Dicyandiamide Treatments Research Articles

Effects of Dicyandiamide on the Accumulation and Leaching Risk of Soil NO<sub>3</sub><sup>-</sup>-N in Aquic Brown Soils

A field experiment was conducted at the vegetable production base of Lixiang town in Shenyang city, Liaoning province to study the effects of dicyandiamide (DCD) application on the accumulation and leaching risk of soil nitrate. The results showed that applying DCD significantly decreased the amount of soil NO3--N in the 0-10cm and 10-20cm soil layers compared to without DCD addition (P < 0.01). However, the difference was not significant in the 20-40cm (P > 0.05). These results indicated that the application of DCD reduced the leaching risk of soil nitrate from topsoil to subsoil. At the 28d of fertilizer application, the amount of soil NO3--N was higher in the NP+M, NP+M+2%DCD and NP+M+5%DCD treatments than in the M, M+2%DCD and M+5%DCD treatments, suggesting that the combined application of chemical fertilizer and organic manure weakened inhibiting effect of DCD on the amount of soil NO3--N.

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 prolonged oral administration of dicyandiamide to dairy heifers on excretion in urine and efficacy in soil

Oral administration of the nitrification inhibitor dicyandiamide (DCD) to grazing ruminants for excretion in urine represents a targeted mitigation strategy to reduce nitrogen (N) losses from grazed pastures. A field trial and allied laboratory incubation study were conducted to examine the effects of oral administration of DCD to non-lactating Friesian dairy heifers on excretion of DCD in urine and efficacy in soil. Dairy heifers were orally administered DCD daily at three treatment levels (low, medium and high; 12, 24 and 36gDCDheifer−1day−1, respectively) and compared to a nil-DCD control group over a 90-day continuous dosing period. There were no adverse effects of DCD administration on heifer health or growth, as inferred by live-weight gain and measured blood metabolite levels. Prolonged administration of DCD to dairy heifers resulted in the sustained excretion of DCD in the urine over 90 days and inhibition of nitrification of urinary-N in the silty peat soil for up to 56 days (incubated at 20°C; P<0.001). Field soil sampling (0–75mm depth) of individual urine patches for DCD analysis revealed that a 3-fold increase in the rate of DCD administered resulted in a similar increase in the concentration of DCD voided in the urine and subsequently deposited in urine patches (median equivalent DCD application rates of 22, 36 and 59kgha−1 for the low, medium and high DCD treatment levels, respectively; P<0.001). However, large differences (up to 40-fold) existed between individual urine patches in the rate of DCD deposited at each treatment level, which showed a positively skewed distribution. This study highlights the viability of prolonged daily administration of DCD to ruminants for sustained excretion in urine and effective inhibition of nitrification in soil as a practical targeted mitigation technology to reduce urinary-N losses from grazed pastures.

Effect of amending cattle urine with dicyandiamide on soil nitrogen dynamics and leaching of urinary-nitrogen

Oral administration of dicyandiamide (DCD) to grazing ruminants for excretion in urine represents an alternative delivery technique to conventional broadcast application of DCD to reduce urinary nitrogen (N) losses from grazed pastures. A field lysimeter trial and an allied plot mowing trial were conducted to examine the effects of intermixing DCD in cattle urine on soil and pasture N dynamics and leaching losses in a free-draining pumice soil. DCD was either intermixed with urine to achieve equivalent application rates of 10, 30 or 60kgDCDha−1, or surface broadcasted as a spray solution (10 or 30kgDCDha−1) onto the soil surface following urine application and compared to controls (urine and nil-controls without DCD). A single application of 15N-labelled artificial cattle urine (equivalent to 600kgNha−1) and corresponding DCD treatments were applied in late autumn and monitored over the following 300 days. DCD altered the partitioning of the applied urine-15N by increasing plant uptake of urinary-N by 32–60% and decreasing urine-15N in leachate, which was primarily influenced by the amount of DCD applied. The method of DCD application had no significant effect on leaching of any N constituent, except for ammonium-N, which was higher in the intermixed relative to the spray DCD treatments (26 vs. 18kgNha−1, respectively; P<0.05). The total amount of nitrate-N leached was reduced from 217kgNha−1 in the urine-control to 143, 80 and 61kgNha−1 (P<0.05) with increasing rates of DCD application of 10, 30 and 60kgha−1, respectively. Application of DCD also significantly (P<0.05) decreased the total amounts of ammonium-N and dissolved organic-N (DON) leached, but led to leaching losses of DCD-N. Rapid and large leaching losses of DCD down the soil profile led to spatial separation from the ammonium-N retained in the surface layer. Leaching of DCD (below 600mm) at 55–69% of that applied represented an important leachable organic-N source (equivalent to 4–27kgNha−1), and reduced the overall efficacy of DCD in decreasing total N leaching losses. The total N leaching losses from all measured N fractions were 332kgNha−1 in the urine-control compared to 236, 157 and 154kgNha−1 at DCD application rates of 10, 30 and 60kgha−1, respectively. This study highlights the potential benefit from delivering DCD in cattle urine to reduce urinary-N leaching losses, with the most effective targeted single application rate being 30kgha−1 under the experimental conditions of this study.

