Nitrous oxide emissions from dairy farm effluent applied to a New Zealand pasture soil

A field experiment on permanent ryegrass–white clover pasture at AgResearch's Ruakura dairy farm near Hamilton, New Zealand quantified nitrous oxide (N₂O) emissions from different types of dairy effluent applied to soil at three seasons and evaluated the potential of dicyandiamide (DCD) (a nitrification inhibitor) to decrease gaseous N₂O emissions. Fresh or stored manure and farm dairy effluent (FDE; from dairy shed washings), with or without DCD (10 kg/ha), were applied at approximately 100 kg N/ha to plots on a well‐drained soil on volcanic parent material. A field chamber technique was used to measure N₂O emissions. Application of manure or FDE, both in fresh and stored forms, to pasture generally increased N₂O emissions. Overall N₂O emission factors (EF) varied between 0.01% and 1.87%, depending on application season and effluent type. EFs in spring and autumn were greater than those in summer (P < 0.05). Among the effluents, N₂O EFs were largest from fresh FDE (1.65%) during the spring measurement period, stored manure (1.87%) during the autumn and stored FDE (0.25%) during the summer. DCD was effective in decreasing N₂O EFs from fresh FDE, fresh manure, stored FDE and stored manure by 40–80%, 69–76%, 24–84% and 60–70%, respectively. DCD reduced N₂O emissions during the spring and autumn seasons more effectively than in the summer season.     

Reducing NH3, N2O and {\text{NO}}_3^ - –N losses from a pasture soil with urease or nitrification inhibitors and elemental S-amended nitrogenous fertilizers

A 3-month field experiment comparing nitrogen (N) losses from and the agronomic efficiency of various N fertilizers was conducted on a sandy loam (Typic Hapludand) soil at Ruakura AgResearch farm, Hamilton, New Zealand during October to December 2003. Three replicates of seven treatments: urea, urea + the urease inhibitor N-(n-butyl) thiophosphoric triamide (trade name Agrotain), urea + Agrotain + elemental sulphur (S), urea + double inhibitor [DI; i.e., Agrotain + dicyandiamide (DCD)], diammonium phosphate (DAP), DAP + S, each applied at 150 kg N ha⁻¹, and control (no N). After fertilizer application, soil ammonium () and nitrate () concentrations (7.5-cm soil depth), ammonia (NH₃) volatilization, nitrate () leaching, nitrous oxide (N₂O) emission, pasture dry matter, and N uptake were monitored at different timings. Urea applied with Agrotain or Agrotain + S delayed urea hydrolysis and released soil at a slower rate than urea alone or urea + DI. Urea applied with DI increased NH₃ volatilization by 29% over urea alone, while urea + Agrotain and urea + Agrotain + S reduced NH₃ volatilization by 45 and 48%, respectively. Ammonia volatilization losses from DAP were lower than those from urea with or without inhibitors. Total reduction in leaching losses for urea + DI and urea + Agrotain compared to urea alone were 89% and 47%, respectively. Application of S with urea + Agrotain reduced leaching losses by an additional 6%. Nitrous oxide emissions were higher from the DAP and urea alone treatments. Urea applied with DI and urea + Agrotain reduced N₂O emissions by 37 and 5%, respectively, over urea alone. Compared to urea alone, total pasture production increased by 20, 17, and 15% for urea + Agrotain + S, urea + Agrotain, and urea + DI treatments, respectively, representing 86, 71, and 64% increases in N response efficiency. Total N uptake in urea + Agrotain, urea + Agrotain + S, and urea + DI increased by 29, 22, and 20%, respectively, compared to urea alone. These results suggest that the combination of both urease and nitrification inhibitors may have the most potential to reduce N losses and improve pasture production in intensively grazed systems.     

