Heterotrophic and autotrophic nitrification in two acid pasture soils

Laboratory incubation experiments, using ¹⁵N-labeling techniques and simple analytical models, were conducted to measure heterotrophic and autotrophic nitrification rates in two acid soils (pH 4.8-5.3; 1/5 in H₂O) with high organic carbon contents (6.2-6.8% in top 5 cm soil). The soils were from pastures located near Maindample and Ruffy in the Northeast Victoria, Australia. Gross rates of N mineralization, nitrification and immobilization were measured. The gross rates of autotrophic nitrification were 0.157 and 0.119 μg N g⁻¹ h⁻¹ and heterotrophic nitrification rates were 0.036 and 0.009 μg N g⁻¹ h⁻¹ for the Maindample and Ruffy soils, respectively. Heterotrophic nitrification accounted for 19% and 7% of the total nitrification in the Maindample and Ruffy soils, respectively. The heterotrophic nitrifiers used organic N compounds and no as the substrate for nitrification.     

Effects of 3,4-dimethylpyrazole phosphate (DMPP) on the abundance of ammonia oxidizers and denitrifiers in two different intensive vegetable cultivation soils

Purpose

Nitrification and denitrification in the N cycle are affected by various ammonia oxidizers and denitrifying microbes in intensive vegetable cultivation soils, but our current understanding of the effect these microbes have on N₂O emissions is limited. The nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP), acts by slowing nitrification and is used to improve fertilizer use efficiency and reduce N losses from agricultural systems; however, its effects on nitrifier and denitrifier activities in intensive vegetable cultivation soils are unknown.

Materials and methods

In this study, we measured the impacts of DMPP on N₂O emissions, ammonia oxidizers, and denitrifying microbes in two intensive vegetable cultivation soils: one that had been cultivated for a short term (1 year) and one that had been cultivated over a longer term (29 years). The quantitative PCR technique was used in this study. Three treatments, including control (no fertilizer), urea alone, and urea with DMPP, were included for each soil. The application rates of urea and DMPP were 1800 kg ha^?1 and 0.5% of the urea-N application rate.

Results and discussion

The application of N significantly increased N₂O emissions in both soils. The abundance of ammonia-oxidizing bacteria (AOB) increased significantly with high rate of N fertilizer application in both soils. Conversely, there was no change in the growth rate of ammonia-oxidizing archaea (AOA) in response to the applied urea despite the presence of larger numbers of AOA in these soils. This suggests AOB may play a greater role than AOA in the nitrification process, and N₂O emission in intensive vegetable cultivation soils. The application of DMPP significantly reduced soil NO₃^?-N content and N₂O emission, and delayed ammonia oxidation. It greatly reduced AOB abundance, but not AOA abundance. Moreover, the presence of DMPP was correlated with a significant decrease in the abundance of nitrite reductase (nirS and nirK) genes.

Conclusions

Long-term intensive vegetable cultivation with heavy N fertilization altered AOB and nirS abundance. In vegetable cultivation soils with high N levels, DMPP can be effective in mitigating N₂O emissions by directly inhibiting both ammonia oxidizing and denitrifying microbes.

     

Effects of urease inhibitors on nitrification in soils

The effects of 10 urease inhibitors on nitrification in soils were studied by determining the effects of 10 and 50 parts/10⁶ (soil basis) of each inhibitor on the amounts of nitrate and nitrite produced when soils treated with ammonium sulfate (200 μg of ammonium N/g of soil) were incubated (30°C) under aerobic conditions for 14 days. The urease inhibitors used (catechol. hydroquinone, p-benzoquinone, 2,3-dimethyl-p-benzoquinone, 2,5-dimethyl-p-benzoquinone. 2,6-dimethyl-p-benzoquinone. 2,5-dichloro-p-benzoquinone, 2,6-dichloro-p-benzoquinone. sodium p-chloromercuribenzoate, and phenylmercuric acetate) were those found most effective in previous work to evaluate more than 130 compounds as soil urease inhibitors. Their effects on nitrification were compared with those of three compounds patented as soil nitrification inhibitors (N-Serve. AM. and ST).Most of the urease inhibitors studied had little effect on nitrification when applied at the rate of 10 μg/g of soil. but had marked inhibitory effects when applied at the rate of 50 μg/g of soil. None inhibited nitrification as effectively as N-Serve. but phenylmercuric acetate inhibited nitrification more effectively than did AM or ST when applied at the rate of 10 μg/g of soil. Phenylmercuric acetate, 2,5-dimethyl-p-benzoquinone, and 2,6-dimethyl-p-benzoquinone had very marked effects on nitrification when applied at the rate of 50 μg/g of soil.     