How application timings of urease and nitrification inhibitors affect N losses from urine patches in pastoral system

In intensively dairy-grazed pastoral systems, urine patches are the major source of nitrogen (N) losses via gaseous emissions of ammonia (NH3) and nitrous oxide (N2O) and nitrate (NO3−) leaching. Minimizing these N losses can therefore enable substantial economic and environmental gains. However, the current practice like the blanket application of nitrification inhibitor (NI) such as dicyandiamide (DCD) in suspension form after grazing is not effective at reducing these N losses. The objective of this study was to identify the best time to apply a combination of urease (UI) and NI inhibitors to reduce these N losses from urine patches. A field experiment on Typic Haplustepts silt loam soil, near Lincoln, Canterbury, New Zealand was conducted. The treatments included: a control (no urine or inhibitor), urine alone at 600kgNha−1, and urine with either double inhibitor (DI) in solid form which consists of a mixture (1:7 ratio w/w) of UI (N-(n-butyl) thiophosphoric triamide (nBTPT-trade name Agrotain®) and DCD or DCD alone at 10kgha−1 in suspension form. The DI or DCD was applied to undisturbed lysimeters/field plots 10 and 5 days prior to, the same day, and 5 days after urine application in autumn (May 2008) and again to new lysimeters and field plots in spring (September 2008). Overall there were 10 treatments: control, urine alone and urine with DI or DCD applied at the time of urine application, 5 days before or after urine application and 10 days before urine application. After these treatment applications in 2 seasons, soil ammonium (NH4+) and NO3− concentrations, soil pH, gaseous emissions of NH3 and N2O, and NO3− leaching were monitored for different period of time and pasture growth and N uptake were measured over a year. The DI applied 5 days prior to urine application was more effective in reducing the 3N losses of NH3 volatilization, N2O emissions and NO3− leaching than its corresponding or DCD treatment applied 5 days after urine application. The DI applied 5 days prior to urine application significantly reduced soil NH4+ and NO3− production from applied urine and thus exhibited a minimal increase in soil pH compared with urine alone or with DCD treatments for 4–6 weeks during the two seasons. DCD consistently increased NH3 volatilization when applied 5 or 10 days prior to or concurrently with urine, however it decreased N2O emissions compared to urine alone in both seasons. Applying DI 5 days prior to urine application not only decreased N2O emissions as much as DCD did, it also significantly decreased NH3 volatilization by 38% in autumn and 28% in spring compared to urine alone. Applying DCD or DI in autumn was more effective than spring applications probably because of the lower soil temperature (<10°C) in autumn. Compared to urine alone, DI and DCD applied 5 days prior to urine application in autumn significantly reduced NO3− leaching by 58% and 43%, respectively since the leaching events occurred during the time when these inhibitors were effective (1–2 weeks for nBTPT and 4–6 weeks for DCD). Neither the DI nor DCD had any such significant effect on NO3− leaching losses after their spring application because the leaching events occurred 3–5 months after inhibitor application, which was beyond the time that these inhibitors could be effective. Pasture productivity was only significantly increased by the DI after autumn application, but no significant trend was observed after spring application. These results suggest that DI applied in solid form prior to grazing has the most potential to reduce the 3 key N losses in grazed pastoral system; and it therefore warrants further research to improve its longevity to control N losses for a longer period.

The effect of dicyandiamide on pasture nitrate concentration, yield and N offtake under high N loading in winter and spring

AbstractHigh nitrate () concentrations in pastures and forages represent a health risk to grazing livestock. A field trial was conducted on the Lincoln University Dairy Farm, New Zealand, to investigate the effects of applying the nitrification inhibitor dicyandiamide (DCD) on soil extractable N and pasture concentrations in winter and spring. Treatments were control (T1), urea (T2), urea + DCD (T3), May urine + DCD (T4), August urine + DCD (T5), May urine (T6) and August urine (T7). Urine treatments were applied to the ryegrass‐white clover pasture in either May or August. The DCD treatments were applied at 10 kg DCD ha−1 in May and August and urea at 25 kg N ha−1 at selected intervals. Soil samples (0‐ to 75‐ and 75‐ to 150‐mm horizons) were taken regularly to monitor soil and ammonium () levels. Six pasture harvests were conducted from August 2007 to March 2008 and samples analysed for ‐N concentrations and total N content. Application of DCD significantly (P &lt; 0·001) increased total dry‐matter (DM) production by 39 and 42% for the autumn and spring urine treatments, respectively, compared to the urine‐alone treatments. In addition, the application of DCD also significantly (P &lt; 0·001) increased DM yield by 12% on the urea‐only treatment. DCD significantly (P &lt; 0·001) reduced pasture concentrations in both autumn‐ and spring‐applied urine treatments where DCD was applied. This was directly linked to reductions in soil , and increases in soil , from DCD application. The preferential uptake by pasture for ‐N over ‐N may also have been a contributing factor. DCD application can therefore substantially reduce pasture ‐N concentrations to safe levels under high N‐loading (urine patch) conditions.

