Nitrification Inhibitor Dicyandiamide Research Articles

Injection and Nitrification Inhibitor Improve the Recovery of Pig Slurry Ammonium Nitrogen in Grain Crops in Brazil

Efficient management practices are needed for no‐till (NT) cropping systems fertilized with pig slurry (PS). We evaluated the effect of application mode (surface broadcasting vs. injection) with or without the nitrification inhibitor dicyandiamide (DCD), on the recovery of PS ammonium nitrogen (NH4–N) in 2‐yr crop succession (corn [Zea mays L.]/oat [Avena strigosa L.]/corn/wheat [Triticum aestivum L.]) under NT and irrigation. Each crop received PS at planting. The NH4‐N fraction of PS was enriched with 15N to discriminate the contribution of current vs. past applications to crop N uptake. Compared to surface application, injection increased corn uptake of PS NH4–N by 22 kg N ha−1 under low precipitation regime, likely because it efficiently reduced ammonia volatilization; the effect was small under high precipitation regime and in winter crops in general. To the contrary, DCD doubled the uptake of PS NH4–N in corn (+24 kg N ha−1) under high precipitation regime, likely because it reduced losses through N leaching, whereas the gain was smaller under drier conditions and in winter crops in general. Because of this complementary response to injection and DCD, the retention of PS NH4–N in the soil–plant system for the whole crop succession was maximized where PS was injected in combination with DCD, being 19 to 23% greater than injection or DCD alone. The injection of DCD‐treated PS is therefore recommended to maximize crop uptake of PS NH4–N and minimize environmental losses under irrigated NT conditions in southern Brazil.Core Ideas Injection of dicyandiamide‐treated pig slurry is a recommendable practice to maximize crop uptake of pig slurry NH4–N. Injection of dicyandiamide‐treated pig slurry is a recommendable practice to minimize environmental N losses. Injection was more efficient under dryer than wetter conditions. Dicyandiamide added to pig slurry improved the retention of pig slurry NH4–N only under wet conditions.

Effectiveness of the nitrification inhibitor dicyandiamide and biochar to reduce nitrous oxide emissions

ABSTRACTAnimal urine from grazing animals is responsible for the majority of New Zealand’s nitrous oxide (N2O) emissions. A field lysimeter study was conducted to determine the ability of the combination of the nitrification inhibitor dicyandiamide (DCD) and biochar to mitigate N2O emissions from a winter grazing forage crop soil. The results showed that over a 4 month period, applying cow urine at a rate of 700 kg N ha−1 increased N2O emissions from 0.7 kg N2O-N ha−1 to 14.7 kg N2O-N ha−1. The application of DCD at 20 kg ha−1 reduced total N2O emissions by 65%. The application of biochar at 5 t ha−1 had no significant effect on N2O emissions. The combination of DCD with biochar did not lead to greater N2O reductions than DCD alone. These results indicated that DCD was highly effective whereas biochar was ineffective in reducing N2O emissions in the winter forage soil.

Variation in characteristics of air concentrations of NH3, NO2 and O3 induced by applications of urea in soils of plastic greenhouses in suburban China

Few studies have been carried out so far for measuring concentrations of NH3, NO2 and O3 in plastic greenhouses. In this study, NH3, NO2 and O3 concentrations were measured with passive sampler technology in a plastic greenhouse located in the Changsha suburb in southern China over a one and a half month period (November 30, 2008 to January 11, 2009). Soil in the greenhouse was subjected to four treatment (T) types (no N fertilizer T1, common urea T2, coated urea T3 and common urea with nitrification inhibitor dicyandiamide (DCD) T4. The average concentrations (μg/m3) of NH3, NO2 and O3 in descending order was: T4 (31.66) > T2 (25.93) > T3 (23.52) > T1 (7.96), T2 (10.99) > T3 (8.16) > T4 (7.48) > T1 (5.20), T2 (75.05) > T3 (64.20) > T4 (63.85) > T1 (49.02), respectively. This implied that photochemical reactions took place and that harmful gases accumulated after application of N fertilizer in the plastic greenhouse. DCD inhibited the conversion of ammonium to nitrate, increased NH3 volatilization and decreased NO2 level. The coated urea decreased the emissions of NH3 and increased nitrogen use efficiency. We found significant positive correlations (p < 0.01) between temperature and both NH3 and NO2 levels. Correlations between soil pH and both NH3 and NO2 concentrations were also significant (p < 0.01). The O3 average concentration from March 31, 2009 to April 10, 2009 in the higher latitude of the Yinchuan suburb in northern China was two times greater than that in the Changsha suburb in southern China. The O3 daily concentrations in the Yinchuan suburb exceeded 160 μg/m3 (i.e., China's Grade I standard), and the maximal value 214.83 μg/m3 exceeded 200 μg/m3 (i.e., China's Grade III standard).