Nitrification Inhibitor,Fertilizer Rate,and Temperature Effects on Nitrous Oxide Emission and Nitrogen Transformation in Loamy Sand Soil

An incubation study investigated the effects of nitrification inhibitors (NIs), dicyandiamide (DCD), and neem oil on the nitrification process in loamy sand soil under different temperatures and fertilizer rates. Results showed that NIs decreased soil nitrification by slowing the conversion of soil ammonium (NH₄⁺)-nitrogen (N) and maintaining soil NH₄⁺-N and nitrate (NO₃^?)-N throughout the incubation time. DCD and neem oil decreased soil nitrous oxide (N₂O) emission by up to 30.9 and 18.8%, respectively. The effectiveness of DCD on reducing cumulative soil N₂O emission and retaining soil NH₄⁺-N was inconsistently greater than that of neem oil, but the NI rate was less obvious than temperature. Fertilizer rate had a stronger positive effect on soil nitrification than temperature, indicating that adding N into low-fertility soil had a greater influence on soil nitrification. DCD and neem oil would be a potential tool for slowing N fertilizer loss in a low-fertility soil under warm to hot climatic conditions.     

Nitrous oxide emissions from two dairy pasture soils as affected by different rates of a fine particle suspension nitrification inhibitor, dicyandiamide

In grazed pasture systems, a major source of N₂O is nitrogen (N) returned to the soil in animal urine. We report in this paper the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), applied in a fine particle suspension (FPS) to reduce N₂O emissions from dairy cow urine patches in two different soils. The soils are Lismore stony silt loam (Udic Haplustept loamy skeletal) and Templeton fine sandy loam (Udic Haplustepts). The pasture on both soils was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). Total N₂O emissions in the Lismore soil were 23.1–31.0 kg N₂O-N ha⁻¹ following the May (autumn) and August (late winter) urine applications, respectively, without DCD. These were reduced to 6.2–8.4 kg N₂O-N ha⁻¹ by the application of DCD FPS, equivalent to reductions of 65–73%. All three rates of DCD applied (7.5, 10 and 15 kg ha⁻¹) were effective in reducing N₂O emissions. In the Templeton soil, total N₂O emissions were reduced from 37.4 kg N₂O-N ha⁻¹ without DCD to 14.6–16.3 kg N₂O-N ha⁻¹ when DCD was applied either immediately or 10 days after the urine application. These reductions are similar to those in an earlier study where DCD was applied as a solution. Therefore, treating grazed pasture soils with an FPS of DCD is an effective technology to mitigate N₂O emissions from cow urine patch areas in grazed pasture soils.     

Nitrous oxide emissions from grassland and spring barley, following N fertiliser application with and without nitrification inhibitors

The aims of this study were to assess the effectiveness of the nitrification inhibitors dicyandiamide (DCD) and nitrapyrin on reducing emissions of nitrous oxide (N₂O) following application of NH₄ ⁺ or NH₄ ⁺-forming fertilisers to grassland and spring barley. DCD was applied to grassland with N fertiliser applications in April and August in 1992 and 1993, inhibiting N₂O emissions by varying amounts depending on the fertiliser form and the time of application. Over periods of up to 2 months following each application of DCD, emissions of N₂O were reduced by 58–78% when applied with urea (U) and 41–65% when applied with ammonium sulphate (AS). Annual emissions (April to March) of N₂O were reduced by up to 58% and 56% in 1992–1993 and 1993–1994, respectively. Applying DCD to ammonium nitrate (AN) fertilised grassland did not reduce emissions after the April 1993 fertilisation, but emissions following the August application were reduced. Nitrapyrin was only applied once, with the April fertiliser applications in 1992, reducing N₂O emissions over the following 12 months by up to 40% when applied with U. When N fertiliser was applied in June without DCD, the DCD applied in April was still partly effective; N₂O emissions were reduced 50%, 60% and 80% as effectively as the emissions following the April applications, for AS in 1993, U in 1992 and 1993, respectively. In 1992 the persistence of an inhibitory effect was greater for nitrapyrin than for DCD, increasing after the June fertiliser application as overall emissions from U increased. There was no apparent reduction in effectiveness following repeated applications of DCD over the 2 years. N₂O emissions from spring barley, measured only in 1993, were lower than from grassland. DCD reduced emissions from applied U by 40% but there was no reduction with AN. The results demonstrate considerable scope for reducing emissions by applying nitrification inhibitors with NH₄ ⁺ or NH₄ ⁺-forming fertilisers; this is especially so for crops such as intensively managed grass where there are several applications of fertiliser nitrogen per season, as the effect of inhibitors applied in April persists until after a second fertiliser application in June. Received: 30 August 1996     