Gaseous emissions of N2O and NO and NO3− leaching from urea applied with urease and nitrification inhibitors to a maize (Zea mays) crop

Urea has become the predominant source of synthetic nitrogen (N) fertilizer used throughout the world. Among the various available mitigation tools, urease inhibitors like NBPT have the most potential to improve efficiency of urea by reducing N losses, mainly via ammonia volatilization. However, there is a lack of information on the effect of N-(n-butyl) thiophosphoric triamide (NBPT) on other N losses such as gaseous emissions of N2O and NO and NO3− leaching. A two-year field experiment using irrigated maize (Zea mays) crop was carried out under Mediterranean conditions to evaluate the effectiveness of urea coated with NBPT (0.4%, w/w) alone and with both NBPT and nitrification inhibitor dicyandiamide (DCD) (0.4 and 3%, w/w, respectively) to mitigate N2O–N, NO–N and NO3−–N losses. The different treatments of U, U+NBPT and U+NBPT+DCD were applied to the maize crop in 2009 and then in 2010. The 2010 maize crop followed a fallow period, during which the 2009 crop residues were incorporated into the soil. Two different irrigation regimes were followed each year. In 2009, irrigation was controlled for the first 2 weeks following urea fertilization; whereas, the 2010 crop period was characterized by increased irrigation in the same period. After each treatment application, measurements of the changes in soil mineral N, gaseous emissions of N2O and NO, nitrate leaching and biomass production were made. N2O emissions were effectively abated by NBPT and NBPT+DCD and were reduced by 54 and 24%, respectively, in 2009. A reduction in nitrification rate by the inhibitors was also observed during 2009. In 2010 cropping period, NBPT reduced N2O emissions by 4%; while the combination of NBPT and DCD treatment reduced N2O emission by 43%. Yield-scaled N2O emissions were reduced by 50 and 18% by NBPT and the mixture of NBPT+DCD, respectively, in 2009. Applying inhibitors did not have any significant effect on yield-scaled N2O emissions in the 2010 crop period. Total NO losses from urea were 2.25kgNO–Nha−1 in the 2009 crop period and 5 times lower in the following year; this may provide an indicator of the prevalence of nitrification as the main process in the production of N2O in the 2009 maize crop. Most of the NO3− was lost within the fallow period (i.e. 92, 81 and 75% of the total NO3− leached for U, U+NBPT and U+NBPT+DCD, respectively), so the incorporation of crop residues was not as effective as expected at reducing these N losses. Our study suggests that the effectiveness of NBPT and combination of NBPT+DCD in reducing N losses from applied urea is influenced by management practices, such as irrigation, and climatic conditions.

Effect of the nitrification inhibitor dicyandiamide (DCD) on microbial communities in a pasture soil amended with bovine urine

Nitrification inhibitors, such as dicyandiamide (DCD), have been shown to decrease leaching from urea- and ammonium-based fertilisers and from urine patches in grazed pastures. To date there have been few studies on effects of nitrification inhibitors on non-target soil microbiota. This pot trial examined the short-term effects of DCD on the activity and diversity of both target (ammonium-oxidising bacteria and archaea) and non-target soil microbial populations. Bovine urine at a rate equivalent to 600 kg urine-N ha −1 with or without DCD at 30 kg ha −1 was applied to pots planted with perennial ryegrass. This rate of DCD was typical of the amount applied to pasture in New Zealand, although this annual rate may be spread over several applications carried out over 2–3 months. The single high rate application was used to provide a “worst case scenario” to assist detection of potential impacts of DCD application to non-target soil microflora. Treatments also included DCD alone and untreated control pots. Soil used was a Horotiu sandy loam and pots were maintained at 80% WHC in a controlled-environment room at 12 °C/16 h (day) and 8 °C/8 h (night). Soil mineral N, hot water extractable C and N concentrations, soil pH, microbial biomass C and N, and DCD persistence were measured at regular intervals. Diversity and composition of the overall soil bacterial community were analysed by serial analysis of ribosomal sequence tags (SARST). Effects on ammonium-oxidising bacterial and archaeal communities were monitored more closely by determining the size of these populations using real-time PCR and their transcriptional activity by comparing RNA-denaturing gradient gel electrophoresis (DGGE) profiles following RT-PCR of the amoA gene. Changes in soil pH and mineral N following application of urine in the pot trial reflected patterns typically demonstrated in the field. Application of DCD to soil did not change the diversity of the soil bacterial community, with the four predominant phyla (Proteobacteria, Actinobacteria, Acidobacteria and Firmicutes) remaining in proportions that were similar to control soils. In contrast, urine application to soil resulted in a significant increase in members of Firmicutes, some of which are relatively stress tolerant. In line with the SARST results, shifts in the structure of the active component of the general soil bacterial community were detected in the urine and urine + DCD treatments only, further suggesting DCD had little impact on the overall soil bacterial activity. In contrast the microbes targeted by DCD, the ammonium-oxidising bacteria, were significantly affected by DCD with reductions in population size and altered activity. Ammonium-oxidising archaea, however, showed no response to application of DCD to soil, and were only minimally affected by application of urine. The results suggest that application of DCD to pasture is a relatively benign intervention that has an important role to play in mitigating the environmental hazards imposed by ongoing land use intensification.