NO and N2O emissions from agricultural fields in the North China Plain: Origination and mitigation

Agricultural soil has been recognized as a major source of atmospheric NO and N2O emissions which have important impacts on regional and global environments. Here we comparably investigated the effects of ammonium, nitrate fertilizers and nitrification inhibitor dicyandiamide (DCD) addition on NO and N2O emissions from the agricultural soil in the North China Plain (NCP). Compared with the ammonium fertilizer application, the reductions of NO emissions caused by nitrate fertilizer and DCD addition were 100% and 93%, and of N2O emissions were 54% and 74%, respectively. Remarkable reductions of NO and N2O emissions were also observed from five different agricultural soils in the NCP by replacing ammonium with nitrate fertilizer, indicating that nitrification is the predominant process for the emissions of NO and N2O from the soils in the vast area of NCP. NO emission peaks were found to be several days later than N2O peaks after the application of ammonium fertilizer and flooding irrigation, implying that most of NO initially produced via nitrification process might be fast reduced to N2O under the high soil moisture condition. Interestingly, the relative contribution of denitrification to N2O emission showed obviously time-dependent, e.g., evident N2O emission caused by the application of nitrate was only observed after the basal fertilization for the maize and the topdressing for the wheat. Replacing ammonium with nitrate fertilizer and mixing with the nitrification inhibitor are verified to be effective measures for mitigating NO and N2O emissions from arable soils in the NCP.

Short‐term effects of polyacrylamide and dicyandiamide on C and N mineralization in a sandy loam soil

AbstractThe soil conditioners anionic polyacrylamide (PAM) and dicyandiamide (DCD) are frequently applied to soils to reduce soil erosion and nitrogen loss, respectively. A 27‐day incubation study was set up to gauge their interactive effects on the microbial biomass, carbon (C) mineralization and nitrification activity of a sandy loam soil in the presence or absence of maize straw. PAM‐amended soils received 308 or 615 mg PAM/kg. Nitrogen (N)‐fertilized soils were amended with 1800 mg/kg ammonium sulphate [(NH4)2SO4], with or without 70 mg DCD/kg. Maize straw was added to soil at the rate of 4500 mg/kg. Maize straw application increased soil microbial biomass and respiration. PAM stimulated nitrification and C mineralization, as evidenced by significant increases in extractable nitrate and evolved carbon dioxide (CO2) concentrations. This is likely to have been effected by the PAM improving microbial conditions and partially being utilized as a substrate, with the latter being indicated by a PAM‐induced significant increase in the metabolic quotient. PAM did not reduce the microbial biomass except in one treatment at the highest application rate. Ammonium sulphate stimulated nitrification and reduced microbial biomass; the resultant acidification of the former is likely to have caused these effects. N fertilizer application may also have induced short‐term C‐limitation in the soil with impacts on microbial growth and respiration. The nitrification inhibitor DCD reduced the negative impacts on microbial biomass of (NH4)2SO4 and proved to be an effective soil amendment to reduce nitrification under conditions where mineralization was increased by addition of PAM.

