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1.
ABSTRACT

Legumes, including hairy vetch (Vicia villosa Roth), are widely used as green manures. They fix nitrogen (N) and provide the N to other crops when they decompose, and thus are considered alternatives for chemical N fertilizers. However, N-rich plant residues, including hairy vetch, are also sources of soil nitrous oxide (N2O) emissions, a greenhouse gas. On one hand, rice (Oryza sativa L. ssp. japonica) husk biochar is widely used as a soil conditioner in Japan and has been reported as a tool to mitigate soil N2O emissions. We conducted a soil core incubation experiment (1.5 months) to compare the N2O emissions during the decomposition of surface-applied hairy vetch (0.8 kg dried hairy vetch m?2 soil) under semi-saturated soil moisture conditions (~100% water-filled pore space (WFPS)), using two soil types, namely Andosol and Fluvisol. Throughout the incubation period, the use of biochar suppressed soil NH4+-N concentrations in Andosol, whereas the effect of biochar on NH4+-N was not clear in Fluvisol. Biochar increased the nitrate (NO3?-N) levels both in Andosol and Fluvisol, suggesting a negative influence on denitrification and/or a positive influence on nitrification. Biochar application did not influence the cumulative N2O emissions. Our study suggests that rice husk biochar is not a good option to mitigate N2O emissions during the decomposition of surface-applied hairy vetch, although this study was performed under laboratory conditions without plants. However, the trends of the inorganic-N concentration changes followed by the addition of hairy vetch and biochar were markedly different between the two soil types. Thus, factors behind the differences need to be further studied.  相似文献   

2.
水分状况与供氮水平对土壤可溶性氮素形态变化的影响   总被引：3，自引：0，他引：3  
采用通气培养试验,研究比较了两种水稻土在不同水分和供氮水平下的矿质氮(TMN)和可溶性有机氮(SON)的变化特征。结果表明,加氮处理及淹水培养均显著提高青紫泥的NH4+-N含量;除加氮处理淹水培养第7 d外,潮土NH4+-N含量并未因加氮处理或淹水培养而明显升高。无论加氮与否,控水处理显著提高两种土壤的NO3--N含量,其中潮土始见于培养第7 d,青紫泥则始于培养后21 d;加氮处理可显著提高淹水培养潮土NO3--N含量,却未能提高淹水培养青紫泥NO3--N含量。两种土壤的SON含量从开始培养即逐步升高,至培养21～35 d达高峰期,随后急剧下降并回落至基础土样的水平;SON含量高峰期,潮土SON/TSN最高达80%以上,青紫泥也达60%。综上所述,潮土不仅在控水条件下具有很强硝化作用,在淹水条件下的硝化作用也不容忽视,因此氮肥在潮土中以硝态氮的形式流失的风险比青紫泥更值得关注;在SON含量高峰期,两种土壤的可溶性有机氮的流失风险也应予以重视。  相似文献   

3.
Summary The application of NH inf4 su+ -based fertilizers to soils slowly lowers soil pH, which in turn decreases nitrification rates. Under these conditions nitrification and N mineralization may be reduced. We therefore investigated the impact of liming fertilizer-acidified soils on nitrification and N mineralization. Soil samples were collected in the spring of 1987 from a field experiment, initiated in 1980, investigating N, tillage, and residue management under continuous corn (Zea mays L.). The pH values (CaCl2) in the surface soil originally ranged from 6.0 to 6.5. After 6 years the N fertilizer and tillage treatments had reduced the soil pH to values that ranged between 3.7 and 6.2. Incubation treatments included two liming rates (unlimed or SMP-determined lime requirement), two 15N-labeled fertilizer rates (0 or 20 g N m-2), and three replicates. Field-moist soil was mixed with lime and packed by original depth into columns. Labeled-15N ammonium sulfate in solution was surface-applied and columns were leached with 1.5 pore volumes of deionized water every 7 days over a 70-day period. Nitrification occurred in all pH treatments, suggesting that a ferilizer-acidified soil must contain a low-pH tolerant nitrifier population. Liming increased soil pH values (CaCl2) from 3.7 to 6.2, and increased by 10% (1.5 g N m-2) the amount of soil-derived NO3 --N that moved through the columns. This increase was the result of enhanced movement of soil-derived NO3 --N through the columns during the first 14 days of incubation. After the initial 14-day period, the limed and unlimed treatments had similar amounts of soil N leaching through the soil columns. Lime increased the nitrification rates and stimulated the early movement of fertilizer-derived NO3 --N through the soil.  相似文献   