Effects of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on abundance and activity of ammonia oxidizers in soil

Biology and Fertility of Soils - Recent evidence from several environments suggest that besides autotrophic ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA) are also able to...     

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.     

Restricted nitrous oxide emissions by ammonia oxidizers in two agricultural soils following excessive urea fertilization

Journal of Soils and Sediments - Nitrogen (N) fertilizer placement in bands is a widely accepted agricultural practice to increase N use efficiency. An excessive ammonium concentration in a...     

Effect of urease and nitrification inhibitors on N transformation, gaseous emissions of ammonia and nitrous oxide, pasture yield and N uptake in grazed pasture system

Nitrogen (N) losses via nitrate (NO₃⁻) leaching, ammonia (NH₃) volatilization and nitrous oxide (N₂O) emissions from grazed pastures in New Zealand are one of the major contributors to environmental degradation. The use of N inhibitors (urease and nitrification inhibitors) may have a role in mitigating these N losses. A one-year field experiment was conducted on a permanent dairy-grazed pasture site at Massey University, Palmerston North, New Zealand to quantify these N losses and to assess the effect of N inhibitors in reducing such losses during May 2005-2006. Cow urine at 600 kg N ha⁻¹ rate with or without urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT) or (trade name “Agrotain”) (3 L ha⁻¹), nitrification inhibitor dicyandiamide (DCD) (7 kg ha⁻¹) and the use of double inhibitor (DI) containing a combination of both Agrotain and DCD (3:7) were applied to field plots in autumn, spring and summer. Pasture production, NH₃ and N₂O fluxes, soil mineral N concentrations, microbial biomass C and N, and soil pH were measured following the application of treatments during each season. All measured parameters, except soil microbial biomass C and N, were influenced by the added inhibitors during the three seasons. Agrotain reduced NH₃ emissions over urine alone by 29%, 93% and 31% in autumn, spring and summer respectively but had little effect on N₂O emission. DCD reduced N₂O emission over urine alone by 52%, 39% and 16% in autumn, spring and summer respectively but increased NH₃ emission by 56%, 9% and 17% over urine alone during those three seasons. The double inhibitor reduced NH₃ by 14%, 78% and 9% and N₂O emissions by 37%, 67% and 28% over urine alone in autumn, spring and summer respectively. The double inhibitor also increased pasture dry matter by 10%, 11% and 8% and N uptake by the 17%, 28% and 10% over urine alone during autumn, spring and summer respectively. Changes in soil mineral N and pH suggested a delay in urine-N hydrolysis with Agrotain, and reduced nitrification with DCD. The combination of Agrotain and DCD was more effective in reducing both NH₃ and N₂O emissions, improving pasture production, controlling urea hydrolysis and retaining N in NH₄⁺ form. These results suggest that the combination of both urease and nitrification inhibitors may have the most potential to reduce N losses if losses are associated with urine and improve pasture production in intensively grazed systems.     

Effects of form of effluent,season and urease inhibitor on ammonia volatilization from dairy farm effluent applied to pasture

Purpose

With land application of farm effluents from cows during housing or milking as an accepted practice, there are increasing concerns over its effect on nitrogen (N) loss through ammonia (NH₃) volatilization. Understanding the relative extent and seasonal variation of NH₃ volatilization from dairy effluent is important for the development of management practices for reducing NH₃ losses. The objectives of this study were to determine potential NH₃ losses from application of different types of dairy effluent (including both liquid farm dairy effluent (FDE) and semi-solid dairy farm manure) to a pasture soil during several contrasting seasons and to evaluate the potential of the urease inhibitor (UI)—N-(n-butyl) thiophosphoric triamide (NBTPT, commercially named Agrotain^®) to reduce gaseous NH₃ losses.

Material and methods

Field plot trials were conducted in New Zealand on an established grazed pasture consisting of a mixed perennial ryegrass (Lolium perenne L.)/white clover (Trifolium repens L.) sward. An enclosure method, with continuous air flow, was used to compare the effects of treatments on potential NH₃ volatilization losses from plots on a free-draining volcanic parent material soil which received either 0 (control) or 100 kg N ha^?1 as FDE or manure (about 2 and 15 % of dry matter (DM) contents in FDE or manure, respectively) with or without NBTPT (0.25 g NBTPT kg^?1 effluent N). The experiment was conducted in the spring of 2012 and summer and autumn of 2013.

