system with the EEFs over one month indicates they could provide longer term benefits though soil N storage, and could be applied at lower N rates to achieve NUE benefit.

Combined effects of nitrification inhibitor and zeolite on greenhouse gas fluxes and corn growth

Field and incubation experiments were conducted to determine the emission rate of greenhouse gases, nitrogen change, populations of AOB, NOB, and fungi as well as growth of corn in response to amendment of urea granulated with and without nitrification inhibitors and zeolite. The application of urea with neem, urea with zeolite, urea with zeolite + neem, urea with zeolite + dicyandiamide, and urea with dicyandiamide (UD) decreased the N₂O emissions by 16.3%, 59.6%, 66.8%, 81.9%, 16.3%, and 86.7%, respectively. Meanwhile, patterns of CH₄ fluxes were mostly determined by small emissions. Increase in corn height, weight of cobs, biomass, and chlorophyll leaf contents were not significantly different between urea alone and urea with NIs and zeolite. In the incubation experiment, the highest concentration of NH₄⁺ and N₂O production was detected during the first week and it remained high up to the second week of incubation in the combination of urea with NIs and zeolite treatments, although there was no significant difference compared with urea. During NH₄⁺ decrease, the concentration of NO₃^- started to accumulate from the second to the third weeks. Production of CO₂ showed no significant differences among treatments. The static production of CO₂ could also explain that NIs and zeolite additions did not change AOB, NOB, and fungi activities after the fourth week of incubation.

Multiple-stressor effects of dicyandiamide (DCD) and agricultural stressors on trait-based responses of stream benthic algal communities

Agricultural practices often result in multiple stressors affecting stream ecosystems, and interacting stressors complicate environmental assessment and management of impacted streams. The nitrification inhibitor dicyandiamide (DCD) is used for nitrogen management on farmland. Effects of leached DCD on stream ecosystems are still largely unstudied, even though it could be relevant as a stressor on its own or in combination with other agricultural stressors. We conducted two experiments in 128 outdoor stream-fed mesocosms to assess stressor effects on biomass, cell density, taxon richness, evenness and functional trait composition of benthic algal communities. First, we examined responses to a wide DCD gradient (eight concentrations, 0-31 mg L^-1) and two additional stressors, deposited fine sediment (none, high) and nutrient enrichment (ambient, enriched). Second, we determined algal responses to four stressors: DCD, sediment, nutrients, and reduced flow velocity. Here DCD treatments included controls, constant application (1.4 mg L^-1) and two pulsed treatments mimicking concentration patterns in real streams (peaks 3.5 mg L^-1, 2.2 mg L^-1). Sediment and nutrient enrichment were influential stressors in both experiments, with fine sediment having the most pervasive effects. In Experiment 2, reduced flow velocity had pervasive effects and stressor interactions were mainly restricted to two-way interactions. DCD had few, weak stressor main effects, especially at field-realistic concentrations (Experiment 2). At the highest concentrations in Experiment 1 (above levels observed in real streams), DCD effects were still rare but some significant stressor interactions occurred. Analyses of functional traits were helpful in identifying potential mechanisms driving changes in densities and community composition. These findings suggest that, while DCD on its own may be a minor stressor, it could have adverse effects on algal communities already exposed to other stressors, a scenario common in agricultural streams.

Effects of urease and nitrification inhibitors on soil N, nitrifier abundance and activity in a sandy loam soil

Inhibitors of urease and ammonia monooxygenase can limit the rate of conversion of urea to ammonia and ammonia to nitrate, respectively, potentially improving N fertilizer use efficiency and reducing gaseous losses. Winter wheat grown on a sandy soil in the UK was treated with urea fertilizer with the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT), the nitrification inhibitor dicyandiamide (DCD) or a combination of both. The effects on soil microbial community diversity, the abundance of genes involved in nitrification and crop yields and net N recovery were compared. The only significant effect on N-cycle genes was a transient reduction in bacterial ammonia monooxygenase abundance following DCD application. However, overall crop yields and net N recovery were significantly lower in the urea treatments compared with an equivalent application of ammonium nitrate fertilizer, and significantly less for urea with DCD than the other urea treatments.

