Soil N Losses by Denitrification Evaluated Using the 15N Tracer Method

Molecular nitrogen (N₂) and nitrous oxide (N₂O) generated by denitrification increase N losses in the soil–plant system. This study aimed to quantify N₂ and N₂O from potassium nitrate (K¹⁵NO₃) applied to soils with different textures and moisture contents in the absence and presence of a source of carbon (C) using the ¹⁵N tracer method. In the three soils used (sandy texture (ST), sandy clay loam texture (SCLT), and clayey texture (CT)), three moisture contents were evaluated (40%, 60%, and 80% of the water holding capacity (WHC)) with (D⁺) and without (D^?) dextrose added. The treatments received 100 mg N kg^?1 (KNO₃ with 23.24 atom% ¹⁵N). N₂ emissions occurred in all of the treatments, but N₂O emissions only occurred in the D⁺ treatment, showing increases with increasing moisture content. SCLT with 80% WHC in the D⁺ treatment exhibited the highest accumulated N emission (48.26 mg kg^?1). The ¹⁵N balance suggested trapping of the gases in the soil.     

Nitrate leaching,nitrous oxide emission and N use efficiency of aerobic rice under different N application strategy

A field study was conducted in the sub-humid tropical region of India to examine the effect of different nitrogen (N) management strategies on nitrate leaching, nitrous oxide (N₂O) emission and N use efficiency in aerobic rice. Treatments were: control (no N), 120 kg N ha^?1 applied as prilled urea (PU) in conventional method, 120 kg N ha^?1 applied as neem coated urea (NCU) in conventional method, N applied as PU on the basis of leaf colour chart (LCC) reading, N applied as NCU on the basis of LCC reading, and 120 kg N ha^?1 applied as PU and farm yard manure (FYM) in 1:1 ratio. Results showed that 3.4–16.1 kg NO₃-N ha^?1 was leached below 45 cm depth and 0.61–1.12 kg N₂O-N ha^?1 was emitted from aerobic rice during the growing season. NCU when applied conventionally reduced nitrate-nitrogen (NO₃-N) leaching and N₂O emission by 18.6% and 21.4%, respectively However when applied on the basis of LCC reading NCU reduced NO₃-N leaching by 39.8% as compared to PU applied in conventional method. NCU when applied on the basis of LCC reading synchronized N supply with demand and reduced N loss, which resulted in higher yield and N use efficiency.     

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.     

Methods for measuring N2O flux from water surface and N2O dissolved in water from agricultural land

A new chamber method and a stripping method were developed for field measurements of the rate of N₂O emission from the water surface and for determinations of dissolved N₂O in water from agricultural land.

These methods were used for the measurement of drainage canal water and flooded water of rice fields during the period of June 1982 to January 1983. The results demonstrate that aquatic systems of agricultural land may provide both source and sink for atmospheric N₂O.     

Effect of crop residue C:N ratio on N2O emissions from Gray Lowland soil in Mikasa,Hokkaido, Japan

Abstract

We studied the effect of crop residues with various C:N ratios on N₂O emissions from soil. We set up five experimental plots with four types of crop residues, onion leaf (OL), soybean stem and leaf (SSL), rice straw (RS) and wheat straw (WS), and no residue (NR) on Gray Lowland soil in Mikasa, Hokkaido, Japan. The C:N ratios of these crop residues were 11.6, 14.5, 62.3, and 110, respectively. Based on the results of a questionnaire survey of farmer practices, we determined appropriate application rates: 108, 168, 110, 141 and 0 g C m^?2 and 9.3, 11.6, 1.76, 1.28 and 0 g N m^?2, respectively. We measured N₂O, CO₂ and NO fluxes using a closed chamber method. At the same time, we measured soil temperature at a depth of 5 cm, water-filled pore space (WFPS), and the concentrations of soil NH⁺ ₄-N, NO^? ₃-N and water-soluble organic carbon (WSOC). Significant peaks of N₂O and CO₂ emissions came from OL and SSL just after application, but there were no emissions from RS, WS or NR. There was a significant relationship between N₂O and CO₂ emissions in each treatment except WS, and correlations between CO₂ flux and temperature in RS, soil NH⁺ ₄-N and N₂O flux in SSL and NR, soil NH⁺ ₄-N and CO₂ flux in SSL, and WSOC and CO₂ flux in WS. The ratio of N₂O-N/NO-N increased to approximately 100 in OL and SSL as N₂O emissions increased. Cumulative N₂O and CO₂ emissions increased as the C:N ratio decreased, but not significantly. The ratio of N₂O emission to applied N ranged from ?0.43% to 0.86%, and was significantly correlated with C:N ratio (y = ?0.59 ln [x] + 2.30, r ² = 0.99, P < 0.01). The ratio of CO₂ emissions to applied C ranged from ?5.8% to 45% and was also correlated with C:N ratio, but not significantly (r ² = 0.78, P = 0.11).     