The use of a nitrification inhibitor, dicyandiamide (DCD), to decrease nitrate leaching and nitrous oxide emissions in a simulated grazed and irrigated grassland

Abstract. In grazed dairy pasture systems, a major source of NO₃^– leached and N₂O emitted is the N returned in the urine from the grazing animal. The objective of this study was to use lysimeters to measure directly the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO₃^– leaching and N₂O emissions from urine patches in a grazed dairy pasture under irrigation. The soil was a free‐draining Lismore stony silt loam (Udic Haplustept loamy skeletal) and the pasture was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). The use of DCD decreased NO₃^–‐N leaching by 76% for the urine N applied in the autumn, and by 42% for urine N applied in the spring, giving an annual average reduction of 59%. This would reduce the NO₃^–‐N leaching loss in a grazed paddock from 118 to 46 kg N ha^–1 yr^–1. The NO₃^–‐N concentration in the drainage water would be reduced accordingly from 19.7 to 7.7 mg N L^–1, with the latter being below the drinking water guideline of 11.3 mg N L^–1. Total N₂O emissions following two urine applications were reduced from 46 kg N₂O‐N ha^–1 without DCD to 8.5 kg N₂O‐N with DCD, representing an 82% reduction. In addition to the environmental benefits, the use of DCD also increased herbage production by more than 30%, from 11 to 15 t ha^–1 yr^–1. The use of DCD therefore has the potential to make dairy farming more environmentally sustainable by reducing NO₃^– leaching and N₂O emissions.     

Nitrification Inhibitor Effects on Nitrous Oxide Emission,Nitrogen Transformation,and Maize (Zea mays L.) Yield in Loamy Sand Soil in Thailand

The nitrification inhibitors (NIs) effects on soil nitrogen (N) fates and maize yields were investigated in a loamy-sand soil in Thailand. The treatments were chemical fertilizer (CF) and CF with dicyandiamide (DCD) or neem oil at two rates of 5% and 10%. Compared to the CF plot, DCD and neem oil reduced the cumulative nitrous oxide (N₂O) emission by the equivalent of 26% and 10%, respectively (P < 0.05). DCD and neem oil had a positive effect in slowing ammonium (NH₄⁺)-conversion and prolonging NH₄⁺-N in the soil with a maximum efficiency of 45% and 30%, respectively. NO₃^–N was higher in the NI plots (P < 0.05), but the effect was less pronounced later in the growing season. Adding the NIs increased maize yields and N uptake, but was only significant (P < 0.10) for neem oil. Results indicate that applying NIs is an effective method to mitigate soil N losses and enhancing N use efficiency in a tropical, agricultural field.     

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%.     

Comparison of the effectiveness of a nitrification inhibitor, dicyandiamide, in reducing nitrous oxide emissions in four different soils under different climatic and management conditions

Nitrous oxide (N₂O) is a potent greenhouse gas and, in New Zealand, about one‐third of the total greenhouse gas emissions from the agricultural sector are of N₂O, mostly derived from animal excreta in grazed pasture soils. The aim of this study was to determine the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in reducing N₂O emissions from animal urine patches in four different soils located in different regions of New Zealand with different soil, climatic and management conditions. The four soils are Templeton fine sandy loam and Lismore stony silt loam in Canterbury in the South Island, Horotiu silt loam in the Waikato region and Taupo pumice sand near Lake Taupo, both in the North Island. Results showed that the application of a fine‐particle suspension nitrification inhibitor, DCD, to grazed pasture soils was very effective in reducing N₂O emissions in all four different soils. Total N₂O emissions (over 69–137 days) from animal urine patches ranged from 1 to 20.9 kg N₂O‐N ha^?1 without DCD. These were reduced to 0.31–5.7 kg N₂O‐N ha^?1 by the use of DCD, representing 61–73% reductions (with an average of 70% reduction). The N₂O‐N emission factor from animal urine N, EF₃, was reduced from an average of 0.9 to 0.3% by the use of DCD. These results demonstrate the potential of using nitrification inhibitors to mitigate N₂O emissions in a wide range of grazed pasture soils under different climatic and management conditions.     