A lysimeter study of nitrate leaching from grazed grassland as affected by a nitrification inhibitor, dicyandiamide, and relationships with ammonia oxidizing bacteria and archaea

AbstractNitrate (NO3−) can contribute to surface water eutrophication and is deemed harmful to human health if present at high concentrations in the drinking water. In grazed grassland, most of the NO3−‐N leaching occurs from animal urine‐N returns. The objective of this study was to determine the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO3− leaching in three different soils from different regions of New Zealand under two different rainfall conditions (1260 mm and 2145 mm p.a.), and explore the relationships between NO3−‐N leaching loss and ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA). The DCD nitrification inhibitor was found to be highly effective in decreasing NO3−‐N leaching losses from all three soils under both rainfall conditions. Total NO3−‐N leaching losses from the urine patch areas were decreased from 67.7–457.0 kg NO3−‐N/ha to 29.7–257.4 kg NO3−‐N/ha by the DCD treatment, giving an average decrease of 59%. The total NO3−‐N leaching losses were not significantly affected by the two different rainfall treatments. The total NO3−‐N leaching loss was significantly related to the amoA gene copy numbers of the AOB DNA and to nitrification rate in the soil but not to that of the AOA. These results suggest that the DCD nitrification inhibitor is highly effective in decreasing NO3− leaching under these different soil and rainfall conditions and that the amount of NO3−‐N leached is mainly related to the growth of the AOB population in the nitrogen rich urine patch soils of grazed grassland.

The mitigation potential of hippuric acid on N 2O emissions from urine patches: An in situ determination of its effect

Previous laboratory studies have demonstrated that hippuric acid, a ruminant urine constituent, can mitigate nitrous oxide (N 2O) emissions from simulated urine patches. Hippuric acid has the potential to be a N 2O mitigation tool because animal diets can be manipulated to adjust its concentration in the urine. This study was conducted to determine if the effect observed in previous laboratory studies would also occur in situ under field conditions. In our field study, plots were treated with unadulterated bovine urine (56 mM hippuric acid), the same bovine urine amended with either benzoic acid (34 mM), dicyandiamide (DCD) or varying rates of hippuric acid (up to 90 mM). Soil inorganic-N, N 2O fluxes, and plant N responses were monitored over a 78 d period. Effects on microbial communities were monitored by determining the size and structure of nitrite oxidizer ( nxrA) and nitrite reducer ( nirS) bacterial populations using real-time PCR and denaturing gradient gel electrophoresis (DGGE), respectively. Decreases in N 2O emissions, with increasing hippuric and benzoic acid concentrations, were only seen on Day two of the trial. With the exception of the DCD treatment (0.60% of N applied) the amended urine treatments did not significantly affect emissions of N 2O as a percentage of N applied (1.28–1.65%). Soil inorganic-N and plant response were not affected by urinary amendment, except in the DCD treatment where nitrification inhibition occurred. Nitrite oxidizer community structures shifted and increased approximately 5.4-fold in size over 48 d in response to urine, although no specific response to elevated hippuric acid or benzoic acid was observed. No treatment effects were observed on community structure of the nitrite reducing bacteria but averaged over time the highest rate of hippuric acid significantly decreased nirS gene copy numbers g −1 soil. We concluded that under the conditions of this field study, increasing hippuric or benzoic acid concentrations in bovine urine had no effect on N 2O mitigation in situ. We argue that the discrepancy with previous laboratory studies may be related to differences in soil pH, microbial communities and the presence of vegetation. Further research is needed to determine the potential for hippuric acid as a tool to mitigate N 2O emissions, and its effect(s) on resident N cycling microorganisms.

