Nitrification Inhibitor Dicyandiamide Research Articles

Comparison of dicyandiamide and biochar for reducing nitrate leaching under winter forage grazing in Canterbury, New Zealand

The presence of nitrate (NO3−) in a water body can contribute to surface water eutrophication and can be harmful to the health of humans. The objective of this study was to determine suitable mitigation options for reducing NO3− leaching losses under dairy winter forage grazing conditions using dicyandiamide (DCD) and biochar in Canterbury, New Zealand. Total NO3−-N leaching losses from urine-treated soil was decreased by 38% from 379 kg NO3−-N ha–1 to 237 kg NO3−-N ha–1 with the addition of DCD. The addition of DCD in combination with biochar to urine-treated soil reduced the total amount of NO3−-N leached by 46% to 203 kg NO3−-N ha–1. However, the application of biochar to urine-treated soil did not significantly affect the total amount of NO3−-N leached. In addition, the urine + DCD and urine + DCD + biochar treatments significantly reduced both the soil NO3−-N concentration and ammonia oxidising bacteria (AOB) amoA gene abundance. However, the urine + biochar treatment had no effect on the abundance of AOB. The nitrification inhibitor DCD was found to be an effective mitigation tool for reducing soil nitrification rate and thus NO3− leaching losses. However, biochar was not effective in reducing NO3− leaching losses at the application rate used in this study.

Use of the nitrification inhibitor dicyandiamide (DCD) does not mitigate N2O emission from bovine urine patches under Oxisol in Northwest Brazil

Animal production systems are important sources of greenhouse gases (GHGs), especially methane (CH4) and nitrous oxide (N2O). GHG emissions from urine patches have been extensively studied in temperate climates, with few studies under tropical conditions. Here we examined the driving factors of N2O and CH4 emission from urine patches in the tropics, as well as the role of the nitrification inhibitor DCD (dicyandiamide) in mitigating emissions. We hypothesized that the high temperature and periodical rainfall can increase GHG emissions from urine patches through accelerating mineralization of urine-N. We measured CH4 and N2O emissions from beef cattle urine (360 kg N ha−1) in Rondonia state (Brazil, tropical climate), during two different seasons (winter and summer), with and without the application of DCD (10 kg ha−1). No effects of DCD on cumulative N2O emissions were detected in summer, but DCD retarded the main emission peak. During winter DCD increased N2O emissions from 10.8 to 39.2 mg N–N2O m−2 (p ≤ 0.05). Emission factors averaged 0.4 % for summer and 0.1 % for winter, which is significantly lower than the IPCC default value of 1 %. The climate, associated with soil (acidic pH, WFPS and low N content) and plant properties (biological nitrification inhibition) resulted in a low emission factor. We concluded that the IPCC default emission factor for tropical systems may be reduced, and that the application of DCD is not recommended in such systems.

Nitrogen leaching losses from lysimeters containing winter kale: the effects of urinary N rate and DCD application

Nitrogen (N) leached from the plant-soil system is an environmental concern. The objective of this study was to quantify N leaching losses from cow urine deposited during grazing of a winter forage crop (kale), and determine the effect of using the nitrification inhibitor dicyandiamide (DCD) to reduce N leaching losses. Fresh cow urine was applied to the surface of large soil monolith lysimeters in late June 2011 at two urinary N deposition rates; 500 and 700 kg N ha−1 (with and without DCD), and compared with losses from lysimeters receiving no urine. Most of the N leaching loss was in the form of nitrate-N (NO3–-N), with an average of 25% leached as ammonium-N (NH4 +-N). Nitrate-N leaching losses were significantly higher under urine-treated lysimeters (213 and 380 kg NO3–-N ha−1 at the 500 and 700 kg N ha−1 rates, respectively) than those without urine (c. 33 kg NO3–-N ha−1). The application of DCD reduced NO3–-N leaching losses by up to 54%. The results indicate that N leaching losses from winter forage crop systems are high and that the application of DCD can reduce these losses.