Results and discussion

Results showed that application of manure and FDE, both in fresh and stored forms, potentially led to NH₃ volatilization, ranging from 0.6 to 19 % of applied N. Difference in NH₃ losses depended on the season and effluent type. Higher NH₃ volatilization was observed from both fresh and stored manure, compared to fresh and stored FDE. The difference was mainly due to solid contents. The losses of NH₃ were closely related to NH₄ ⁺-N content in the two types of manure. However, there was no relationship between NH₃ losses and NH₄ ⁺-N content in either type of FDE. There was no consistent seasonal pattern, although lower NH₃ losses from fresh FDE and stored FDE applied in spring compared to summer were observed. Potential NH₃ losses from application of fresh FDE or manure were significantly (P?<?0.05) reduced by 27 to 58 % when NBTPT was added, but the UI did not significantly reduce potential NH₃ volatilization from stored FDE or manure.

Conclusions

This study demonstrated that NH₃ losses from application of FDE were lower than from manure and that UIs can be effective in mitigating NH₃ emissions from land application of fresh FDE and manure. Additionally, reducing the application of FDE in summer can also potentially reduce NH₃ volatilization from pasture soil.     

棕壤线虫对尿素配施尿酶抑制剂和硝化抑制剂的响应研究

Effects of urea amended with urease and nitrification inhibitors on soil nematode communities were studied in a Hapli- Udic Argosol （Cambisol, FAO） in Liaoning Province of Northeast China. A completely random design with four treatments, i.e., conventional urea （CU）, slow-release urea amended with a liquid urease inhibitor （SRU1）, SRU1 ＋nitrification inhibitor dicyandiamide （SRU2）, and SRU1 ＋ nitrification inhibitor 3,5-dimethylpyrazole （SRU3） and four replicates were applied. Thirty-nine genera of nematodes were identified, with Cephalobus and Aphelenchus being dominant; and in all treatments, the dominant trophic group was bacterivores. In addition, during the growth period of spring wheat （Triticum aestivum L.）, soil urease activity was lower in SRUs than in CU. The numbers of total nematodes and bacterivores at wheat heading and ripening stages, and omnivores-predators at ripening stage were higher in SUR3 than in CU, SRU1 and SRU2 （P 〈 0.05）.     

Biochar addition affected the dynamics of ammonia oxidizers and nitrification in microcosms of a coastal alkaline soil

Biochar amendments have frequently been reported to alter microbial communities and biogeochemical processes in soils. However, the impact of biochar application on bacterial (AOB) and archaeal ammonia oxidizers (AOA) remains poorly understood. In this study, we investigated the responses of AOB and AOA to the application of biochar derived from cotton stalk at rates of 5, 10, and 20 % by weight to a coastal alkaline soil during a 12-week incubation. The results showed that the amoA gene of AOB consistently outnumbered that of AOA, whereas only the AOA amoA gene copy number was significantly correlated with the potential ammonia oxidation (PAO) rate (P?<?0.01). The significant decrease of PAO rates in biochar treatments occurred after incubation for 4–6 weeks, which were distinctly longer than that in the control (2 weeks). The PAO rates were significantly different among treatments during the first 4 weeks of incubation (P?<?0.05), with the highest usually in the 10 % treatment. Biochar application significantly increased the abundance of both nitrifiers in the 4 weeks of incubation (P?<?0.05). Biochar amendment also decreased AOA diversity, but increased AOB diversity, which resulted in different community structures of both nitrifiers (P?<?0.01), as shown by the differences between the 5 % biochar and the control treatments. We conclude that biochar application generally enhanced the abundance and altered the composition of ammonia oxidizers; the rate of biochar application also affected the rate and dynamics of nitrification, and the risk for increasing the alkalinity and N leaching of the studied soil was lower with a lower application rate.     

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%.     

Humic acids buffer the effects of urea on soil ammonia oxidizers and potential nitrification