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

Recent 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.     

Use of nitrogen process inhibitors for reducing gaseous nitrogen losses from land-applied farm effluents

Applications of dairy farm effluents to land may lead to ammonia (NH₃) volatilization and nitrous oxide (N₂O) emissions. Nitrogen (N) transformation process inhibitors, such as urease inhibitors (UIs) and nitrification inhibitors (NIs), have been used to reduce NH₃ and N₂O losses derived from agricultural N sources. The objective of this study was to examine the effects of amending dairy effluents with UI (N-(n-butyl) thiophosphoric triamide (NBTPT)) and NI (dicyandiamide (DCD)) on NH₃ and N₂O emissions. Treatments included either fresh or stored manure and either fresh or stored farm dairy effluent (FDE), with and without NBTPT (0.25 g kg^?1 N) or DCD (10 kg ha^?1), applied to a pasture on a free-draining volcanic parent material soil. The nutrient loading rate of FDE and manure, which had different dry matter contents (about 2 and 11 %, respectively) was 100 kg N ha^?1. Application of manure and FDE led to NH₃ volatilization (15, 1, 17 and 0.4 % of applied N in fresh manure, fresh FDE, stored manure and stored FDE, respectively). With UI (NBTPT), NH₃ volatilization from fresh manure was significantly (P?<?0.05) decreased to 8 % from 15 % of applied N, but the UI did not significantly reduce NH₃ volatilization from fresh FDE. The N₂O emission factors (amount of N₂O–N emitted as a percentage of applied N) for fresh manure, fresh FDE and stored FDE were 0.13?±?0.02, 0.14?±?0.03 and 0.03?±?0.01 %, respectively. The NI (DCD) was effective in decreasing N₂O emissions from stored FDE, fresh FDE and fresh manure by 90, 51 and 46 % (P?<?0.05), respectively. All types of effluent increased pasture production over the first 21 days after application (P?<?0.05). The addition of DCD resulted in an increase in pasture production at first harvest on day 21 (P?<?0.05). This study illustrates that UIs and NIs can be effective in mitigating NH₃ and N₂O emissions from land-applied dairy effluents.     

Effect of plantain on nitrous oxide emissions and soil nitrification rate in pasture soil under a simulated urine patch in Canterbury,New Zealand

Purpose

The aim of this research was to quantify the effect of plantain (Plantago lanceolata L.) on soil nitrification rate, functional gene abundance of soil ammonia oxidisers, and the concomitant effect on nitrous oxide emissions from urine patches in a shallow, free-draining soil in Canterbury during late autumn/winter season.

Materials and methods

Urine was collected from dairy cows grazing either ryegrass/white clover (RGWC), 30% plantain (P30) mixed in with RGWC or 100% plantain (P100) pasture, and applied at two rates (700 or 450 kg N ha^?1) to intact soil blocks growing either RGWC, P30 or P100 pasture.

Results and discussion

Results showed that increased plantain content reduced N-concentration in urine from 7.2 in RGWC urine to 4.5 and 3.7 g N L^?1 in P30 and P100 urine, respectively. Total N₂O emissions and emission factors (EF₃) from urine-treated pastures were low, <?2 kg N ha^?1 and <?0.22%, respectively. Urine application at the lower urine N-loading rate of 450 kg N ha^?1 (i.e. representative of that in a P30 urine patch) resulted in 30% lower N₂O emissions (P?<?0.01) and 35% lower soil nitrate concentrations (P?<?0.001) compared to those at the higher urine loading rate of 700 kg N ha^?1 (i.e. representative of that in a RGWC urine patch). Increasing plantain content in the pasture sward from 0 to 30% and 100% with urine N applied at the same loading rate did not reduce N₂O emissions or nitrification compared to the standard ryegrass-white clover pasture. Cow urine derived from the different pasture diets had no effect on N₂O emissions, N transformation or ammonia-oxidiser abundance in soil compared to the RGWC urine applied at the same rate.

Conclusions

The main effect of plantain in this study appears to be related to the reduction in urine N-loading rate, rather than factors related to urine properties or plantain-soil interactions.