Aged biochar stimulated ammonia-oxidizing archaea and bacteria-derived N2O and NO production in an acidic vegetable soil

Both nitrous oxide (N₂O) and nitric oxide (NO) emissions are typically high in greenhouse-based high N input vegetable soils. Biochar amendment has been widely recommended for mitigating soil N₂O emissions in agriculture. However, knowledge of the regulatory mechanisms of fresh and aged biochar for both N₂O and NO production during ammonia oxidation is lacking. Two vegetable soils with different pH values were used in aerobic incubation experiments with 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO), 1-octyne and acetylene. The relative importance of ammonia-oxidizing archaea (AOA) and bacteria (AOB) to N₂O and NO production was investigated as influenced by fresh and aged biochar amendments. The results showed that AOA dominated N₂O production in acidic soil, while AOB dominated N₂O production in alkaline soil. Aged biochar stimulated both AOA- and AOB-derived N₂O and NO production by 84.8 and 340%, respectively, in acidic soil but only increased AOA-derived N₂O and NO production in alkaline soil. Fresh biochar amendment increased AOA- and AOB-derived NO in acidic soil and AOA-derived NO in alkaline soil but had negligible effects on AOA- and AOB-derived N₂O in both soils. Fresh biochar decreased AOA-amoA but increased AOB-amoA gene abundances in acidic soil, whereas aged biochar increased AOA- and AOB-amoA gene abundances in both soils. These findings improved our understanding of N₂O and NO production mechanisms under different biochar amendments in alkaline and acidic vegetable soils.

Using urease and nitrification inhibitors to decrease ammonia and nitrous oxide emissions and improve productivity in a subtropical pasture

Urease and nitrification inhibitors are designed to mitigate ammonia (NH₃) volatilization and nitrous oxide (N₂O) emission, but uncertainties on the agronomic and economic benefits of these inhibitors prevent their widespread adoption in pasture systems, particularly in subtropical regions where no such information is available. Here we report a field experiment that was conducted in a subtropical pasture in Queensland, Australia to examine whether the use of the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT, applied as Green UreaNV®) and the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP, applied as Urea with ENTEC®) is environmentally, agronomically and economically viable. We found that Green UreaNV® and Urea with ENTEC® decreased NH₃ volatilization and N₂O emission by 44 and 15%, respectively, compared to granular urea. Pasture biomass and nitrogen (N) uptake were increased by 22-36% and 23-32%, respectively, with application of the inhibitors compared to granular urea. A simple economic assessment indicates that the fertilizer cost for pasture production was 5.4, 4.4 and 6.0 Australian cents per kg dry matter for urea, Green UreaNV® and Urea with ENTEC®, respectively, during the experimental period. The mitigation of N loss using the inhibitors can reduce the environmental cost associated with pasture production. These results suggest that the use of these inhibitors can provide environmental, agronomic and economic benefits to a subtropical pasture.

The effect of nitrification inhibitors on NH3 and N2O emissions in highly N fertilized irrigated Mediterranean cropping systems

There is an increasing concern about the negative impacts associated to the release of reactive nitrogen (N) from highly fertilized agro-ecosystems. Ammonia (NH₃) and nitrous oxide (N₂O) are harmful N pollutants that may contribute both directly and indirectly to global warming. Surface applied manure, urea and ammonium (NH₄⁺) based fertilizers are important anthropogenic sources of these emissions. Nitrification inhibitors (NIs) have been proposed as a useful technological approach to reduce N₂O emission although they can lead to large NH₃ losses due to increasing NH₄⁺ pool in soils. In this context, a field experiment was carried out in a maize field with aiming to simultaneously quantify NH₃ volatilization and N₂O emission, assessing the effect of two NIs 3,4‑dimethilpyrazol phosphate (DMPP) and 3,4‑dimethylpyrazole succinic acid (DMPSA). The first treatment was pig slurry (PS) before seeding (50 kg N ha^-1) and calcium ammonium nitrate (CAN) at top-dressing (150 kg N ha^-1), and the second was DMPP diluted in PS (PS + DMPP) (50 kg N ha^-1) and CAN + DMPSA (150 kg N ha^-1) also before seeding and at top-dressing, respectively. Ammonia emissions were quantified by a micrometeorological method during 20 days after fertilization and N₂O emissions were assessed using manual static chambers during all crop period. The treatment with NIs was effective in reducing c. 30% cumulative N₂O losses. However, considering only direct N₂O emissions after second fertilization event, a significant reduction was not observed using CAN+DMPSA, probably because high WFPS of soil, driven by irrigation, favored denitrification. Cumulative NH₃ losses were not significantly affected by NIs. Indeed, NH₃ volatilization accounted 14% and 10% of N applied in PS + DMPP and PS plots, respectively and c. 2% of total N applied in CAN+DMPSA and CAN plots. Since important NH₃ losses still exist even although abating strategies are implemented, structural and political initiatives are needed to face this issue.