Humic acids (HAs) play an important role in the global nitrogen cycle by influencing the distribution, bioavailability, and ultimate fate of organic nitrogen. Ammonium oxidation by autotrophic ammonia-oxidizing bacteria (AOB) is a key process in ecosystems and is limited, in part, by the availability of NH₄⁺. We evaluated the impact of HAs on soil AOB in microcosms by applying urea (1.0%, equal to 10 mg urea/g soil) with 0.1% bHA (biodegraded lignite humic acids, equal to 1 mg/g soil), 0.1% cHA (crude lignite humic acids) or no amendment. AOB population size, ammonium and nitrate concentrations were monitored for 12 weeks after urea and HA application. AOB densities (quantified by real-time PCR targeting the amoA) in the Urea treatments increased about ten-fold (the final abundance: 5.02 × 10⁷ copies (g of dry soil)⁻¹) after one week of incubation and decreased to the initial density after 12 weeks incubation; the population size of total bacteria (quantified by real-time PCR with a universal bacterial probe) decreased from 1.12 × 10¹⁰ to 2.59 × 10⁹ copies (g of dry soil)⁻¹ at week one and fluctuated back to the initial copy number at week 12. In the Urea + bHA and Urea + cHA treatments, the AOB densities were 4 and 6 times higher, respectively, than the initial density of approximately 5.07 × 10⁶ copies (g of dry soil)⁻¹ at week 1 and did not change much up to week 4; the total bacteria density changed little over time. The AOB and total bacteria density of the controls changed little during the 12 weeks of incubation. The microbial community composition of the Urea treatment, based on T-RFLP using CCA (canonical correspondence analysis) and pCCA (partial CCA) analysis, was clearly different from those of other treatments, and suggested that lignite HAs buffered the change in diversity and quantity of total bacteria caused by the application of urea to the soil. We hypothesize that HAs can inhibit the change in microbial community composition and numbers, as well as AOB population size by reducing the hydrolysis rate from urea to ammonium in soils amended with urea.     

脲酶抑制剂与硝化抑制剂对稻田氨挥发的影响

采用密闭室间歇通气法和15N标记技术研究了尿素施入稻田后氨挥发损失特征以及脲酶抑制剂(N-丁基硫代磷酰三胺,NBPT)和硝化抑制剂(3, 4-二甲基吡唑磷酸盐,DMPP)对稻田氨挥发损失的影响。结果表明,稻田施用尿素后第4天氨挥发速率达到峰值,氨挥发损失主要发生在施肥后21天内。与单施尿素处理相比,添加NBPT处理的氨挥发速率峰值降低27.04%,累积氨挥发损失量降低21.65%;NBPT与DMPP配施时,氨挥发速率峰值降低12.95%,累积氨挥发损失量降低13.58%;而添加DMPP时,氨挥发速率峰值增加23.61%,累积氨挥发损失量与单施尿素的差异不显著。相关性分析表明,地表水中铵态氮浓度和pH值与氨挥发速率均达极显著正相关,说明二者是影响氨挥发速率的主要因素,而气温、 地温和水温与氨挥发速率的相关性不显著。与单施尿素相比,添加脲酶抑制剂可显著增加稻谷产量。脲酶抑制剂与硝化抑制剂配合施用可更有效地提高氮肥的回收率。综合降低氨挥发、 提高水稻产量及地上部氮肥回收率的效果,添加脲酶抑制剂以及脲酶抑制剂与硝化抑制剂配施的两个处理效果较为理想,硝化抑制剂不宜单独添加。     

Linkage of N2O emissions to the abundance of soil ammonia oxidizers and denitrifiers in purple soil under long-term fertilization

Abstract

Microbial nitrification and denitrification are responsible for the majority of soil nitrous (N₂O) emissions. In this study, N₂O emissions were measured and the abundance of ammonium oxidizers and denitrifiers were quantified in purple soil in a long-term fertilization experiment to explore their relationships. The average N₂O fluxes and abundance of the amoAgene in ammonia-oxidizing bacteria during the observed dry season were highest when treated with mixed nitrogen, phosphorus and potassium fertilizer (NPK) and a single N treatment (N) using NH₄HCO₃as the sole N source; lower values were obtained using organic manure with pig slurry and added NPK at a ratio of 40%:60% (OMNPK),organic manure with pig slurry (OM) and returning crop straw residue plus synthetic NH₄HCO₃fertilizer at a ratio of 15%:85% (SRNPK). The lowest N₂O fluxes were observed in the treatment that used crop straw residue(SR) and in the control with no fertilizer (CK). Soil NH₄⁺provides the substrate for nitrification generating N₂O as a byproduct. The N₂O flux was significantly correlated with the abundance of the amoA gene in ammonia-oxidizing bacteria (r = 0.984, p < 0.001), which was the main driver of nitrification. During the wet season, soil nitrate (NO₃^?) and soil organic matter (SOC) were found positively correlated with N₂O emissions (r = 0.774, p = 0.041 and r = 0.827, p = 0.015, respectively). The nirS gene showed a similar trend with N₂O fluxes. These results show the relationship between the abundance of soil microbes and N₂O emissions and suggest that N₂O emissions during the dry season were due to nitrification, whereas in wet season, denitrification might dominate N₂O emission.     