     

Short‐term N2O,CO2, NH3 fluxes,and N/C transfers in a Danish grass‐clover pasture after simulated urine deposition in autumn

Urine patches are significant hot‐spots of C and N transformations. To investigate the effects of urine composition on C and N turnover and gaseous emissions from a Danish pasture soil, a field plot study was carried out in September 2001. Cattle urine was amended with two levels of ¹³C‐ and ¹⁵N‐labeled urea, corresponding to 5.58 and 9.54 g urea‐N l^–1, to reflect two levels of protein intake. Urine was then added to a sandy‐loam pasture soil equivalent to a rate of 23.3 or 39.8 g urea‐N m^–2. Pools and isotopic labeling of nitrous oxide (N₂O) and CO₂ emissions, extractable urea, ammonium (NH₄⁺), and nitrate (NO₃^–), and plant uptake were monitored during a 14 d period, while ammonia (NH₃) losses were estimated in separate plots amended with unlabeled urine. Ammonia volatilization was estimated to account for 14% and 12% of the urea‐N applied in the low (UL) and high (UH) urea treatment, respectively. The recovery of urea‐derived N as NH₄⁺ increased during the first several days, but isotopic dilution was significant, possibly as a result of stress‐induced microbial metabolism. After a 2 d lag phase, nitrification proceeded at similar rates in UL and UH despite a significant difference in NH₄⁺ availability. Nitrous oxide fluxes were low, but generally increased during the 14 d period, as did the proportion derived from urea‐N. On day 14, the contribution from urea was 23% (UL) and 13% (UH treatment), respectively. Cumulative total losses of N₂O during the 14 d period corresponded to 0.021% (UL) and 0.015% (UH) of applied urea‐N. Nitrification was probably the source of N₂O. Emission of urea‐derived C as CO₂ was only detectable within the first 24 h. Urea‐derived C and N in above‐ground plant material was only significant at the first sampling, indicating that uptake of urine‐C and N via the leaves was small. Urine composition did not influence the potential for N₂O emissions from urine patches under the experimental conditions, but the importance of site conditions and season should be investigated further.     

Cassava (Manihot Esculenta Crantz) Yields,Soil Nitrous Oxide Emission,and Soil Nitrogen Transformation Affected by Nitrification Inhibitors in Loamy Sand Soil in Thailand

The effects of nitrification inhibitors (NIs) on soil nitrous oxide (N₂O) emission, soil ammonium (NH₄⁺) and nitrate (NO₃^?), and cassava (Manihot esculenta Crantz) yields were investigated in a loamy sand soil in eastern Thailand. Treatments were chemical fertilizer (CF) and CF plus dicyandiamide (DCD) or neem (Azadirachta indica) oil at two rates of 5% and 10%. DCD had a greater reduction of soil N₂O flux than the neem oil (P<0.10). DCD and neem oil retained NH₄⁺-N in the soil by 79% and 63% (P ≤ 0.10), respectively. The NI effect on soil NO₃^?-N was small due to a low N fertilizer rate. The cassava root yield and N uptake were increased 4–11% and 2–18%, respectively, by use of NIs, but they were only significant for DCD (P ≤ 0.10). These findings suggest that NIs application may be a promising method for minimizing nitrogen loss and enhancing crop yields in a tropical cassava field.     

Alternatives to regular urea for abating N losses in lettuce production under sub-tropical climate

Alternative fertilization practices are needed for reducing gaseous and leaching N losses at high urea application rates. The objective of this study was to compare gaseous N emissions (N₂O and NH₃) and NO₃ ^? concentrations in the soil solution during two successive lettuce cropping seasons under contrasting fertilization practices. Treatments were fertilization with regular urea (U), urea treated with urease [N-(n-butyl) thiophosphoric triamide (NBPT)] and nitrification [dicyandiamide (DCD)] inhibitors (UIs), non-acidified pig slurry compost (PSC), acidified pig slurry compost (APSC), and an unfertilized control (C). Acidification of pig slurry during composting had no impact on soil cumulative N₂O emissions during the cropping seasons. The use of composts resulted in emission factors (EFs) (PSC, 0.09% of applied N; APSC, 0.16%) an order of magnitude smaller than with regular urea (1.63%). Similarly, adding NBPT and DCD to urea reduced the N₂O EF from 1.63 to 0.37% of applied N and fertilizer-induced NH₃ emissions from 30.2 to 3.4% of applied N. Composts and UI resulted in yield-scaled N₂O emissions that were 33 to 49% lower than the unfertilized control and 64 to 73% lower than the regular urea estimates, indicating a greater efficiency of supplied N with composts and UI. Nitrate concentration of the soil solution (at 0.1 and 0.3 m) in PSC, APSC, and UI plots was similar to the control and up to 17 times lower than with regular urea, indicating reduced risks for leaching losses. We conclude that, as compared to regular urea, the use of composted pig slurry, with and without acidification, and the addition of NBPT and DCD inhibitors to urea are good practices to reduce environmental N losses from lettuce production under sub-tropical climate.     