The contribution of cattle urine and dung to nitrous oxide emissions: Quantification of country specific emission factors and implications for national inventories

Urine patches and dung pats from grazing livestock create hotspots for production and emission of the greenhouse gas, nitrous oxide (N₂O), and represent a large proportion of total N₂O emissions in many national agricultural greenhouse gas inventories. As such, there is much interest in developing country specific N₂O emission factors (EFs) for excretal nitrogen (EF_3, pasture, range and paddock) deposited during gazing. The aims of this study were to generate separate N₂O emissions data for cattle derived urine and dung, to provide an evidence base for the generation of a country specific EF for the UK from this nitrogen source. The experiments were also designed to determine the effects of site and timing of application on emissions, and the efficacy of the nitrification inhibitor, dicyandiamide (DCD) on N₂O losses. This co-ordinated set of 15 plot-scale, year-long field experiments using static chambers was conducted at five grassland sites, typical of the soil and climatic zones of grazed grassland in the UK. We show that the average urine and dung N₂O EFs were 0.69% and 0.19%, respectively, resulting in a combined excretal N₂O EF (EF₃), of 0.49%, which is <25% of the IPCC default EF₃ for excretal returns from grazing cattle. Regression analysis suggests that urine N₂O EFs were controlled more by composition than was the case for dung, whilst dung N₂O EFs were more related to soil and environmental factors. The urine N₂O EF was significantly greater from the site in SW England, and significantly greater from the early grazing season urine application than later applications. Dycandiamide reduced the N₂O EF from urine patches by an average of 46%. The significantly lower excretal EF₃ than the IPCC default has implications for the UK's national inventory and for subsequent carbon footprinting of UK ruminant livestock products.

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

Biochar (BC) application to soils is of growing interest as a strategy to improve soil fertility and mitigate climate change. However, BC-induced alterations in the soil N cycle are currently under debate. BC has recently been shown to accelerate the emissions of N₂O via the biotic ammonium oxidation pathway, which results in lower nitrogen use efficiency and environmentally harmful losses of NO₃ and/ or N₂O. To avoid these potential losses, the use of nitrification inhibitor (NI) could provide a useful mitigation strategy for BC-amended agricultural fields. Here, we tested the sorption behavior of a model NI, the synthetic 3,4-dimethylpyrazole phosphate (DMPP) on 15-month-aged soil-BC mixtures. We saw that BC additions increased DMPP sorption to varying extents depending on BC feedstock type and pyrolysis temperature. The highest sorption was found for BC pyrolyzed at a lower temperature. BC effects on soil physico-chemical characteristics (i.e., hydrophobicity) seem to be important factors.

Multiple-year nitrous oxide emissions from a greenhouse vegetable field in China: Effects of nitrogen management