Quantifying N2O emissions from intensive grassland production: the role of synthetic fertilizer type, application rate, timing and nitrification inhibitors

SUMMARYIncreasing recognition of the extent to which nitrous oxide (N2O) contributes to climate change has resulted in greater demand to improve quantification of N2O emissions, identify emission sources and suggest mitigation options. Agriculture is by far the largest source and grasslands, occupyingc. 0·22 of European agricultural land, are a major land-use within this sector. The application of mineral fertilizers to optimize pasture yields is a major source of N2O and with increasing pressure to increase agricultural productivity, options to quantify and reduce emissions whilst maintaining sufficient grassland for a given intensity of production are required. Identification of the source and extent of emissions will help to improve reporting in national inventories, with the most common approach using the IPCC emission factor (EF) default, where 0·01 of added nitrogen fertilizer is assumed to be emitted directly as N2O. The current experiment aimed to establish the suitability of applying this EF to fertilized Scottish grasslands and to identify variation in the EF depending on the application rate of ammonium nitrate (AN). Mitigation options to reduce N2O emissions were also investigated, including the use of urea fertilizer in place of AN, addition of a nitrification inhibitor dicyandiamide (DCD) and application of AN in smaller, more frequent doses. Nitrous oxide emissions were measured from a cut grassland in south-west Scotland from March 2011 to March 2012. Grass yield was also measured to establish the impact of mitigation options on grass production, along with soil and environmental variables to improve understanding of the controls on N2O emissions. A monotonic increase in annual cumulative N2O emissions was observed with increasing AN application rate. Emission factors ranging from 1·06–1·34% were measured for AN application rates between 80 and 320 kg N/ha, with a mean of 1·19%. A lack of any significant difference between these EFs indicates that use of a uniform EF is suitable over these application rates. The mean EF of 1·19% exceeds the IPCC default 1%, suggesting that use of the default value may underestimate emissions of AN-fertilizer-induced N2O loss from Scottish grasslands. The increase in emissions beyond an application rate of 320 kg N/ha produced an EF of 1·74%, significantly different to that from lower application rates and much greater than the 1% default. An EF of 0·89% for urea fertilizer and 0·59% for urea with DCD suggests that N2O quantification using the IPCC default EF will overestimate emissions for grasslands where these fertilizers are applied. Large rainfall shortly after fertilizer application appears to be the main trigger for N2O emissions, thus applicability of the 1% EF could vary and depend on the weather conditions at the time of fertilizer application.

Nitrous oxide emissions from urea fertiliser and effluent with and without inhibitors applied to pasture

There is currently a limited number of New Zealand studies quantifying nitrous oxide (N2O) emission factors (EF1, N2O emissions as a percentage of N applied) for farm dairy effluent (FDE) and urea fertiliser. Therefore, two experiments were conducted in four regions of New Zealand to determine EF1 for FDE and urea fertiliser applied to pastures with contrasting soils and climatic conditions. Experiment 1 included urease and nitrification inhibitors to determine their effect on EF1. Urea treatments included (i) standard urea; (ii) urea amended with the nitrification inhibitor dicyandiamide (DCD) at 0.02kgDCDkg−1 nitrogen (N) and (iii) urea amended with the urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT) at 250mgnBTPTkg−1urea, while FDE was applied with or without DCD, at 10kgDCDha−1. Experiment 2 focused solely on FDE, which was applied to pastures that had either never received FDE or had a history of repeated application of FDE over several years. Urea fertiliser produced a large variation in EF1 values, ranging from 0.03% to 1.52%. Application of FDE resulted in EF1 ranging from 0.06% to 0.94% across both experiments. The urease and nitrification inhibitors had little or no effect on reducing EF1 from urea fertiliser and FDE application. The history of repeated applications of FDE to pasture also had no effect on EF1.