The effect of the nitrification inhibitor dicyandiamide (DCD) on nitrous oxide and methane emissions after cattle slurry application to Irish grassland

Application of cattle slurry to grassland can lead to gaseous losses of nitrogen (N). The dynamics of ammonia (NH3) emissions are well documented, but emissions of nitrous oxide (N2O) and other trace gases from land application of cattle slurry, are not as well understood. Nitrification inhibitors such as dicyandiamide (DCD) help to retain soil N in the ammonium (NH4+) form, which is expected to result in reduced N loss and increased N use efficiency. Emissions of methane (CH4) could potentially be affected by DCD, since the enzyme ammonia monooxygenase (AMO), which DCD is thought to inhibit, can oxidise CH4 as well as NH3. The objective of this study was to investigate the impacts of DCD on N2O and CH4 emissions from grassland soils after slurry application. At one experimental site, Johnstown Castle (JC), County Wexford, Ireland, slurry was applied in March, June and October for two years, at a rate of 33m3ha−1, by either bandspread (BS) or splashplate (SP) application methods, with and without DCD. A second site at Hillsborough (HB), County Down, Ireland, was treated in the same way for one year only, using the SP application method. Emissions of N2O and CH4 were measured using static chambers. Over the entire experiment DCD significantly reduced cumulative N2O emissions by 47 and 70% at both sites. Slurry spreading method had no significant effect on direct N2O emissions and there was no effect of DCD on CH4 emissions throughout the experiment. Using an emission factor for indirect N2O emissions of 1%, modelled losses of NH3 through volatilisation, resulted in an estimated 13 times greater indirect than direct N2O emissions. The results suggest that, under typical Irish field conditions, DCD can be used to decrease direct N2O emissions, without increasing CH4 emissions, and bandspreading can be used as a method of decreasing NH3 volatilisation, without increasing direct N2O or CH4 emissions. Since direct N2O emissions were relatively small, targeting indirect N2O emissions through mitigation of NH3 volatilisation and nitrate (NO3−) leaching could be an effective way of decreasing total N2O emissions from slurry application at these sites.

Evaluating the effects of dicyandiamide (DCD) on nitrogen cycling and dry matter production in a 3-year trial on a dairy pasture in South Otago, New Zealand

The nitrification inhibitor dicyandiamide (DCD) has been reported to significantly reduce nitrate () leaching and nitrous oxide (N2O) emissions under urine patches in New Zealand trial conditions. However, results on the efficacy of DCD for increasing pasture production have been inconclusive. As part of a national series of nitrous oxide mitigation research (NOMR) trials, a 3-year study was conducted at a dairy farm in South Otago to examine the effect of DCD on pasture production and N leaching under mowing and/or (simulated) grazing conditions and on N2O losses from dung and urine patches. Over the three trial years, DCD significantly inhibited nitrification in urine-amended soil, reducing peak concentrations in the soil by >50% and the N2O emission factor from urine by 33%–72%. Nitrate concentrations in drainage under simulated grazing plots with or without DCD applications were low and consequently no effect of DCD was detected. The N2O emissions and N leaching results suggested that high rates of denitrification occurred in the imperfectly draining soil, particularly in years 2 and 3 of the study. DCD significantly increased spring pasture dry matter (DM) yields from urine patches by 9%–21% in all years under mowing, but no significant annual effect on DM response was detected under either mowing or grazing. The observed increases in DM response in the urine patches under mowing were not detectable under the variable pasture responses under true grazing conditions.

Dicyandiamide (DCD) effect on nitrous oxide emissions, nitrate leaching and pasture yield in Canterbury, New Zealand

A 3-year study was carried out in Canterbury, New Zealand, to determine the effect of a nitrification inhibitor dicyandiamide (DCD) on N2O emissions, nitrate () leaching and pasture yield. In all 3 years, DCD was highly effective in reducing N2O emissions from urine-nitrogen (N) applied in autumn (April and May), decreasing the N2O emission factor by 41%–82%. In addition, DCD consistently reduced -N leaching losses by 48%–69% from the animal urine applied in April. Pasture yield responses to DCD application varied from 0%–17%, probably due to other growth limiting factors and/or the methodology used in the pasture yield measurement. The reductions in leaching are of particular value at this point in time due to the increasingly strict regional council regulations that are being imposed on farmers to reduce N leaching losses.

Effects of the nitrification inhibitor dicyandiamide (DCD) on pasture production, nitrous oxide emissions and nitrate leaching in Waikato, New Zealand

Mowing and grazing studies over 3 years were used to examine the effects of application of the nitrification inhibitor dicyandiamide (DCD) on pasture production, soil nitrogen (N) transformations, nitrous oxide (N2O) emissions and nitrate leaching from dairy pastures in the Waikato region (northern North Island) of New Zealand. In all cases, DCD inhibited nitrification and reduced the amount of nitrate production. Emissions of N2O from pastoral soil receiving cow urine in autumn were reduced by 18%–71% due to DCD application. Lysimeter studies showed a decrease in nitrate leaching from urine due to DCD by up to 74%, but it was dependent on timing and frequency of DCD application. DCD applications between April and June were most effective for reducing nitrate leaching, but timing of applications needs to account for the temperature profile effects on DCD longevity in soil and three applications may be necessary to achieve greatest benefits. In the mowing trial in one year there was a 4% (P < 0.05) increase in pasture growth during the winter/spring period. Otherwise, there was no significant effect of DCD applications (two to five applications per year) on seasonal or annual pasture production. This study indicates that DCD can provide valuable reductions in N emissions to the environment, making it an effective N mitigation option for use on dairy farms in northern North Island regions.