The greenhouse vegetable (GV) field is an important agricultural system in China. It may also be a hot spot of nitrous oxide (N₂O) emissions. However, knowledge on N₂O emission from GV fields and its mitigation are limited due to considerable variations of N₂O emissions. In this study, we performed a multi-year experiment at a GV field in Beijing, China, using the static opaque chamber method, to quantify N₂O emissions from GV fields and evaluated N₂O mitigation efficiency of alternative nitrogen (N) managements. The experiment period spanned three rotation periods and included seven vegetable growing seasons. We measured N₂O emissions under four treatments, including no N fertilizer use (CK), farmers' conventional fertilizer application (FP), reduced N fertilizer rate (R), and R combined with the nitrification inhibitor "dicyandiamide (DCD)" (R+DCD). The seasonal cumulative N₂O emissions ranged between 2.09 and 19.66, 1.13 and 11.33, 0.94 and 9.46, and 0.15 and 3.27kgNha^-1 for FP, R, R+DCD, and CK, respectively. The cumulative N₂O emissions of three rotational periods varied from 18.71 to 26.58 (FP), 9.58 to 15.96 (R), 7.11 to 13.42 (R+DCD), and 1.66 to 3.73kgNha^-1 (CK). The R and R+DCD treatments significantly (P<0.05) reduced the N₂O emissions under FP by 38.1% to 48.8% and 49.5% to 62.0%, across the three rotational periods, although their mitigation efficiencies were highly variable among different vegetable seasons. This study suggests that GV fields associated with intensive N application and frequent flooding irrigation may substantially contribute to the N₂O emissions and great N₂O mitigations can be achieved through reasonably reducing the N-fertilizer rate and/or applying a nitrification inhibitor. The large variations in the N₂O emission and mitigation across different vegetable growing seasons and rotational periods stress the necessity of multi-year observations for reliably quantifying and mitigating N₂O emissions for GV systems.

Feeding dicyandiamide (DCD) to cattle: An effective method to reduce N2O emissions from urine patches in a heavy-textured soil under temperate climatic conditions

Nitrate (NO₃^-) leaching and nitrous oxide (N₂O) emission from urine patches in grazed pastures are key sources of water and air pollution, respectively. Broadcast spraying of the nitrification inhibitor dicyandiamide (DCD) has been shown to reduce these losses, but it is expensive. As an alternative, it had been demonstrated that feeding DCD to cattle (after manual mixing with supplementary feeds) was a practical, effective and cheaper method to deliver high DCD rates within urine patches. This two-year study carried out on simulated urine patches in three application seasons (spring, summer, autumn) explored the efficacy of DCD feeding to cattle to reduce N losses from grazed pasture soil in a heavy-textured soil under temperate climatic conditions. In each application season, DCD fed to cows, then excreted with urine and applied at a rate of 30kgDCDha^-1 (treatment U+DCD³⁰-f) was as effective as powdered DCD mixed with normal urine and applied at the same rate (treatment U+DCD³⁰) at reducing cumulative N₂O-N emissions and the N₂O-N emission factor (EF3, expressed as % of N applied). Increasing DCD loading within urine patches from 10 to 30kgDCDha^-1 improved efficacy by significantly reducing the EF3 from 34% to 64%, which highlights that under local conditions, 10kgDCDha^-1 (the recommended rate for commercial use in New Zealand) was not the optimum DCD rate to curb N₂O emissions. The modelling of EF3 in this study also suggests that N mitigation should be given more attention when soil moisture is going to be high, which can be predicted with short-term weather forecasting. DCD feeding, for instance in autumn when cows are not lactating and the risk of N losses is high, could then be reduced by focusing mainly on those forecasted wet periods.

Nitrification inhibitors mitigated reactive gaseous nitrogen intensity in intensive vegetable soils from China

Nitrification inhibitors, a promising tool for reducing nitrous oxide (N₂O) losses and promoting nitrogen use efficiency by slowing nitrification, have gained extensive attention worldwide. However, there have been few attempts to explore the broad responses of multiple reactive gaseous nitrogen emissions of N₂O, nitric oxide (NO) and ammonia (NH₃) and vegetable yield to nitrification inhibitor applications across intensive vegetable soils in China. A greenhouse pot experiment with five consecutive vegetable crops was performed to assess the efficacies of two nitrification inhibitors, namely, nitrapyrin and dicyandiamide on reactive gaseous nitrogen emissions, vegetable yield and reactive gaseous nitrogen intensity in four typical vegetable soils representing the intensive vegetable cropping systems across mainland China: an Acrisol from Hunan Province, an Anthrosol from Shanxi Province, a Cambisol from Shandong Province and a Phaeozem from Heilongjiang Province. The results showed soil type had significant influences on reactive gaseous nitrogen intensity, with reactive gaseous nitrogen emissions and yield mainly driven by soil factors: pH, nitrate, C:N ratio, cation exchange capacity and microbial biomass carbon. The highest reactive gaseous nitrogen emissions and reactive gaseous nitrogen intensity were in Acrisol while the highest vegetable yield occurred in Phaeozem. Nitrification inhibitor applications decreased N₂O and NO emissions by 1.8-61.0% and 0.8-79.5%, respectively, but promoted NH₃ volatilization by 3.2-44.6% across all soils. Furthermore, significant positive correlations were observed between inhibited N₂O+NO and stimulated NH₃ emissions with nitrification inhibitor additions across all soils, indicating that reduced nitrification posed the threat of NH₃ losses. Additionally, reactive gaseous nitrogen intensity was significantly reduced in the Anthrosol and Cambisol due to the reduced reactive gaseous nitrogen emissions and increased yield, respectively. Our findings highlight the benefits of nitrification inhibitors for integrating environment and agronomy in intensive vegetable ecosystems in China.