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.     

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.     

NH3 Volatilization,N2O Emission and Microbial Biomass Turnover from 15N-Labeled Manure Under Laboratory Conditions

On irrigated agricultural soils from semi-arid and arid regions, ammonia (NH₃) volatilization and nitrous oxide (N₂O) emission can be a considerable source of N losses. This study was designed to test the capture of ¹⁵N loss as NH₃ and N₂O from previous and recent manure application using a sandy, calcareous soil from Oman amended one or two times with ¹⁵N labeled manure to elucidate microbial turnover processes under laboratory conditions. The system allowed to detect ¹⁵N enrichments in evolved N₂O-N and NH₃-N of up to 17% and 9%, respectively, and total N, K₂SO₄ extractable N and microbial N pools from previous and recent ¹⁵N labeled manure applications of up to 7%, 8%, and 15%. One time manured soil had higher cumulative N₂O-N emissions (141 µg kg^?1) than repeatedly manured soil with 43 µg kg^?1 of which only 22% derived from recent manure application indicating a priming effect.     

土壤温度对北京旱地农田N2O排放的影响

在作物生长期内,通过田间自动采样系统的测定和室内温湿模拟实验,对北京地区麦豆轮作生态系统的N2O排放进行了初步研究。结果表明:在10~30℃范围内,随着土壤表层温度的升高,麦豆轮作生态系统的N2O排放通量在不同程度上有一定的增加,但不呈明显的线性相关关系。     

玉米秸秆不同构件添加对土壤N_2O排放的影响

通过室内培养试验,研究玉米秸秆不同构件及按比例混合添加对土壤N_2O排放的影响。试验设置无枯落物土壤对照(CK)及四种枯落物添加处理:茎+土壤(CKS)、叶+土壤(CKL)、鞘+土壤(CKLS)、混合枯落物(茎∶叶∶鞘=5∶3∶2)+土壤(CKM)。结果表明:培养初期添加枯落物对土壤N_2O产生激发作用,培养6d之后趋于稳定,但各添加枯落物处理高于对照;培养结束各添加不同构件及混合枯落物土壤N_2O累积排放量都显著增加(p0.05),添加茎和混合枯落物土壤N_2O排放量显著高于添加叶和鞘枯落物(p0.05)。枯落物混合对土壤N_2O排放的影响在培养前期(10~28d)有一定的促进作用,培养后期不同枯落物之间无相互作用。培养结束后各枯落物全氮含量显著高于初始值,C/N显著低于初始值(p0.05)。枯落物混合培养结束后剩余质量实测值低于预测值,全氮含量实测值高于预测值,枯落物碳氮比实测值低于预测值,土壤N_2O累积排放量差异不显著,表明枯落物混合有利于枯落物分解和氮累积,但是对N_2O累积排放影响不大。     

保护性耕作条件下小麦田N2O排放及影响因素研究

采用静态箱—气相色谱法对保护性耕作和常规耕作小麦田的N_2O排放进行了原位测量,测量了土壤温度、水分、无机氮等相关影响因子。结果表明:(1)保护性耕作及常规耕作麦田N_2O的排放具有明显的季节性变化规律,各处理变化趋势较为一致。(2)N_2O的平均排放通量和季节排放量,除免耕秸秆还田外,保护性耕作与常规耕作差异显著。(3)在小麦生长季内,保护性耕作农田均表现为N_2O的排放源。(4)各处理N_2O季节排放量大小顺序为:耙耕秸秆还田(1.64 kg/hm~2)>旋耕秸秆还田(1.59 kg/hm~2)>常规耕作秸秆还田(1.48 kg/hm~2)>深松秸秆还田(1.42 kg/hm~2)>常规耕作无秸秆还田(1.34 kg/hm~2)>免耕秸秆还田(1.33 kg/hm~2),即,与常规耕作相比,保护性耕作(除免还)N_2O排放量增加。(5)温度是制约N_2O排放的关键因素,随着温度的升高N_2O表现出增加的趋势。(6)N_2O排放与水分、土壤无机氮含量无相关性。     