The effectiveness of a granular formulation of dicyandiamide (DCD) in limiting nitrate leaching from a grazed dairy pasture

The effectiveness of a granular formulation of dicyandiamide (DCD) in limiting nitrate leaching from a grazed dairy pasture in southern New Zealand is reported. Treatments were an untreated Control managed as standard farm practice, and+DCD with two or three applications of DCD per annum at a rate of 10 kg active ingredient (a.i.) ha‐1 per application. Each treatment had hydrologically‐isolated plots 12 m wide × 15m long with separate mole‐pipe drainage systems from which drainage waters were collected and analysed for nitrate and ammonium over a 4‐year period. Pasture production, grass N uptake, grass nitrate‐N concentrations and DCD losses in drainage were also measured over this period. The application of DCD showed a clear and consistent trend in reducing concentrations of nitrate‐N in autumn and early winter drainage. On an annual basis, the application of DCD reduced the amounts of N lost in drainage by between 21 and 56%, depending on the year of study. Calculated mean annual losses of nitrate‐N in drainage over the 4‐year period were 12.9 kgNha‐1 from the control and 6.8 kg N ha‐1 from the DCD treatments (P < 0.05), with the greatest losses in the May‐July period. The application of DCD had no significant effect on annual or seasonal pasture production across all measurement years, with pasture yields in the DCD‐treated plots being less than 1% greater than those observed in the control plots. The application of DCD had little consistent effect on the botanical composition of the sward. Cost‐benefit analysis suggests that the small pasture responses observed at this site would not cover the costs of applying DCD unless there were additional benefits such as a carbon credit for reduced nitrous oxide emissions. The application of DCD had the additional benefit of lowering grass nitrate‐N concentrations on 22 of the 31 measurement dates. Between 2 and 16% of the DCD applied annually to the +DCD treatment was lost in drainage, representing c. 7% of applied DCD over the 4 years of measurement. Based on measured soil temperatures at this site and the observed monthly pattern of N loss in drainage, it is suggested that the scheduling of two autumn applications of DCD (e.g., at the March and May grazings) is the most effective strategy for minimising N losses in drainage at this site.

Effect of rate and form of dicyandiamide application on nitrate leaching and pasture production from a volcanic ash soil in the Waikato

Animal urine has been identified as the main source of nitrate leaching from grazed pastures. The nitrification inhibitor dicyandiamide (DCD) can potentially reduce nitrate leaching losses and increase pasture utilisation of nitrogen (N) from urine. A mowing trial was established on a sandy loam (Typic Orthic Allophanic) soil in the Waikato region to examine the effect of liquid and granular forms of DCD, applied in May at rates of 0, 7, 14 and 28 kg ha‐1, on the fate of urea applied at 600 kg N ha‐1 in artificial urine. The DCD treatments increased pasture production over 211 days by an average of 15% (P < 0.001) and there was no significant effect of rate or form of DCD. Soil sampling 76 days after treatment application showed greater amounts of ammonium remaining in the top 450 mm of soil in the DCD treatments (average ammonium‐N for all DCD treatments of 93 kg N ha‐1 compared with 43 kg N ha‐1 for the urine‐only treatment). Total inorganic N in the top 600 mm of soil at the final (118 day) sampling showed a linear response to DCD application rate (113–190 kg ha‐1 from lowest to highest rate; P < 0.05) and the liquid DCD tended to retain more inorganic‐N than the granular DCD (179 and 131 kg ha‐1, respectively; P < 0.1). Averaged across all DCD treatments, 37% of the applied DCD was measured in the top 450 mm of soil at the day 48 sampling and most of that DCD was found below 150 mm. Leaching of N was measured using ceramic cup samplers at 600 mm depth in the 14 kg DCD ha‐1 treatments and showed that DCD reduced nitrate leaching by 24% from 275 to 208 kg ha‐1 (P < 0.01), with no significant effect of DCD form. Thus, DCD in both liquid and granular forms proved effective in reducing nitrate leaching from urine, indicating its potential for N loss mitigation in grazed pastures.

Influence of dicyandiamide on nitrogen transformation and losses in cow-urine-amended soil cores from grazed pasture

In New Zealand, urine deposited by grazing animals represents the largest source of nitrogen (N) losses, as gaseous emissions of ammonia (NH3) and nitrous oxide (N2O), and leaching of nitrate (NO3−).We determined the effect of dicyandiamide (DCD) on gaseous emissions from pasture with increasing rates of urine-N application, mineral N transformations and potential leaching of N using undisturbed soil cores of Manawatu sandy loam at field capacity. The treatments included four levels of urine-N applied at 0 (control), 14.4, 29.0 and 57.0 g N/m2 with and without DCD at 2.5 g/m2. Results showed a significant (P &lt; 0.05) increase in NH3 and N2O-N emissions as urine application was increased. The addition of DCD to corresponding urine treatments reduced N2O emissions by 33, 56 and 80%, respectively. The addition of DCD with urine to the intact soil cores at field capacity moisture content resulted in a significant increase in the soil ammonium-N (NH4+-N) concentration but little change in NH3 emissions. Addition of DCD to urine reduced potential NO3−-N leaching by 60–65% but potential NH4+-N leaching increased by 2–3.5 times. There was no difference in pasture dry matter production with and without DCD treatments.