Assessment of N2O emissions from a fertilised vegetable cropping soil under different plant residue management strategies using 15N tracing techniques

Combined application of plant residues and N fertilisers strongly affect soil mineral N dynamics and N₂O emissions depending on the quality of the plant residues, their application methods and other management strategies. We investigated the effect of combined application of two vegetable plant residues (cauliflower and sweet corn) and ¹⁵N fertiliser on N dynamics and N₂O emission in a glasshouse pot study. The experiment was conducted under two residue management practices (soil incorporation vs surface mulching) over 98days with growing basil (Ocimum basilicum) plants. We also assessed the efficacy of applying the nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP) to the plant residues, for reducing N loss and mitigating N₂O emissions. Application of plant residues, both on the soil surface or into soil, resulted in net N mineralisation and increased cumulative N₂O emission compared with the application of N fertiliser alone. Soil surface mulching of sweet corn decreased total and residue-induced cumulative N₂O emission compared with the incorporation method, while it showed opposite effect on N₂O emissions from cauliflower residue. The application of DMPP with sweet corn residue reduced total, residue- and fertiliser-induced N₂O emissions; however its application with cauliflower residue did not show any mitigating effect on the N₂O emissions. The residue application methods and the use of DMPP did not significantly affect ¹⁵N recovery by the basil plants. In contrast, soil incorporation of these residues doubled the microbial immobilisation of applied ¹⁵N into soil organic matter. Linear regression analysis of N₂O emission during the experimental period indicated that in the treatments without DMPP application, soil NO₃^--N concentration was the most important factor in controlling the magnitude of N₂O emissions, while the application of DMPP changed the dominant regulating factor from NO₃^--N to NH₄⁺-N concentration.

Determination of 3,5 - dimethylpyrazolium glyceroborate nitrification inhibitor in nitrogen fertilizer samples: HPLC-DAD method development and validation for 3,5 - dimethylpyrazole

3,5 - Dimethylpyrazolium glyceroborate is a nitrification inhibitor (a member of pyrazole derivatives) used for the fixation of nitrogen into the soil. In this study, an HPLC-DAD method was developed and validated for determination of 3,5 - dimethylpyrazole in order to determine 3,5 - dimethylpyrazolium glyceroborate in fertilizer samples. For method development, analytical parameters like type of eluent solution and column filling material and device parameters like eluent flow rate, column oven temperature and measurement wavelength were all optimized. For method validation, implementations were performed for linearity, limit of detection (LOD), limit of quantification (LOQ), specificity, stability, intra- and inter-day precision and accuracy. The developed and validated method was used for inhibitor detection in nitrogenous fertilizers. Sample analyses were performed with 95.6-103.3% recovery rates and 0-4.61% relative errors.

Effects of dicyandiamide and acetylene on N2O emissions and ammonia oxidizers in a fluvo-aquic soil applied with urea

Ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) are crucial for N₂O emission as they carry out the key step of nitrification. Dicyandiamide (DCD) and acetylene (C₂H₂) are typical nitrification inhibitors (NIs), while the comparative effects of these NIs on N₂O production and ammonia oxidizers' (AOB and AOA) growth are unclear. Four treatments including a control, urea, urea + DCD, and urea + C₂H₂ were set up to investigate their effect of inhibiting soil nitrification, nitrification-related N₂O emission as well as the growth of ammonia oxidizers with a fluvo-aquic soil using microcosms for 28 days. N₂O emission and net nitrification rate increased after the application of urea, but were significantly restrained in urea + NI treatments, while C₂H₂ was more effective in reducing N₂O emission and nitrification rate than DCD. The abundance of AOB, which was significantly correlated with N₂O emission and net nitrification rate, was more inhibited by C₂H₂ than DCD. Furthermore, the application of urea in all the soils had little impact on the AOA community, while obvious shifts of AOB community structure were found compared with the control. All AOB sequences fell within Nitrosospira cluster 3, and the AOA community was clustered to group 1.1b. Collectively, it indicated that application of urea combined with NIs (DCD or C₂H₂) could potentially alter N₂O emission, mainly through regulating the growth of AOB but not AOA in this fluvo-aquic soil.