日本氮素的循环和流向以及减少N2O散发和NO3-污染的对策

To feed an increasing population, large amounts of chemical nitrogen fertilizer have been used to produce much of our food, feed and fiber thereby increasing nitrogen levels in soils, natural waters, crop residues, livestock wastes, and municipal and agricultural wastes, with national and international concern about its potential adverse effects on environmental quality and public health. To understand these phenomena and problems, first the nitrogen cycle and the environment are described. Then recent trends for nitrogen cycling through the food and feed system, N₂O emissions from fertilized upland and paddy soils, and NO₃^- pollution in ground water in Japan are reported. Finally, mitigation strategies in Japan for reducing N₂O emission and NO₃^- pollution are proposed, including nitrification inhibitors, controlled release fertilizers, utilization of plant species that could suppress nitrification, utilizing the toposequence, government policy, and appropriate agricultural practices. Of all the technologies presented, use of nitrification inhibitors and controlled release fertilizers are deemed the most important with further development of these aspects of technologies being expected. These practices, if employed worldwide, could help reduce the load, or environmental deterioration, on the Earth''s biosphere.     

等氮量下不同分施次数对燥红壤N2O排放的影响

通过室内培养试验研究等氮量下不同施肥次数对N_2O排放的影响。试验设一次性施氮(S1,将200 mg/kg氮肥一次性施入土壤),二次分施(S2,将200 mg/kg氮肥分两次平均施入土壤),三次分施(S3,将200 mg/kg氮肥分80、60、60 mg/kg 3次施入土壤)和空白(CK,不施肥)4个处理。培养在65%田间持水量,30℃恒温箱中进行。结果表明,氮肥施入显著促进土壤N_2O排放;等施氮量下,不同分施次数使土壤pH呈显著性差异,而土壤pH的差异又影响了土壤N_2O累积排放量;分施次数越多,土壤酸化程度越强,N_2O累积排放量越少。因此,在等施氮量下,要充分考虑土壤酸化、N_2O排放、NO–3-N积累以及施肥成本等,确定合理分施次数。     

Mitigation options for N2O emission from a corn field in Kalimantan,Indonesia

Abstract

Field experiments were designed to quantify N₂O emissions from corn fields after the application of different types of nitrogen fertilizers. Plots were established in South Kalimantan, Indonesia, and given either urea (200 kg ha^?1), urea (170 kg ha^?1) + dicyandiamide ([DCD] 20 kg ha^?1) or controlled-release fertilizer LP-30 (214 kg ha^?1) prior to the plantation of corn seeds (variety BISI 2). Each fertilizer treatment was equivalent to 90 kg N ha^?1. Plots without chemical N fertilizer were also prepared as a control. The field was designed to have three replicates for each treatment with a randomized block design. Nitrous oxide fluxes were measured at 4, 8, 12, 21, 31, 41, 51, 72 and 92 days after fertilizer application (DAFA). Total N₂O emission was the highest from the urea plots, followed by the LP-30 plots. The emissions from the urea + DCD plots did not differ from those from the control plots. The N₂O emission from the urea + DCD plots was approximately one thirtieth of that from the urea treatment. However, fertilizer type had no effect on grain yield. Thus, the use of urea + DCD is considered to be the best mitigation option among the tested fertilizer applications for N₂O emission from corn fields in Kalimantan, Indonesia.     

Compared effects of long-term pig slurry applications and mineral fertilization on soil denitrification and its end products (N2O, N2)

The long-term (9 years) effect of pig slurry applications vs mineral fertilization on denitrifying activity, N₂O production and soil organic carbon (C) (extractable C, microbial biomass C and total organic C) was compared at three soil depths of adjacent plots. The denitrifying activities were measured on undisturbed soil cores and on sieved soil samples with acetylene method to estimate denitrification rates under field or potential conditions. Pig slurry applications had a moderate impact on the C pools. Total organic C was increased by +6.5% and microbial biomass C by ≥25%. The potential denitrifying activity on soil suspension was stimulated (×1.8, P<0.05) 12 days after the last slurry application. This stimulation was still apparent, but not significant, 10 months later and, according to both methods of denitrifying activity measurement (r ²=0.916, P<0.01 on sieved soil; r ²=0.845, P<0.001 on soil cores), was associated with an increase in microbial biomass C above a threshold of about 105 mg kg⁻¹. The effect of pig slurry on denitrification and N₂O reduction rates was detected on the surface layer (0–20 cm) only. However, no pig slurry effect could be detected on soil cores at field conditions or after NO₃ ⁻ enrichments at 20°C. Although the potential denitrifying activity in sieved soil samples was stimulated, the N₂O production was lower (P<0.03) in the plot fertilized with pig slurry, indicating a lower N₂O/(N₂O + N₂) ratio of the released gases. The pig-slurry-fertilized plot also showed a higher N₂O reduction activity, which is coherent with the lower N₂O production in anaerobiosis.     