4.
作为一种重要的土壤调节剂,生物质炭在固碳减排,尤其在氧化亚氮(N2O)减排方面的作用日益突出。本研究通过田间定位试验,分析稻麦轮作体系新鲜和田间不同时间老化生物质炭对N2O排放的影响,旨在明确生物质炭对田间N2O排放的持续效应及其作用机理。试验共设置5个处理,分别为CK（不施氮肥和生物质炭）、N（施氮肥）、NB0y（氮肥+新鲜生物质炭）、NB2y（氮肥+2年老化生物质炭）和NB5y （氮肥+5年老化生物质炭）,动态监测稻麦轮作周期N2O排放,测定水稻和小麦收获后土壤理化性质和氮循环功能基因丰度。结果表明,生物质炭显著降低土壤N2O累积排放量32.4% ~ 54.0%,且表现为NB0y> NB2y> NB5y。与N处理相比,NB0y, NB2y 和NB5y处理显著提高土壤pH值0.6 ~ 1.2个单位、土壤有机碳（SOC）含量21.4 % ~ 58.6%、硝态氮（NO3--N）含量1.7% ~ 31.3%,对土壤pH改善能力随着生物质炭老化而下降。生物质炭处理显著提高nosZ基因丰度54.9% ~ 249.4%,土壤 (nirS+nirK)/nosZ比值随着生物质炭老化而增加。相关性分析表明,土壤N2O累积排放量与pH值呈显著负相关,与NO3--N含量和amoA-AOB（氨氧化细菌）丰度呈显著正相关。因此,新鲜和田间不同时间老化生物质炭均能显著改善土壤理化特性,降低土壤 N2O排放且新鲜生物质炭的作用效果优于老化生物质炭。土壤NO3--N 含量及(nirS+nirK)/nosZ比值的增加,是导致老化生物质炭减排N2O能力降低的主要原因。  相似文献   

5.
Abstract

Laboratory and greenhouse experiments were conducted to determine the effects of rate of nitrapyrin and soil pH on nitrification of NH4 + fertilizer in soil, and growth and chemical composition of burley tobacco (Nicotiana tabacum L. cv. ‘KY ‐14'). Such experiments were needed to develop information for increasing efficiency of N fertilizer use and to lessen the fertilizer‐induced soil acidity and salt effects on tobacco plants.

Results for laboratory and greenhouse incubations indicated that nitrification proceeeded slowly below pH 5.0 and the nitrapyrin necessary to delay nitrification increased with both increasing soil pH and length of incubation time. Generally, nitrification could be delayed 30 days by nitrapyrin rates of 0.25 or 0.5 μg g‐1 regardless of soil pH. but rates of 1 μg g‐1 nitrapyrin or higher were required for 60 days and longer incubation times, particularly at higher soil pH.