Effect of timing and formulation of dicyandiamide (DCD) application on nitrate leaching and pasture production in a Bay of Plenty pastoral soil

Urine excreted from grazing animals has been identified as the main source of nitrate leaching from grazed pastures. The nitrification inhibitor dicyandiamide (DCD) has the potential to be an important tool for reducing nitrate leaching in grazed pasture systems. A mowing trial near Rotorua examined the effects of different DCD formulations, and the timing of DCD application on plant growth and leaching of urine‐N. Treatments were urine‐only or urine+DCD (either granular or liquid DCD) applied at a rate of 18 kg DCD ha‐1. The effect of timing of DCD application was tested by applying the DCD to plots in May (autumn) or July (winter) immediately after urine was applied. The application rate of the urine was equivalent to 598 kg N ha‐1 in the form of artificial urine. There was no significant effect of DCD formulation (granular versus liquid) on any N leaching or yield parameter measured in either the autumn or winter application. On average, the autumn application of DCD significantly (P < 0.001) increased pasture dry matter (DM) from urine plots (34% increase or 21 DM ha‐1). Extrapolation of treatments with or without DCD to grazed pasture, with 5% of the area affected by urine at this grazing, would equate to an annual pasture response of approximately 7%. The increased pasture growth resulted in a greater apparent recovery of urine‐N in herbage from the urine+DCD treatments compared with the urine‐only treatment over the first 98 days of the study of 64% or 103 kg N ha‐1. In contrast to autumn application, winter application of DCD did not significantly influence pasture DM yield from urine plots. Total nitrate leaching losses for the autumn‐applied urine+DCD treatments were 17% less than the urine‐only treatments, but this was not significant. Interestingly, over the short‐term (30–55 days), the autumn urine+DCD treatments showed reduced nitrate leaching losses of up to 50% (P < 0.05), but after day 84 greater amounts of nitrate were leached from the urine+DCD plots giving cumulative losses at day 159 of 217 and 263 kg nitrate‐N ha‐1 for the urine+DCD and urine‐only treatments, respectively. It was apparent that the DCD had become ineffective in inhibiting nitrification, thus allowing the conversion of ammonium to nitrate and its subsequent leaching from the root zone. In contrast to autumn, the application of DCD in winter led to a reduction in nitrate leaching from urine‐N of 62% compared to the urine‐only treatment (average of 32 versus 86 kg N ha‐1 respectively; P < 0.001). Overall, our study showed that when applied at a rate of 18 kg ha‐1 the form of DCD (granular versus liquid) used was inconsequential. However, to gain the greatest benefit from DCD use, more than one application is needed during autumn/winter to maximise the potential for reducing nitrate leaching during this key period of high drainage and N losses.

Effects of the nitrification inhibitor dicyandiamide on soil mineral N, pasture yield, nutrient uptake and pasture quality in a grazed pasture system

AbstractRecent lysimeter studies have demonstrated that the nitrification inhibitor, dicyandiamide (DCD), can reduce nitrate (NO) leaching losses from cow urine patches in grazed pasture systems. The objective of this study was to quantify the effects of fine particle suspension (FPS) DCD on soil mineral N components, pasture yield, nutrient uptake and pasture quality under grazed pasture conditions. A field study was conducted on the Lincoln University dairy farm, Canterbury, New Zealand, from 2002 to 2006. FPS DCD was applied to grazed pasture plots at 10 kg ha−1 in early May in addition to applied cow urine patches at a nitrogen (N) loading rate of 1000 kg N ha−1, with DCD reapplied in early August. Soil mineral N levels in the urine patches were monitored. Pasture yield, N and cation concentrations and uptake were measured in treatment urine patches and inter‐urine areas of the pasture. Comparisons were made with control plots which did not receive DCD. NO levels under the DCD‐treated urine patches (0–7.5 cm) were in the order of 10 kg N ha−1 compared with 40–80 kg N ha−1 under untreated patches, and soil ammonium (NH) levels were consistently higher under the DCD‐treated patches. The DCD significantly and consistently increased pasture yield in both the urine patches, and inter‐urine areas of the pasture in all 4 years of the trial. Mean annual dry matter (DM) yields over 4 years were inter‐urine areas, 10.3; inter‐urine + DCD, 12.4; urine, 12.4 and urine +DCD 16.0 t DM ha−1, representing an average DM yield increase of 20 and 29% in inter‐urine and urine patch areas, respectively. On a whole paddock basis, the increase in annual DM yield resulting from DCD application was estimated to be 21%. N, calcium (Ca), magnesium (Mg) and potassium (K) concentrations in pasture were unaffected by treatment with DCD; however, total annual uptake of these nutrients by pasture was significantly higher in all years where DCD had been applied. Pasture DM, protein, carbohydrate, metabolizable energy and fibre levels and sward clover content were not affected by treatment with DCD. The results demonstrate the agronomic value of the DCD treatment in addition to the environmental benefits in a grazed pasture system.