Precipitation but not soil texture alters effectiveness of dicyandiamide to decrease nitrate leaching from dairy cow urine

AbstractThis experiment compared the effectiveness of the nitrification inhibitor dicyandiamide (DCD) in decreasing NO3‐N leaching from dairy cow urine (1000 kg N/ha equivalent). DCD was applied to perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) on three soil types (silt loam, sandy loam and clay) and under two precipitation regimes using intact soil monolith zero tension lysimeters (50 cm diameter by 65 cm deep). Over the two experiment years, annual precipitation (rainfall plus supplemented irrigation) covered the range 1103 to 2351 mm. Soil type affected the forms of N that leached after urine application. Most urea was lost from the clay soil in the first drainage collections after application. Ammonium‐N leached from the sandy soil. Apart from one soil type (sandy loam) giving a nil response to DCD in 1 yr, there was no strong evidence that soil type changed DCD effectiveness (the amount of NO3‐N retained, expressed as a percentage of the NO3‐N leached from untreated urine). Where DCD decreased leaching, effectiveness ranged between 6 and 57% with a mean value of 34 ± 5%. Drainage depth explained 50% of the variation in DCD effectiveness (P &lt; 0.05) and indicated a 7% decrease per 100 mm extra drainage. Extra pasture growth and N uptake were strongly related to the amount of N saved by DCD application. We conclude that there may be scope to use rainfall/drainage as an estimate of likely DCD effectiveness at a site, but further work is required to test this across a wider range of circumstances.

Injection of Dicyandiamide-Treated Pig Slurry Reduced Ammonia Volatilization without Enhancing Soil Nitrous Oxide Emissions from No-Till Corn in Southern Brazil.

There is a lack of information on how placement in soil and nitrification inhibitors affects nitrous oxide (NO) and ammonia (NH) emissions from pig slurry (PS) applied under no-till (NT) conditions. Our objective was to determine the impact of injecting PS and treating it with the nitrification inhibitor dicyandiamide (DCD) on NH and NO emissions from soils under NT in subtropical southern Brazil. The emissions of these gases were compared for shallow (∼ 10 cm) injection and surface broadcasting of PS with and without DCD (8.1-10.0 kg ha; 6.5-8.4% of applied NH-N). Measurements were made at two sites during two summer growing seasons under NT corn crops. Injection reduced NH volatilization by 70% but increased NO emissions 2.4-fold (from 2628 to 6198 g NO N ha) compared with surface broadcast application. Adding DCD to PS inhibited nitrification and reduced NO emissions by an average of 28% (730 g NO-N ha) for surface broadcast and 66% (4105 g NO-N ha) for injection but did not increase NH volatilization. Consequently, NO emission factors were much higher for injection (3.6%) than for surface broadcast (1.3%) application and were reduced (0.9%) when DCD was added to injected PS. In conclusion, the injection of DCD-treated slurry is a recommendable practice for reducing NH and NO emissions when applying PS on NT corn in southern Brazil.

Predicting the efficacy of the nitrification inhibitor dicyandiamide in pastoral soils

Aims Identification of soil, environmental, or microbial properties linked with efficacy of the nitrification inhibitor dicyandiamide (DCD) in high and low-input pastoral farming system soils.

Mitigating Nitrous Oxide Emissions from Corn Cropping Systems in the Midwestern U.S.: Potential and Data Gaps

One of the unintended nitrogen (N)-loss pathways from cropland is the emission of nitrous oxide (N2O), a potent greenhouse gas and ozone depleting substance. This study explores the potential of alternative agronomic management practices to mitigate N2O emissions from corn cropping systems in major corn producing regions in the U.S. and Canada, using meta-analysis. The use of the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) in combination with the nitrification inhibitor Dicyandiamide (DCD) was the only management strategy that consistently reduced N2O emissions, but the number of observations underlying this effect was relatively low. Manure application caused higher N2O emissions compared to the use of synthetic fertilizer N. This warrants further investigation in appropriate manure N-management, particularly in the Lake States where manure application is common. The N2O response to increasing N-rate varied by region, indicating the importance of region-specific approaches for quantifying N2O emissions and mitigation potential. In general, more data collection on side-by-side comparisons of common and alternative management practices, especially those pertaining to N-placement, N-timing, and N-source, in combination with biogeochemical model simulations, will be needed to further develop and improve N2O mitigation strategies for corn cropping systems in the major corn producing regions in the U.S.