Evidence that the efficacy of the nitrification inhibitor dicyandiamide (DCD) is affected by soil properties in UK soils

A laboratory incubation study was conducted with nine UK soils to determine the effect of soil physical and chemical properties, and temperature, on the efficacy the nitrification inhibitor dicyandiamide (DCD). Nitrogen was applied to soil as ammonium chloride at a rate of 100 μg N g−1 dry soil, and incubated at 60% water-filled-pore-space at either 5, 15 or 25 °C. The ammonium (NH4+) pool was enriched with 15N to 60 atom% excess and DCD was applied at a rate of 10 μg g−1 dry soil. The concentrations and enrichments of the NH4+ and nitrate (NO3−) pools, along with nitrous oxide (N2O) flux measurements, were determined regularly for 60 days after N application. Gross soil N transformation rates were quantified with a 15N tracing model. The persistence of DCD was strongly related (P < 0.001) to temperature with the measured half-life across all soils of 89, 37 and 18 days at 5, 15, and 25 °C, respectively. There was wide variation in the half-life of DCD among soils; which was predominantly associated with the soil oxalate extractable Fe concentration. Greater (P < 0.001) inhibition in autotrophic nitrification by DCD occurred at 5 and 15 °C compared to 25 °C. Across all soils and temperatures DCD increased the rate of mineralisation of recalcitrant organic-N and the rate of adsorption of free NH4+, however, effects varied between soils. DCD did not have a significant effect on the rate of oxidation of recalcitrant organic-N to NO3− or on any of the immobilisation processes or mineralisation of labile N to NH4+. The efficacy of DCD in inhibiting net NO3− production best correlated with soil Cu (r = −0.82), % clay (r = −0.71), total N (r = −0.66) and LOI (r = −0.61). Stepwise multiple regression showed that Cu, oxalate extractable Fe and oxalate extractable Al explained 85.0% of the variation in the percentage inhibition of net NO3− production by DCD. The inhibitor also reduced cumulative N2O emissions, with reductions negatively correlated with a range of soil properties associated with organic matter. We provide evidence that the interaction between temperature, soil clay content and soil organic matter governs the efficacy of DCD. The grassland soils had higher native total N concentrations than the arable soils, hence the inhibition of net NO3− production by DCD was lower and this resulted in an overall inhibition in N2O emissions of 58% and 81% for grassland and arable soils respectively.

Amendment of cattle slurry with the nitrification inhibitor dicyandiamide during storage: A new effective and practical N2O mitigation measure for landspreading

Large quantities of organic manures and soiled water are generated by cattle housing every year. These organic wastes are stored until soil conditions are suitable for landspreading or there is a crop requirement for nutrients. After land application, some nitrogen (N) is lost through the direct emission of nitrous oxide (N2O), a powerful greenhouse gas (GHG) produced by nitrification and partial denitrification of mineral N. The objective of this research was to investigate whether N2O losses could be mitigated after applying cattle slurry pre-mixed with the nitrification inhibitor dicyandiamide (DCD) during anaerobic storage. Contrary to our initial hypothesis, DCD mixed with slurry did not degrade for up to six months post amendment during an incubation study. These results highlight the feasibility of amending cattle slurry with DCD directly into slurry tanks any time before land application. This incubation experiment also showed that a slow release of DCD in slurry could be achieved if the amendment used was beads of a chitosan xerogel impregnated with DCD. A field study revealed that slurry application to grassland plots can cause large N2O emissions under wet and mild conditions when ammonia emissions are expected to be low. Slurry incubated with DCD for six month was effective at significantly (P<0.01) decreasing N2O net cumulative emissions, which were 88% lower than in the slurry treatment with no DCD. The addition of DCD to slurry also reduced the fraction of N2O in the total GHG net cumulative emissions from 52% down to just 10%. Mixing slurry with DCD during storage could therefore offer farmers a cost-effective, practical, mitigation alternative to DCD broadcast application for the reduction of agricultural N losses.

Ammonia emissions from cattle dung, urine and urine with dicyandiamide in a temperate grassland