Modelling DCD effect on nitrate leaching under controlled conditions

Effects of nitrogen losses through nitrate leaching are one of the major environmental issues worldwide. To determine the potential effect of dicyandiamide (DCD), a nitrification inhibitor, on the transformation of urea nitrogen and subsequent nitrate leaching, incubation and column leaching experiments were performed. Tokomaru silt loam soil was treated with urea, DCD, or urea plus DCD. A control was also used. In the laboratory incubation experiment, the conversion of urea to ammonium (i.e. ammonification process or urea hydrolysis) occurred within a day, thereby increasing the soil pH from 5.8 to 6.9. DCD did not affect the ammonification process. However, DCD did slow down the subsequent oxidation of ammonium to nitrate (i.e. nitrification process). The half-life time of ammonium in this soil was increased from 9 days for the urea treatment to 31 days for the urea + DCD treatment. The production of nitrate was 5 times slower when DCD was added. In the leaching experiments, half the columns were leached after 1 day of incubation (Day 1), the other half 7 days later (Day 7). For Day 1, no significant differences in nitrate leaching could be seen between the treatments, as the nitrification had not yet taken place. For Day 7, DCD decreased nitrate leaching by 71% with a corresponding decrease in nitrate-induced cation leaching, including ammonium. Thus, DCD seems to be effective in decreasing both ammonium and nitrate leaching, but its high solubility and thus mobility could be a limitation to its use. The convection–dispersion equation, including source–sink terms for nitrogen transformations, ammonification, and nitrification rate constants, and a factor for nitrification inhibition by DCD, accounting for degradation and efficiency of DCD, could be used reasonably well to simulate nitrate leaching from the column leaching experiments. However, model parameter values for nitrification rate, and efficiency and decay rate for DCD, were different from those obtained from the incubation experiments, which was probably because of the difference in water content of soil between the incubation and leaching experiments.

Ammonia and nitrous oxide emissions from two acidic soils of Nova Scotia fertilised with liquid hog manure mixed with or without dicyandiamide

Gaseous nitrogen (N) loss from field-applied manure in the form of ammonia (NH 3) and nitrous oxide (N 2O) has negative agronomic, environmental and health implications. This study was undertaken to evaluate the combined effect of soil type and dicyandiamide (DCD) on NH 3 and N 2O emissions following application of liquid hog manure. Soil samples (100 g) were placed in 500 mL screw-top Mason-jars and de-ionised water was added to bring the soil samples to 50%, 70% and 90% water-filled pore space (WFPS). Slurry and slurry + DCD treatments were applied at a rate of 116 000 l ha −1. The jars were then sealed and incubated at 21 °C for 21 d. Ammonia volatilisation was quantified using boric acid traps while N 2O gas concentrations were analysed using gas chromatography. Results showed that DCD had no effect ( p > 0.05) on either NH 3 or N 2O emissions. However, soil type had a significant effect ( p < 0.05) on both gases. Overall, the Pugwash soil produced 3 and 2.5 times more NH 3 and N 2O, respectively, than the Acadia soil. N 2O emissions from both soils increased with an increase in %WFPS, indicating that during the spring and fall in Atlantic Canada, when soils are generally wet, a significant amount of N 2O may be emitted from these soils. The relationship between cumulative N 2O and %WFPS was best described by an exponential function R 2 = 0.83 and p < 0.05 (both soils). Therefore, soil type should be taken into consideration when formulating N 2O emission factors. The addition of DCD together with slurry may not be a viable strategy to mitigate N 2O emissions from acidic soils. To reduce emissions of both gases, livestock slurry should not be applied on wet soils.