Controls of nitrous oxide emission after simulated cattle urine deposition

Urine deposited during grazing is a significant source of atmospheric nitrous oxide (N2O). The potential for N2O emissions from urine patches is high, and a better understanding of controls is needed. This study investigated soil nitrogen (N) dynamics and N2O emissions from cattle urine, and effects of increasing urinary N to 1000kgNha−1 or delaying nitrification by amendment of the nitrification inhibitor dicyandiamide (DCD). Soil N2O concentration profiles and mineral N dynamics were monitored. The study was a randomized block experiment initiated in May 2012, in which urine deposition was simulated in paired field plots to accommodate all measurements. One plot had a pre-installed chamber support for N2O flux measurements. Volumetric water content (VWC) was determined in the same position in both sub-plots, i.e., with and without chamber supports. Plant growth was monitored using ratio vegetation index (RVI). Compared to unamended urine, emissions of N2O were significantly higher with urea-amendment, and lower with DCD amendment, also when expressed as proportions of N applied. Soil mineral N dynamics showed that N2O emissions were closely linked to nitrification activity. There was no close relationship between N2O emissions and concentration profiles of N2O in the soil; instead, emissions were significantly (p<0.05) related to N2O concentrations at 5cm depth. Chamber supports increased water retention in urine-amended soil, but not in reference soil. Based on patterns of mineral N and VWC it is proposed that nutrient retention and higher salinity in the presence of chamber supports increased water retention. This may have implications for the quantification of N2O emissions from urine patches.

Effect of temperature on dicyandiamide (DCD) longevity in pastoral soils under field conditions

Data were analysed from five trials begun in autumn at a field site and a relationship between time for concentration of the nitrification inhibitor dicyandiamide (DCD) in soil to halve (t½, days) and the mean soil temperature (T, °C) was developed: t½=54–1.8T. For example, when T was 8 and 16°C, t½ was 39±6 and 25±3 days (±95% confidence limit), respectively. Previously, under laboratory conditions at equivalent temperatures, the corresponding values of t½ were 86±31 and 44±24days. Thus, the proportional responses of t½ to increasing T from 8 to 16°C were similar, but under field conditions t½ was about half that under laboratory conditions.

Integration of measures to mitigate reactive nitrogen losses to the environment from grazed pastoral dairy systems

SUMMARYThe need for nitrogen (N) efficiency measures for dairy systems is as great as ever if we are to meet the challenge of increasing global production of animal-based protein while reducing N losses to the environment. The present paper provides an overview of current N efficiency and mitigation options for pastoral dairy farm systems and assesses the impact of integrating a range of these options on reactive N loss to the environment from dairy farms located in five regions of New Zealand with contrasting soil, climate and farm management attributes. Specific options evaluated were: (i) eliminating winter applications of fertilizer N, (ii) optimal reuse of farm dairy effluent, (iii) improving animal performance through better feeding and using cows with higher genetic merit, (iv) lowering dietary N concentration, (v) applying the nitrification inhibitor dicyandiamide (DCD) and (vi) restricting the duration of pasture grazing during autumn and winter. The Overseer®Nutrient Budgeting model was used to estimate N losses from representative farms that were characterized based on information obtained from detailed farmer surveys conducted in 2001 and 2009. The analysis suggests that (i) milk production increases of 7–30% were associated with increased N leaching and nitrous oxide (N2O) emission losses of 3–30 and 0–25%, respectively; and (ii) integrating a range of strategic and tactical management and mitigation options could offset these increased N losses. The modelling analysis also suggested that the restricted autumn and winter grazing strategy resulted in some degree of pollution swapping, with reductions in N leaching loss being associated with increases in N loss via ammonia volatilization and N2O emissions from effluents captured and stored in the confinement systems. Future research efforts need to include farm systems level experimentation to validate and assess the impacts of region-specific dairy systems redesign on productivity, profit, environmental losses, practical feasibility and un-intended consequences.