AbstractDeposition of urine and dung in pasture‐based livestock production systems is a major source of ammonia (NH3) volatilization, contributing to the eutrophication and acidification of water bodies and to indirect nitrous oxide emissions. The objectives of this study were to (i) measure NH3 volatilization from dung and urine in three seasons, (ii) test the effect of spiking urine with the nitrification inhibitor dicyandiamide (DCD) on NH3 volatilization and (iii) generate NH3 emission factors (EFs) for dung, urine and urine + DCD in temperate maritime grassland. Accordingly, simulated dung, urine and urine spiked with DCD (at 30 kg DCD/ha equivalent rate) patches were applied to temperate grassland. Treatments were applied three times in 2014 with one measurement of NH3 loss being completed in spring, summer and autumn. The NH3‐N EF was highest in spring, which was most likely due to the near absence of rainfall throughout the duration of loss measurement. The EFs across the experiments ranged between 2.8 and 5.3% (mean 3.9%) for dung, 8.7 and 14.9% (mean 11.2%) for urine and 9.5 and 19.5% (mean 12.9%) for urine + DCD, showing that ammonia loss from dung was significantly lower than from urine. Aggregating country‐specific emission data such as those from the current experiment with data from climatically similar regions (perhaps in a weighted manner which accounts for the relative abundance of certain environmental conditions) along with modelling is a potentially resource‐efficient approach for refining national ammonia inventories.

Nitrous oxide emissions from fertilised UK arable soils: Fluxes, emission factors and mitigation

Cultivated agricultural soils are the largest anthropogenic source of nitrous oxide (N2O), a greenhouse gas approx. 298 times stronger than carbon dioxide. As agricultural land covers 40–50% of the earth’s surface agricultural N2O emissions could significantly influence future climate. The timing, amount and form of manufactured nitrogen (N) fertiliser applied to soils are major controls on N2O emission magnitude, and various methods are being investigated to quantify and reduce these emissions. A lack of measured N2O emission factors (EFs) means that most countries report N2O emissions using the IPCC’s Tier 1 methodology, where an EF of 1% is applied to mineral soils, regardless of soil type, climate, or location. The aim of this research was to generate evidence from experiments to contribute to improving the UK’s N2O agricultural inventory, by determining whether N2O EFs should vary across soil types and agroclimatic zones. Mitigation methods were also investigated, including assessing the impact of the nitrification inhibitor (NI) dicyandiamide (DCD), the application of more frequent smaller doses of fertiliser, and the impact of different rates and forms of manufactured N fertiliser. Nitrous oxide emissions were measured at one cropland site in Scotland and two in England for 12 months in 2011/2012, along with soil and environmental variables. Crop yield was also measured, and emission intensities were calculated for the contrasting fertiliser treatments. The greatest mean annual cumulative emissions from a range of ammonium nitrate (AN) fertiliser rates were measured at the Scottish site (2301g N2O-N ha−1), which experienced 822mm rainfall compared to 418mm and 472mm at the English sites, where cumulative annual emissions were lower (929 and 1152g N2O-N ha−1, respectively). Climate and soil mineral N influenced N2O emissions, with a combination of factors required to occur simultaneously to generate the greatest fluxes. Emissions were related to fertiliser N rate; however the trend was not linear. EFs for AN treatments varied between sites, but at both English sites were much lower than the 1% value used by the IPCC, and as low as 0.20%. DCD reduced AN- and urea-generated N2O emissions and yield-scaled emissions at all sites. AN application in more frequent smaller doses reduced emissions at all sites, however, the type of fertiliser (AN or urea) had no impact. A significant difference in mean annual cumulative emissions between sites reflected differences in rainfall, and suggests that location specific or rainfall driven emission estimates could be considered.

The effect of precipitation and application rate on dicyandiamide persistence and efficiency in two Irish grassland soils

AbstractThe nitrification inhibitor dicyandiamide (DCD) has had variable success in reducing nitrate () leaching and nitrous oxide (N2O) emissions from soils receiving nitrogen (N) fertilizers. Factors such as soil type, temperature and moisture have been linked to the variable efficacy of DCD. As DCD is water soluble, it can be leached from the rooting zone where it is intended to inhibit nitrification. Intact soil columns (15 cm diameter by 35 cm long) were taken from luvic gleysol and haplic cambisol grassland sites and placed in growth chambers. DCD was applied at 15 or 30 kg DCD/ha, with high or low precipitation. Leaching of DCD, mineral N and the residual soil DCD concentrations were determined over 8 weeks high precipitation increased DCD in leachate and decreased recovery in soil. A soil × DCD rate interaction was detected for the DCD unaccounted (proxy for degraded DCD). In the cambisol, degradation of DCD was high (circa 81%) and unaffected by DCD rate. In contrast, DCD degradation in the gleysol was lower and differentially affected by rate, 67 and 46% for the 15 and 30 kg/ha treatments, respectively. Variation in DCD degradation rates between soils may be related to differences in organic matter content and associated microbiological activity. Variable degradation rates of DCD in soil, unrelated to temperature or moisture, may contribute to changing DCD efficacy. Soil properties should be considered when tailoring DCD strategies for improving nitrogen use efficiency and crop yields, through the reduction of reactive nitrogen loss.