施氮对春玉米氮素利用及农田氮素平衡的影响

田间试验研究了玉米对不同土壤氮素供应水平下作物氮素吸收利用、土壤氮素供应以及农田氮素平衡的影响。结果表明,玉米产量随施氮量的增加而显著提高,当施氮量高于N 240 kg/hm2时,产量有减少趋势;氮素当季利用率随施氮量的增加逐渐降低。土壤中硝态氮含量在玉米整个生育时期呈现先迅速下降后缓慢升高的趋势;玉米成熟期,施氮处理的各层土壤中硝态氮含量显著高于不施氮处理,各层硝态氮含量基本随施氮量的增加而升高。适量施氮促进玉米对氮素的吸收和利用,进而提高玉米生物量和产量;过量施氮导致硝态氮在土壤中大量累积,提高了硝态氮淋溶风险。施氮处理显著提高了收获后土壤中残留无机氮(Nmin),土壤残留Nmin随施氮量的增加而增加;当施氮量高于N 240 kg/hm2时,残留Nmin有下降趋势。氮素表观损失随施氮量的增加而增加。在本试验条件下,综合产量、氮肥利用率和土壤硝态氮累积情况考虑,合理施氮量应控制在N 1802~40 kg/hm2左右。     

The effect of mixing organic biological waste materials and high-N crop residues on the short-time N2O emission from horticultural soil in model experiments

Manipulating the N release from high-N crop residues by simultaneous mixing of these residues with organic biological waste (OBW) materials seems to be a possible method to reduce NO₃^– leaching. The aim of this study was to examine whether the incorporation of OBW materials together with a high-N crop residue (celery) had also an effect on N₂O emission from horticultural soil under short-term and optimised laboratory conditions. A sandy loam soil and celery residues were mixed with different OBW materials and brought into PVC tubes at 80% water-filled pore space and 15°C. Every 2.5 h, a gas sample was taken and analysed by gas chromatography for its N₂O concentration. The soil amended with only celery residues had a cumulative N₂O emission of 9.6 mg N kg^–1 soil in 50 h. When the celery residues were mixed with an OBW material, the N₂O emission was each time lower than the emission from the celery-only treatment (between 3.8 and 5.9 mg N kg^–1 soil during maximum 77 h), except with paper sludge (17.2 mg N kg^–1 soil in 100 h). The higher N₂O emission from the paper sludge treatment was probably due to its unusually low C:N ratio. Straw, green waste compost 1 (GWC1) and 2 (GWC2), saw dust, and tannic acid reduced the N₂O emission of the celery treatment by 40 to 60%. Although the N₂O reduction potential can be expected to be lower and with differing dynamics under field conditions, this study indicates that apart from reducing NO₃^– leaching, OBW application may at the same time reduce N₂O emissions after incorporation of high-N crop residues.     

Fungal N2O production in an arable peat soil in Central Kalimantan,Indonesia

Abstract

To clarify the microbiological factors that explain high N₂O emission in an arable peat soil in Central Kalimantan, Indonesia, a substrate-induced respiration-inhibition experiment was conducted for N₂O production. The N₂O emission rate decreased by 31% with the addition of streptomycin, whereas it decreased by 81% with the addition of cycloheximide, compared with a non-antibiotic-added control. This result revealed a greater contribution of the fungal community than bacterial community to the production of N₂O in the soil. The population density of fungi in the soil, determined using the dilution plate method, was 5.5 log c.f.u. g^?1 soil and 4.9 log c.f.u. g^?1 soil in the non-selective medium (rose bengal) and the selective medium for Fusarium, respectively. The N₂O-producing potential was randomly examined in each of these isolates by inoculation onto Czapek agar medium (pH 4.3) and incubation at 28°C for 14 days. Significant N₂O-producing potential was found in six out of 19 strains and in five out of seven strains isolated from the non-selective and selective media, respectively. Twenty-three out of 26 strains produced more than 20% CO₂ during the 14-day incubation period, suggesting the presence of facultative fungi in the soil. These strains were identified to be Fusarium oxysporum and Neocosmospora vasinfecta based on the sequence of 18S rDNA, irrespective of the N₂O-producing potential and the growth potential in conditions of low O₂ concentration.     