The nitrification inhibitor dicyandiamide increases mineralization–immobilization turnover in slurry-amended grassland soil

SUMMARYNitrification inhibitors are used in agriculture for the purpose of decreasing nitrogen (N) losses, by limiting the microbially mediated oxidation of ammonium (NH4+) to nitrate (NO3−). Successful inhibition of nitrification has been shown in numerous studies, but the extent to which inhibitors affect other N transformations in soil is largely unknown. In the present study, cattle slurry was applied to microcosms of three different grassland soils, with or without the nitrification inhibitor dicyandiamide (DCD). A solution containing NH4+and NO3−, labelled with15N either on the NH4+or the NO3−part, was mixed with the slurry before application. Gross N transformation rates were estimated using a15N tracing model. In all three soils, DCD significantly inhibited gross autotrophic nitrification, by 79–90%. Gross mineralization of recalcitrant organic N increased significantly with DCD addition in two soils, whereas gross heterotrophic nitrification from the same pool decreased with DCD addition in two soils. Fungal to bacterial ratios were not significantly affected by DCD addition. Total gross mineralization and immobilization increased significantly across the three soils when DCD was used, which suggests that DCD can cause non-target effects on soil N mineralization–immobilization turnover.

Improving pasture growth and urea efficiency using N inhibitor, molybdenum and elemental sulphur

A one year field experiment was conducted to assess the efficiency of urea fertilizer applied to pasture near Lincoln University, New Zealand. Urea with or without (±) molybdenum (Mo) were applied to field plot, with a urease inhibitor (N-(n-butyl) thiophosphoric triamide (nBTPT), nBTPT + elemental sulphur (S), and nitrification inhibitor dicyandiamide (DCD) + nBTPT defined as a double inhibitor (DI) in spring 2005. Mo was sprayed at the rate of 50 g Mo/ha/yr once. Urea ± various inhibitor and S treatments were broadcast at a rate of 30 kg N/ha 5 times over one year. The Mo alone treatment increased pasture dry matter (PDM) yield by 8.9%. Molybdenum, when applied together with urea+nBTPT+S, urea+nBTPT and urea alone, caused an initial depression in PDM yield by 14.2, 13 and 5.6% respectively. However, these depressions in yield disappeared from the second pasture cut. Over a one year period, Mo applied with urea+nBTPT, urea+DI and urea+nBTPT+S produced 18179, 16716 and 18253 kg DM ha -1 respectively, compared to 16171 kg ha -1 for urea+Mo. Pastures which

Responses of Ammonia-Oxidizing Bacteria and Archaea in Two Agricultural Soils to Nitrification Inhibitors DCD and DMPP: A Pot Experiment

Taking two important agricultural soils with different pH, brown soil (Hap-Udic Luvisol) and cinnamon soil (Hap-Ustic Luvisol), from Northeast China, a pot culture experiment with spring maize (Zea mays L.) was conducted to study the dynamic changes in the abundance and diversity of soil ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) populations during maize growth period in response to the additions of nitrification inhibitors dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) by the methods of real-time polymerase chain reaction (PCR) assay, PCR-denaturing gradient gel electrophoresis (DGGE), and construction of clone library targeting the amoA gene. Four treatments were established, i.e., no urea (control), urea, urea plus DCD, and urea plus DMPP. Both DCD and DMPP inhibited growth of AOB significantly, compared to applying urea alone. Soil bacterial amoA gene copies had a significant positive linear correlation with soil nitrate content, but soil archaeal amoA gene copies did not. In both soils, all AOB sequences fell within Nitrosospira or Nitrosospira-like groups, and all AOA sequences belonged to group 1.1b crenarchaea. With the application of DCD or DMPP, community composition of AOB and AOA in the two soils had less change except that the AOB community composition in Hap-Udic Luvisol changed at the last two growth stages of maize under the application of DCD. AOB rather than AOA likely dominated soil ammonia oxidation in these two agricultural soils.