Optimizing net greenhouse gas balance of a bioenergy cropping system in southeast China with urease and nitrification inhibitors

Efforts to advance our knowledge on the potential of bioenergy instead of fossil fuels in terms of mitigating climatic impact are in urgent need. No data is currently available on the use of urease and nitrification inhibitors in costal saline bioenergy cropping systems. An overall accounting of net greenhouse gas balance (NGHGB) and greenhouse gas intensity (GHGI) affected by combined effects of urease inhibitor hydroquinone (HQ) and nitrification inhibitor dicyandiamide (DCD) amendment was examined in a coastal saline Jerusalem artichoke bioenergy cropping system. The net ecosystem exchange of CO2 (NEE) was determined by the difference between soil heterotrophic respiration (RH) and net primary production (NPP) using static chamber method. Urease and nitrification inhibitors amendment increased the NPP but exerted a suppression effect on soil RH over the Jerusalem artichoke cropping system. A trade-off relationship was observed by decreasing soil N2O but stimulating soil CH4 emissions following HQ+DCD amendment. The plots combined urea with HQ+DCD application increased soil CH4 by 167% while decreased N2O by 16% as compared to with urea only in the bioenergy cropping system. On average, the fertilizer N-induced emission factor of N2O was estimated to be 0.25% across the fertilized plots. Compared with urea, the plots with urea and HQ+DCD resulted in a further decrease by 37% and 15% in estimated NGHGB and GHGI over the Jerusalem artichoke cropping system, respectively. Overall, Jerusalem artichoke production would achieve higher biomass as source of biofuels but lower climatic impacts, particularly when together with urease and nitrification inhibitors amendment in coastal saline soils.

Impact of urine and the application of the nitrification inhibitor DCD on microbial communities in dairy-grazed pasture soils

Tools to manage the emission of the greenhouse gas nitrous oxide (N2O), an intermediate of both nitrification and denitrification, from soils are limited. To date, the nitrification inhibitor dicyandiamide (DCD) is one of the most effective tools available to livestock farmers for reducing N2O emissions and minimizing leaching of nitrogen in response to increased urine deposition in grazed pasture systems. Despite its effectiveness in decreasing N losses from animal urine by inhibiting N processes in soils, the effect of DCD on the population structure of denitrifiers and overall bacterial community composition is still uncertain. Here we use three New Zealand dairy-grazed pasture soils to determine the effects of DCD application on microbial community richness and composition at both functional (genes involved in the denitrification process) and phylogenetic (overall bacterial community composition based on 16S rRNA profiling) levels. Results further confirm that the effects on microbial populations are minimal and transient in nature. The impact of DCD on microbial community structure was soil dependent, and a greater effect was attributed to intrinsic soil properties like soil texture, with community response to DCD in combination with urine being comparable to that under urine alone. Addition of DCD to cattle urine also reduced N2O emission between 23 and 67%.