脲酶抑制剂与硝化抑制剂对稻田土壤硝化、反硝化功能菌的影响

[目的]在农业生产中,脲酶抑制剂(urease inhibitor,UI)与硝化抑制剂(nitrification inhibitor,NI)常作为氮肥增效剂来提高肥料利用率。本文研究了在我国南方红壤稻田施用脲酶抑制剂与硝化抑制剂后,土壤中氨氧化细菌(ammonia oxidizing bacteria,AOB)、氨氧化古菌(ammonia-oxidizing archaea,AOA)以及反硝化细菌的丰度以及群落结构的变化特征,旨在揭示抑制剂的作用机理及其对土壤环境的影响。[方法]试验在我国南方红壤稻田进行,共设5个处理:1)不施氮肥(CK);2)尿素(U);3)尿素+脲酶抑制剂(U+UI);4)尿素+硝化抑制剂(U+NI);5)尿素+脲酶抑制剂+硝化抑制剂(U+UI+NI),3次重复。脲酶抑制剂与硝化抑制剂分别为NBPT[N-(n-butyl)thiophosphrictriamide,N-丁基硫代磷酰三胺]和DMPP(3,4-dimethylpyrazole phosphate,3,4-二甲基吡唑磷酸盐)。通过荧光定量PCR(Real-time PCR)研究水稻分蘖期与孕穗期抑制剂对三类微生物标记基因拷贝数的影响,并分析土壤铵态氮、硝态氮与三种菌群丰度的相关性;利用变性梯度凝胶电泳(DenaturingGradient Gel Electrophoresis,DGGE)分析抑制剂对土壤AOB、AOA以及反硝化细菌群落结构的影响,并对优势菌群进行系统发育分析。[结果]1)荧光定量PCR结果表明,施用氮肥对两个时期土壤中AOB的amoA基因与反硝化细菌nirK基因的拷贝数均有显著提高,而对AOA的amoA基因始终没有明显影响;AOB与nirK反硝化细菌的丰度与两个时期的铵态氮含量、分蘖期的硝态氮含量呈极显著正相关,与孕穗期的硝态氮含量相关性不显著;DMPP仅在分蘖期显著减少了AOB的amoA基因拷贝数,表明DMPP主要通过限制AOB的生长来抑制稻田土壤硝化过程;NBPT对三类微生物的丰度无明显影响;2)DGGE图谱表明,在分蘖期与孕穗期,施用氮肥均明显增加了图谱中AOB的条带数,而对AOA却没有明显影响;氮肥明显增加了孕穗期反硝化细菌的条带数;与氮肥的影响相比,抑制剂NBPT与DMPP对AOA、AOB以及反硝化菌的群落结构影响甚微;系统发育分析结果表明,与土壤中AOB的优势菌群序列较为接近的有亚硝化单胞菌和亚硝化螺菌。[结论]在南方红壤稻田中,施入氮肥可显著提高AOB与反硝化细菌的丰度,明显影响两种菌群的群落结构,而AOA较为稳定;NBPT对三类微生物的群落结构丰度无明显影响;硝化抑制剂DMPP可抑制AOB的生长但仅表现在分蘖期,这可能是其缓解硝化反应的主要途径;这也说明二者对土壤生态环境均安全可靠。     

Seagrass (Zostera marina) promotes nitrification potential and selects specific ammonia oxidizers in coastal sediments

Journal of Soils and Sediments - Seagrasses accelerate sedimentation, release oxygen and organic matter through their roots, and compete with ammonia oxidizers for ammonia/ammonium in surface...     

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.     

Methanotroph abundance not affected by applications of animal urine and a nitrification inhibitor,dicyandiamide, in six grazed grassland soils

Purpose  

Methanotrophs are an important group of methane (CH₄)-oxidizing bacteria in the soil, which act as a major sink for the greenhouse gas, CH₄. In grazed grassland, one of the ecologically most sensitive areas is the animal urine patch soil, which is a major source of both nitrate (NO₃ ⁻) leaching and nitrous oxide (N₂O) emissions. Nitrification inhibitors, such as dicyandiamide (DCD), have been used to mitigate NO₃ ⁻ leaching and N₂O emissions in grazed pastures. However, it is not clear if the high nitrogen loading rate in the animal urine patch soil and the use of nitrification inhibitors would have an impact on the abundance of methanotrophs in grazed grassland soils. The purpose of this study was to determine the effect of animal urine and DCD on methanotroph abundance in grazed grassland soils.     

Responses of ureolytic and nitrifying microbes to urease and nitrification inhibitors in selected agricultural soils in Victoria,Australia

Journal of Soils and Sediments - Urease inhibitors (UIs) such as N-(n-butyl)thiophosphoric triamide (NBPT) and nitrification inhibitors (NIs) such as 3,4-dimethylpyrazole phosphate (DMPP) have been...