The effect of dicyandiamide addition to cattle slurry on soil gross nitrogen transformations at a grassland site in Northern Ireland

SUMMARYMany studies have shown the efficacy of the nitrification inhibitor dicyandiamide (DCD) in reducing nitrous oxide (N2O) emissions and nitrate (NO3−) leaching. However, there is no information on the effect of DCD on gross soil N transformations under field conditions, which is key information if it is to be used as a mitigation strategy to reduce N losses. The current field study was conducted to determine the effect of DCD on ten gross nitrogen (N) transformations in soil following cattle slurry (CS) application to grassland in Northern Ireland on three occasions (June 2010, October 2010 and March 2011).Ammonium (NH4+) oxidation (ONH4) was the dominant process in total NO3−production (ONH4+ONrec(oxidation of recalcitrant organic N to NO3−)) following CS application, accounting for 0·894–0·949. Dicyandiamide inhibited total NO3−production from CS by 0·781, 0·696 and 0·807 in June 2010, October 2010 and March 2011, respectively. The lower inhibition level in October 2010 was thought to be due to the higher rainfall and soil moisture content in that month compared to the other application times. As DCD strongly inhibited NH4+oxidation following CS application, it also decreased the rate of total NO3−consumption, since less NO3−was formed. The rates of mineralization from recalcitrant organic-N (MNrec) were higher than from labile organic-N (MNlab) on all occasions. The DCD significantly increased total mineralization (MNrec+MNlab) following CS application in June 2010 and March 2011, but had no significant effect in October 2010. In contrast, the rate of immobilization of labile organic-N (INH4_Nlab) was higher than from recalcitrant organic-N (INH4_Nrec) on all occasions, accounting for 0·878–0·976 of total NH4+immobilization from CS. The DCD significantly increased total immobilization (INH4_Nrec+INH4_Nlab) when CS was applied in June 2010, but had no significant effect at other times of the year.Dicyandiamide was shown to be a highly effective inhibitor of ammonium oxidation at this grassland site. Although there was evidence that it increased both NH4+mineralization and immobilization following CS application, its effect on these processes was inconsistent. Further work is required to understand the reason for these inconsistent effects: future improvements in15N tracer models may help.

Administration of dicyandiamide to dairy cows via drinking water reduces nitrogen losses from grazed pastures

SUMMARYOral administration of the nitrification inhibitor dicyandiamide (DCD) to ruminants for excretion in urine represents a targeted mitigation strategy to reduce nitrogen (N) losses from grazed pasture. A farmlet grazing study was undertaken to examine the environmental benefits of administering DCD in trough water to non-lactating Friesian dairy cows that consecutively grazed 12 replicated plots (each 627 m2with a grazing intensity of up to 319 cows/ha/day) during two grazing rotations in the winter of 2007 in the Waikato region, New Zealand. Nitrate-N (NO3−-N) leaching losses were measured using ceramic cup samplers (600 mm soil depth) and gaseous emissions of nitrous oxide (N2O) were quantified using a static chamber technique in the DCD and control treatments. Administration of DCD in trough water had no effect on daily water intake by dairy cows, which averaged 15 and 18 l/cow/day for the June and August grazing rotations, respectively. This resulted in a mean daily DCD intake of 46 and 110 g/cow/day, respectively. The DCD farmlet had significantly lower NO3−-N concentrations in leachate at the last three samplings, which reduced total NO3−-N leaching losses by 40% (from 32·0 to 19·2 kg N/ha). The DCD treatment reduced N2O emission rates compared to the control treatment following the August grazing, resulting in a 45% reduction in total N2O emissions relative to the control treatment (from 0·49 to 0·27 kg N2O-N/ha). This preliminary study highlights the potential for administering ruminants with DCD as an effective mitigation option for reducing N losses from agricultural systems.

Effects of the nitrification inhibitor dicyandiamide (DCD) on gross N transformation rates and mitigating N2O emission in paddy soils

The nitrification inhibitor dicyandiamide (DCD, C2H4N4) is effective in suppressing nitrification and N2O emission in many agro-ecosystems. However, whether DCD affects other nitrogen (N) transformation processes, and the mechanisms of its inhibitory effects on N2O emission, are not fully understood. In the present study, we conducted a 15N dilution incubation experiment to investigate the effects of DCD on gross N transformation rates and N2O emissions in two paddy soils under an intensive irrigated rice-upland crop rotation system. The duration of microbial inhibition by DCD was also evaluated. We used the numerical model FLUAZ, based on the 15N tracing technique, to calculate gross N transformation rates. The results showed that DCD could effectively inhibit gross N nitrification in the tested soils; however, no influence on N mineralization and immobilization was detected. Lower N2O emissions from both soils were observed in the presence of DCD, due to the dual functions of DCD on both nitrification rates and the fraction of N2O in nitrification products. While, further study to confirm our results by direct measurement of DCD in reducing the fraction of N2O in nitrification products should be conducted. The inhibitory effect of DCD on gross N nitrification and N2O emission decreased over time, and was not statistically significant four weeks after the addition of this inhibitor to the soils.