Plant acquisition and metabolism of the synthetic nitrification inhibitor dicyandiamide and naturally-occurring guanidine from agricultural soils

There is increasing interest and use of nitrification inhibitors (NI) in agroecosystems, yet little is known of their fate in planta. Residues of the organic, N-rich NI, dicyandiamide (DCD), have been found in milk products following commercial application to pasture. We investigated whether plant acquisition and metabolism of DCD were consistent with plant-mediated transmission from soil to agricultural food products. Uptake rates, translocation to the shoot, degradation of the label within wheat tissue and availability within two soils of DCD and the structurally similar naturally occurring N-rich molecule, guanidine, were measured using 14C labelling. Under sterile conditions, over 2 h wheat took up (34 and 14 μmol g−1 root DW h−1 at 1 mM: DCD and guanidine, respectively), translocated (7–15 and 19–22 %) and metabolised (0.4 and 0.9 % of uptake) DCD- and guanidine-14C. Both molecules were also acquired from soil by wheat despite concurrent soil sorption and microbial uptake. Both DCD and guanidine can be acquired and metabolised by graminaceous plants. Although probably not a significant route of N acquisition, plant uptake provides a direct route of DCD entry into the food chain.

Enhanced-Efficiency Fertilizers in Nitrous Oxide Emissions from Urea Applied to Sugarcane

The environmental benefits of producing biofuels from sugarcane have been questioned due to greenhouse gas emissions during the biomass production stage, especially nitrous oxide (NO) associated with nitrogen (N) fertilization. The objective of this work was to evaluate the use of nitrification inhibitors (NIs) dicyandiamide (DCD) and 3,4 dimethylpyrazole phosphate (DMPP) and a controlled-release fertilizer (CRF) to reduce NO emissions from urea, applied at a rate of 120 kg ha of N. Two field experiments in ratoon cycle sugarcane were performed in Brazil. The treatments were (i) no N (control), (ii) urea, (iii) urea+DCD, (iv) urea+DMPP, and (v) CRF. Measurements of NO fluxes were performed using static chambers with four replications. The measurements were conducted three times per week during the first 3 mo and biweekly afterward for a total of 217 and 382 d in the first and second seasons, respectively. The cumulative NO-N emissions in the first ratoon cycle were 1098 g ha in the control treatment and 1924 g ha with urea (0.7% of the total N applied). Addition of NIs to urea reduced NO emissions by more than 90%, which did not differ from those of the plots without N. The CRF treatment showed NO emissions no different from those of urea. The results were similar in the second ratoon: the treatment with urea showed NO emissions of 0.75% of N applied N. Application of NIs resulted in a strong reduction in NO emissions, but CRF increased emissions compared with urea. We therefore conclude that both NIs can be options for mitigation of greenhouse gas emission in sugarcane used for bioenergy.

Nitrous oxide emission and nitrogen use efficiency in response to nitrophosphate, N-(n-butyl) thiophosphoric triamide and dicyandiamide of a wheat cultivated soil under sub-humid monsoon conditions

Abstract. A field experiment was designed to study the effects of nitrogen (N) source and urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) or nitrification inhibitor dicyandiamide (DCD) on nitrous oxide (N2O) emission and N use efficiency (NUE) in a sandy loam soil. Six treatments including no N fertilizer (control), N fertilizer urea alone (U), urea plus NBPT (NBPT), urea plus DCD (DCD), urea plus NBPT and DCD (NBPT plus DCD) and nitrate-based fertilizer nitrophosphate (NP) were designed and implemented separately during the wheat growth period. Seasonal cumulative N2O emissions with urea alone amounted to 0.49 ± 0.12 kg N2O-N ha−1 and were significantly (P &lt; 0.05) reduced to 0.28 ± 0.03, 0.31 ± 0.01 and 0.26 ± 0.01 kg N2O-N ha−1 by application of DCD, NBPT and NBPT plus DCD, respectively. Cumulative N2O emissions from NP were 0.28 ± 0.01 kg N2O-N ha−1. A single N2O flux peak was identified following basal fertilization, and DCD and/or NBPT inhibition effects mainly occurred during the peak emission period. The NP application significantly (P &lt; 0.05) increased wheat yield by 12.3% and NUE from 28.8% (urea alone) to 35.9%, while urease and/or nitrification inhibitors showed a slight increase effect. Our results clearly indicated that the application of urea as basal fertilizer, but not as supplemental fertilizer, together with DCD and NBPT is an effective practice to reduce N2O emissions. The application of NP instead of urea would be an optimum agricultural strategy for reducing N2O emissions and increasing crop yield and NUE for wheat cultivation in soils of the North China Plain.