氮肥施用对西南地区紫色土冬小麦N_2O释放和反硝化作用的影响

N2O是重要的温室气体之一,由此引起的全球变暖和臭氧层破坏是当今重要的环境问题。采用遮光密闭箱和气相色谱法研究了氮肥施用对小麦地N2O释放和反硝化作用的影响。结果表明,小麦生长季节里,高氮、中氮以及不施氮处理N2O平均排放通量分别为2.71、2.42、1.97 gN.hm-.2d-1;尿素、硫酸铵、硝酸钾3种氮肥品种处理下,平均N2O排放通量分别为2.42、2.14、3.13 gN.hm-2.d-1。小麦生长季节里,高氮、中氮以及不施氮处理平均反硝化速率分别为4.91、4.50、1.67 gN.hm-.2d-1;尿素、硫酸铵、硝酸钾3种氮肥品种处理下,平均反硝化速率分别为4.50、3.68、5.29 gN.hm-.2d-1。氮肥施用明显促进了土壤-植物系统中N2O排放通量和反硝化作用,氮肥施用量水平和N2O排放通量、反硝化作用呈正相关。硝酸钾对N2O排放通量和反硝化作用贡献最大,硫酸铵最小。研究还表明,小麦地N2O释放和反硝化作用与季节有一定相关性,温度较高季节排放量及反硝化作用明显,反之则较弱。     

Nitrate leaching in soil: Tracing the NO3 sources with the help of stable N and O isotopes

Legumes increase the plant-available N pool in soil, but might also increase NO₃⁻ leaching to groundwater. To minimize NO₃⁻ leaching, N-release processes and the contribution of legumes to NO₃⁻ concentrations in soil must be known. Our objectives were (1) to quantify NO₃⁻-N export to >0.3 m soil depth from three legume monocultures (Medicago x varia Martyn, Onobrychis viciifolia Scop., Lathyrus pratensis L.) and from three bare ground plots. Furthermore, we (2) tested if it is possible to apply a mixing model for NO₃⁻ in soil solution based on its dual isotope signals, and (3) estimated the contribution of legume mineralization to NO₃⁻ concentrations in soil solution under field conditions. We collected rainfall and soil solution at 0.3 m soil depth during 1 year, and determined NO₃⁻ concentrations and δ¹⁵N and δ¹⁸O of NO₃⁻ for >11.5 mg NO₃⁻-N l⁻¹. We incubated soil samples to assess potential N release by mineralization and determined δ¹⁵N and δ¹⁸O signals of NO₃⁻ derived from mineralization of non-leguminous and leguminous organic matter.Mean annual N export to >0.3 m soil depth was highest in bare ground plots (9.7 g NO₃⁻-N m⁻²; the SD reflects the spatial variation) followed by Medicago x varia monoculture (6.0 g NO₃⁻-N m⁻²). The O. viciifolia and L. pratensis monocultures had a much lower mean annual N export (0.5 and 0.3 g NO₃⁻-N m⁻²). The averaged NO₃⁻-N leaching during 70 days was not significantly different between field estimates and incubation for the Medicago x varia Martyn monoculture.The δ¹⁵N and δ¹⁸O values in NO₃⁻ of rainfall (δ¹⁵N: 3.3±0.8‰; δ¹⁸O: 30.8±4.7‰), mineralization of non-leguminous SOM (9.3±0.9‰; 6.7±0.8‰), and mineralization of leguminous SOM (1.5±0.6‰; 5.1±0.9‰) were markedly different. Applying a linear mixing model based on these three sources to δ¹⁵N and δ¹⁸O values in NO₃⁻ of soil solution during winter 2003, we calculated 18-41% to originate from rainfall, 38-57% from mineralization of non-leguminous SOM, and 18-40% from mineralization of leguminous SOM.Our results demonstrate that (1) even under legumes NO₃⁻-N leaching was reduced compared to bare ground, (2) the application of a three-end-member mixing model for NO₃⁻ based on its dual isotope signals produced plausible results and suggests that under particular circumstances such models can be used to estimate the contributions of different NO₃⁻ sources in soil solution, and (3) in the 2nd year after establishment of legumes, they contributed approximately one-fourth to NO₃⁻-N loss.