Application effects of coated urea and urease and nitrification inhibitors on ammonia and greenhouse gas emissions from a subtropical cotton field of the Mississippi delta region

Nitrogen (N) fertilization affects both ammonia (NH3) and greenhouse gas (GHG) emissions that have implications in air quality and global warming potential. Different cropping systems practice varying N fertilizations. The aim of this study was to investigate the effects of applications of polymer-coated urea and urea treated with N process inhibitors: NBPT [N-(n-butyl)thiophosphoric triamide], urease inhibitor, and DCD [Dicyandiamide], nitrification inhibitor, on NH3 and GHG emissions from a cotton production system in the Mississippi delta region. A two-year field experiment consisting of five treatments including the Check (unfertilized), urea, polymer-coated urea (ESN), urea+NBPT, and urea+DCD was conducted over 2013 and 2014 in a Cancienne loam (Fine-silty, mixed, superactive, nonacid, hyperthermic Fluvaquentic Epiaquepts). Ammonia and GHG samples were collected using active and passive chamber methods, respectively, and characterized. The results showed that the N loss to the atmosphere following urea-N application was dominated by a significantly higher emission of N2O-N than NH3-N and the most N2O-N and NH3-N emissions were during the first 30-50 days. Among different N treatments compared to regular urea, NBPT was the most effective in reducing NH3-N volatilization (by 58-63%), whereas DCD the most significant in mitigating N2O-N emissions (by 75%). Polymer-coated urea (ESN) and NBPT also significantly reduced N2O-N losses (both by 52%) over urea. The emission factors (EFs) for urea, ESN, urea-NBPT, urea+DCD were 1.9%, 1.0%, 0.2%, 0.8% for NH3-N, and 8.3%, 3.4%, 3.9%, 1.0% for N2O-N, respectively. There were no significant effects of different N treatments on CO2-C and CH4-C fluxes. Overall both of these N stabilizers and polymer-coated urea could be used as a mitigation strategy for reducing N2O emission while urease inhibitor NBPT for reducing NH3 emission in the subtropical cotton production system of the Mississippi delta region.

Slow delivery of a nitrification inhibitor (dicyandiamide) to soil using a biodegradable hydrogel of chitosan

Using chemical inhibitors to reduce soil nitrification decreases emissions of environmental damaging nitrate and nitrous oxide and improves nitrogen use efficiency in agricultural systems. The efficacy of nitrification inhibitors such as dicyandiamide (DCD) is limited in soil due to biodegradation. This study investigated if the persistence of DCD could be sustained in soil by slow release from a chitosan hydrogel. DCD was encapsulated in glyoxal-crosslinked chitosan beads where excess glyoxal was (i) partly removed (C beads) or (ii) allowed to dry (CG beads). The beads were tested in water and in soil. The beads contained two fractions of DCD: one which was quickly released in water, and one which was not. A large DCD fraction within C beads was readily available: 84% of total DCD bead content was released after 9h immersion in water, while between 74% and 98% was released after 7d in soil under low to high moisture conditions. A lower percentage of encapsulated DCD was readily released from CG beads: 19% after 9h in water, and 33% after 7d in soil under high rainfall conditions. Kinetic analysis indicated that the release in water occurred by quasi-Fickian diffusion. The results also suggest that DCD release was controlled by bead erosion and the leaching of glyoxal derivatives, predominantly a glyoxal-DCD adduct whose release was positively correlated with that of DCD (R(2)=0.99, p⩽0.0001). Therefore, novel chitosan/glyoxal composite beads show a promising slow-release potential in soil for agrochemicals like DCD.