Tillage effects on N2O emissions as influenced by a winter cover crop

Conservation tillage practices are widely used to protect against soil erosion and soil C losses, whereas winter cover crops are used mainly to protect against N losses during autumn and winter. For the greenhouse gas balance of a cropping system the effect of reduced tillage and cover crops on N₂O emissions may be more important than the effect on soil C. This study monitored emissions of N₂O between September 2008 and May 2009 in three tillage treatments, i.e., conventional tillage (CT), reduced tillage (RT) and direct drilling (DD), all with (+CC) or without (−CC) fodder radish as a winter cover crop. Cover crop growth, soil mineral N dynamics, and other soil characteristics were recorded. Furthermore, soil concentrations of N₂O were determined eight times during the monitoring period using permanently installed needles. There was little evidence for effects of the cover crop on soil mineral N. Following spring tillage and slurry application soil mineral N was dominated by the input from slurry. Nitrous oxide emissions during autumn, winter and early spring remained low, although higher emissions from +CC treatments were indicated after freezing events. Following spring tillage and slurry application by direct injection N₂O emissions were stimulated in all tillage treatments, reaching 250-400 μg N m⁻² h⁻¹ except in the CT + CC treatment, where emissions peaked at 900 μg N m⁻² h⁻¹. Accumulated emissions ranged from 1.6 to 3.9 kg N₂O ha⁻¹. A strong positive interaction between cover crop and tillage was observed. Soil concentration profiles of N₂O showed a significant accumulation of N₂O in CT relative to RT and DD treatments after spring tillage and slurry application, and a positive interaction between slurry and cover crop residues. A comparison in early May of N₂O emissions with flux estimates based on soil concentration profiles indicated that much of the N₂O emitted was produced near the soil surface.     

Effect of application rate of a nitrification inhibitor,dicyandiamide (DCD), on nitrification rate,and ammonia-oxidizing bacteria and archaea growth in a grazed pasture soil: An incubation study

Purpose

Dicyandiamide (DCD) has been used commercially in New Zealand to reduce nitrate leaching and N₂O emissions in grazed pastures. However, there is a lack of information in the literature on the optimum rate of DCD to achieve the environmental benefits while at the same time reducing the cost of the technology. The objective of this study was to determine the effect of DCD application rate on its effectiveness to inhibit ammonia oxidizer growth and nitrification rate in a grazed pasture soil.

Materials and methods

The soil was a Templeton silt loam (Immature Pallic Soil; Udic Haplustepts) collected from Lincoln University Research Dairy Farm with a mixed pasture consisting of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) and was incubated alone (control) or with cow urine at 700 kg N/ha with 6 rates of DCD [0, 2.5, 5, 7.5, 10 (applied twice), 15 and 20 kg/ha] in incubation vessels. The incubation vessels were placed randomly in an incubator with a constant temperature of 12 °C. During 112 days of incubation, soil subsamples were taken at different time intervals to measure the concentrations of NO₃ ^?-N and NH₄ ⁺-N and the amoA gene copy numbers of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA).

Results and discussion

DCD applied at all the different rates inhibited nitrification in urine-treated soils, but the effectiveness increased with DCD application rate. In addition, AOB growth and the amounts of nitrate-N in the soil were significantly related to the application rate of DCD. However, AOA population abundance showed no relationship to the application rate of DCD. The DCD rate at which the AOB growth rate and nitrate-N concentration were halved (effective dosage that causes 50 % reduction in nitrification rate, or ED₅₀) was about 10 kg DCD/ha.