Effect of dicyandiamide (DCD) delivery method, application rate, and season on pasture urine patch nitrous oxide emissions

Here, we report a study which was designed to examine the effect of a nitrification inhibitor dicyandiamide (DCD) on N2O emissions from pasture urine patches. The aspects of DCD use that were studied were delivery method, application rate, and timing of dairy cow urine deposition. Dairy cow urine (700 kg N ha−1) was applied to pasture on a free draining Otorohanga silt loam soil in New Zealand in the autumn and winter of 2013 with DCD applied at different rates (0, 10, 30, and 60 kg ha−1). In the autumn, DCD was delivered to the soil either by mixing DCD with the urine collected from dairy cows or by using urine from cows that had ingested DCD while being kept in a stall. In the winter, only treatments with DCD mixed in urine were used. Total N2O emissions from urine applied in the autumn or the winter were 1.66 or 1.79 kg N2O-N ha−1 year−1, respectively. This resulted in an annual emission factor (EF3, as a percentage of applied urine N lost as N2O-N) of 0.21 and 0.20 %, respectively. The EF3 was reduced equally with either DCD delivery method with the reductions increasing with increasing DCD rate. This indicates that DCD in urine, excreted by cows that are provided DCD-amended feed, can effectively reduce N2O emissions and that a higher DCD rate will be more effective. Further work is required to ensure that DCD applied using this innovative technique is also effective using different feed and animal types under a range of environmental conditions.

Effect of Biochar Application on the Efficacy of the Nitrification Inhibitor Dicyandiamide in Soils

A series of laboratory incubation experiments was conducted to evaluate the effect of biochar application on the efficacy of the nitrification inhibitor (NI) dicyandiamide (DCD) in Cambisol (pH 7.14) and Latosol (pH 4.83). The feedstocks (eucalyptus wood, coconut coir, and rice straw), pyrolysis temperatures (350, 500, and 650 ˚C), and application rates (0.5, 1.0, 2.5, and 5.0% of 200 g soil) were identified as influential factors. The results showed that biochar could significantly reduce the effectiveness of DCD on nitrification inhibition. Biochar produced from eucalyptus wood with a large surface area (426.4 m2 g−1) had the strongest ability to reduce the inhibitory effect of DCD in nearly neutral Cambisol, while biochar from rice straw with a high pH had the greatest influence on acidic Latosol. Increasing pyrolysis temperature and application rates can strengthen the ability of biochar to reduce the inhibitory effect of DCD. Generally, the decrease of the DCD nitrification inhibitory effect on nearly neutral soil was controlled by the surface area of the applied biochar; meanwhile, the rise of soil pH caused by biochar application was also an important influencing factor in acid soil.

Soil aeration affects the degradation rate of the nitrification inhibitor dicyandiamide

Dicyandiamide (DCD) is a nitrification inhibitor of variable efficacy. In soils, DCD biodegradation rate is known to be a function of temperature; however, microbial activity can also be affected by soil aeration and substrate availability. Studies determining the effects of soil aeration on DCD degradation are few. We tested the null hypothesis that the rate of degradation of DCD in soil would be the same under aerobic and anaerobic conditions. Soils from two sites with different organic matter concentrations but the same parent material were sampled to the same depth, sieved, and repacked into tubes (‘soil cores’). These were saturated with a DCD solution (30 µg mL–1) and placed under controlled aeration conditions by imposing five levels of matric potential (0, –1, –3, –6, and –10 kPa) at a constant temperature (22°C). The relative O2 diffusivity (O2 diffusion coefficient in soil/O2 diffusion coefficient in air, Dp/Do) was measured, along with periodic destructive sampling of soil cores over 40 days, to assess the DCD concentrations. Fitting first-order exponential functions to plots of soil DCD concentration v. time showed that the DCD degradation rate was greater (P &lt; 0.05) when the soil was aerobic (Dp/Do ≥ 0.01). Consequently, the null hypothesis was rejected. These results show that soil aeration determines the degradation rate of DCD.