Mineral nitrogen in a rhizosphere soil and in standing water during rice (Oryza sativa L.) growth: effect of hydroquinone and dicyandiamide

Inhibitors are applied to improve the efficiency of N fertilizer use and to reduce N losses from the soil. However, little information is available on the effects of a urease inhibitor, hydroquinone (HQ), and a nitrification inhibitor, dicyandiamide (DCD), on urea-derived mineral N in the rhizosphere of rice plants and in the standing water. Furthermore, this is important to understand the contribution of rice plants to gaseous N losses in the presence of inhibitor(s). A rhizobox was used to simultaneously study urea-derived mineral N in the soil at increasing distances from rice roots, and the effect of growing plants on the behavior of fertilizer-N in soil. The combined application of urea (U) with DCD showed a significantly positive effect on rice growth. The redox potentials in the rhizosphere soil were higher in the presence than in the absence of DCD, especially when rice plants entered their vigorous growth stage. During the entire experimental period, NH 4 + –N concentrations in the rhizosphere of rice plants were smaller in the U + DCD and U + HQ + DCD treatments than in the U and U + HQ treatments. On days 20 and 60 after fertilization, the U + DCD and U + HQ + DCD treatments showed a smaller concentration of (NO 3 − + NO 2 − )–N in soil less than 0.5 cm from the rhizobox, compared to the U treatment. During the early period of rice growth, the NH 4 + –N concentration of the standing water was higher in the presence than in the absence of DCD. However, there were no significant differences in NH 4 + –N among all treatments after 20 days. In the absence of rice plants, also, the application of DCD and especially DCD and HQ, always increased the level of NH 4 + –N and pH in the standing water. Thus, rice plants might reduce potential gaseous N losses from a urea-fertilized, flooded soil, due to the stimulating effect on rice growth in the presence of DCD or DCD + HQ. The N 2 O emissions from the urea-fertilized, rice-planted soil significantly decreased when DCD or DCD + HQ was used. From the results obtained, we conclude that DCD and DCD + HQ together with U can be an effective tool to improving crop growth and reducing N loss as N 2 O in rice cultivation, and that the use of a rhizobox is useful to study the interaction between plant uptake and the behavior of fertilizer-N in soil.

Nitrogen Transformations in a Chinese Aquic Cambisol Applied Urea with Dicyandiamide or Plant Residues

Understanding the effects on nitrogen (N) transformations and supply to crops of dicyandiamide (DCD) and the various plant residues applied with N fertilizer in China is vital for maximizing crop yields and minimizing environmental pollution. Nitrogen transformations were measured in a Chinese Aquic Cambisol following the application of urea (U), or U with DCD, wheat straw (WS), alfalfa straw (AS), and poultry manure (PM) by aerobic incubation in the laboratory. Nitrification was rapid in the 7 days after U or U with WS, AS, and PM were applied; almost all the applied N from U was nitrified by the 14th day, but only 20% by the 35th day, where DCD was applied with the U. The NH4-N concentrations in the soil with U + DCD was always much higher than those in the other treatments. The results thus showed that DCD significantly inhibited nitrification on this soil. The high C:N ratio of WS significantly decreased the amount of Nmin (NH4-N plus NO3-N) in soil, while the low C:N ratio of AS and PM significantly increased Nmin compared with the U treatment. The content of Norg (organic N extracted by 0.01 M CaCl2 solution) in the soil was much lower than that of Nmin and was not significantly different between the treatments, except for the U + DCD treatment, where it measured as DCD. The N recovery and loss rate after 35 days' incubation, as measured by 15N tracer, was not significantly different in the U, U + WS, U + AS, and U + PM treatments, but recovery was significantly higher and loss correspondingly smaller when DCD was applied. With DCD, the N fertilizer was mostly fixed in soil after 35 days but without DCD was present as NO3-N. For effective use of fertilizers in the North China Plain, an understanding of the effects of applying inhibitors such as DCD and plant residues is needed.

Urease and nitrification inhibitors to reduce emissions of CH4 and N2O in rice production

Strategies used to reduce emissions of N2O and CH4 in rice production normally include irrigation management and fertilization. To date, little information has been published on the measures that can simultaneously reduce both emissions. Effects of application of a urease inhibitor, hydroquinone (HQ), and a nitrification inhibitor, dicyandiamide (DCD) together with urea (U) on N2O and CH4 emission from rice growing were studied in pot experiments. These fertilization treatments were carried out in the presence and absence of wheat straw, applied to the soil surface. Without wheat straw addition, in all treatments with inhibitor(s) the emission of N2O and CH4 was significantly reduced, as compared with the treatment whereby only urea was applied (control). Especially for the U+HQ+DCD treatment, the total emission of N2O and CH4 was about 1/3 and 1/2 of that in the control, respectively. In the presence of wheat straw, the total N2O emission from the U+ HQ+ DCD treatment was about 1/2 of that from the control. The total CH4 emission was less influenced. Wheat straw addition, however, induced a substantial increase in emissions of N2O and CH4. Hence, simultaneous application of organic materials with a high C/N ratio and N-fertilizer (e.g. urea) is not a suitable method to reduce the N2O and CH4 emission. Application of HQ+DCD together with urea seemed to improve the rice growth and to reduce both emissions. The NO3-- N content of the rice plants and denitrification of (NO3- +NO2-)-N might contribute to the N2O emission from flooded rice fields.