Conclusions

These results suggest that DCD applied at relatively low rates still slowed down the nitrification rate, and the current recommended rate of 10 kg DCD/ha for DCD use in New Zealand grazed pastures would result in a 50 % reduction in nitrification rate in this soil. The actual rate of DCD application used would depend on the cost of the product and the environmental and agronomic benefits that would result from its use.     

Fluxes of nitrous oxide and nitric oxide from experimental excreta patches in boreal agricultural soil

Nitric oxide (NO) and nitrous oxide (N₂O) emissions were measured from experimental dung and urine patches placed on boreal pasture soil during two growing seasons and one autumn period until soil freezing. N₂O emissions in situ were studied by a static chamber method. NO was measured with a dynamic chamber method using a NO analyser in situ. Mean emissions from the control plots were 47.6±4.5 μg N₂ON m⁻² h⁻¹ and 12.6±1.6 μg NON m⁻² h⁻¹. N₂O and NO emissions from urine plots (132±21.2 μg N₂ON m⁻² h⁻¹ and 51.9±7.6 μg NON m⁻² h⁻¹) were higher than those from dung plots (110.0±20.1 μg N₂ON m⁻² h⁻¹ and 14.7±2.1 μg NON m⁻² h⁻¹). There was a large temporal variation in N₂O and NO emissions. Maximum N₂O emissions were measured a few weeks after dung or urine application, whereas the maximum NO emissions were detected the following year. NO was responsible on average 14% (autumn) and 34% (summer) of total (NO+N₂O)N emissions from the pasture soil. NO emissions increased with increasing soil temperature and with decreasing soil moisture. N₂O emissions increased with increasing soil moisture, but did not correlate with soil temperature. Therefore we propose that N₂O and NO were produced mainly during different microbial processes, i.e., nitrification and denitrification, respectively. The results show that the overall conditions and mechanism especially for emissions of NO are still poorly understood but that there are differences in the mechanisms regulating N₂O and NO production.     

The effect of soil pH and dicyandiamide (DCD) on N2O emissions and ammonia oxidiser abundance in a stimulated grazed pasture soil

Purpose

Nitrous oxide (N₂O) is a potent greenhouse gas which is mainly produced from agricultural soils through the processes of nitrification and denitrification. Although denitrification is usually the major process responsible for N₂O emissions, N₂O production from nitrification can increase under some soil conditions. Soil pH can affect N₂O emissions by altering N transformations and microbial communities. Bacterial (AOB) and archaeal (AOA) ammonia oxidisers are important for N₂O production as they carry out the rate-limiting step of the nitrification process.

Material and methods

A field study was conducted to investigate the effect of soil pH changes on N₂O emissions, AOB and AOA community abundance, and the efficacy of a nitrification inhibitor, dicyandiamide (DCD), at reducing N₂O emissions from animal urine applied to soil. The effect of three pH treatments, namely alkaline treatment (CaO/NaOH), acid treatment (HCl) and native (water) and four urine and DCD treatments as control (no urine or DCD), urine-only, DCD-only and urine + DCD were assessed in terms of their effect on N₂O emissions and ammonia oxidiser community growth.

Results and discussion

Results showed that total N₂O emissions were increased when the soil was acidified by the acid treatment. This was probably due to incomplete denitrification caused by the inhibition of the assembly of the N₂O reductase enzyme under acidic conditions. AOB population abundance increased when the pH was increased in the alkaline treatment, particularly when animal urine was applied. In contrast, AOA grew in the acid treatment, once the initial inhibitory effect of the urine had subsided. The addition of DCD decreased total N₂O emissions significantly in the acid treatment and decreased peak N₂O emissions in all pH treatments. DCD also inhibited AOB growth in both the alkaline and native pH treatments and inhibited AOA growth in the acid treatment.

Conclusions

These results show that N₂O emissions increase when soil pH decreases. AOB and AOA prefer different soil pH environments to grow: AOB growth is favoured in an alkaline pH and AOA growth favoured in more acidic soils. DCD was effective in inhibiting AOB and AOA when they were actively growing under the different soil pH conditions.