Growth and morphology of tobacco plants were either unaffected, or affected positively, by low rates of nitrapyrin (up to 2 μg g‐1). However, rates of 4 μg g‐1 and above reduced total plant dry weight, reducing sugars and contents of mineral elements. Concentrations and content of plant NO3 ‐ N and Mn were greatly decreased by application of nitrapyrin. Values for most parameters measured increased with increasing soil pH. The data show that low rates of nitrapyrin may be used to alter the ratio of NO3 ‐ to NH4 + N absorbed by tobacco and possibly improve growth and safety of tobacco.  相似文献   

6.
Optimal fertilizer nitrogen (N) rates result in economic yield levels and reduced pollution. A soil test for determining optimal fertilizer N rates for wheat has not been developed for Quebec, Canada, or many other parts of the world. Therefore, the objectives were to determine: 1) the relationship among soil nitrate (NO? 3)- N, soil ammonium (NH + 4)- N and N fertilizer on wheat yields; and 2) the soil sampling times and depths most highly correlated with yield response to soil NO? 3-N and NH + 4-N. In a three year research work, wet and dried soil samples of 0- to 30- and 30- to 60-cm depths from 20 wheat fields that received four rates of N fertilizer at seeding and postseeding (plants 15 cm tall) were analyzed for NH + 4-N and NO? 3 -N using a quick-test (N-Trak) and a standard laboratory method. Wheat yield response to N fertilizer was limited, but strong to soil NO? 3-N.  相似文献   

7.
针对蔬菜灌溉水肥渗漏问题,采用田间试验和室内分析相结合,研究了番茄膜下沟灌灌水量与土壤硝态氮的根层外渗漏关系,分析了灌水量与不同根层土壤硝态氮的淋溶和保蓄特征,结果表明:灌溉不施肥条件下灌水量与土壤硝态氮淋溶量和淋溶率、灌溉施肥条件下灌水量与土壤施入硝态氮的保蓄率和渗漏率均呈直线关系;灌溉均会引起浅根层(0—20 cm)硝态氮淋溶,灌溉施肥条件下7.5～15 mm灌水量范围硝态氮积累有一个峰值,而22.5～45 mm范围则有两个峰值;灌水量在7.5～15mm之间,灌溉不施肥条件下根层土壤硝态氮淋溶率为0,灌溉施肥条件下土壤硝态氮渗漏率为0～5.19%;灌水量在22.5～45 mm之间,灌溉不施肥土壤硝态氮淋溶率为5.38%～19.08%,灌溉施肥条件下根层土壤硝态氮渗漏率为21.91%～61.96%。日光温室番茄膜下沟灌能减少肥料淋溶与渗漏的节水灌水量为15 mm。  相似文献   

8.
Corn requires high nitrogen (N) fertilizer use, but no soil N test for fertilizer N requirement is yet available in Quebec. Objectives of this research were (1) to determine the effects of soil nitrate (NO3 ?)-N, soil ammonium (NH4 +)-N, and N fertilizer rates on corn yields and (2) to determine soil sampling times and depths most highly correlated with yields and fertilizer N response under Quebec conditions. Soil samples were taken from 0- to 30-cm and 30- to 60-cm depths at seeding and postseeding (when corn height reached 20 cm) to determine soil NH4 + and NO3 ? in 44 continuous corn sites fertilized with four rates of N in two replications using a quick test (N-Trak) and a laboratory method. The N-Trak method overestimated soil NO3 ?-N in comparison with the laboratory method. Greater coefficients of determination were observed for soil NO3 ?-N analyses at postseeding compared with seeding.  相似文献   

9.
In the tropics,frequent nitrogen(N)fertilization of grazing areas can potentially increase nitrous oxide(N2O)emissions.The application of nitrification inhibitors has been reported as an effective management practice for potentially reducing N loss from the soil-plant system and improving N use efficiency(NUE).The aim of this study was to determine the effect of the co-application of nitrapyrin(a nitrification inhibitor,NI)and urea in a tropical Andosol on the behavior of N and the emissions of N2O from autotrophic and heterotrophic nitrification.A greenhouse experiment was performed using a soil(pH 5.9,organic matter content 78 g kg-1,and N 5.6 g kg-1)sown with Cynodon nlemfuensis at 60%water-filled pore space to quantify total N2O emissions,N2O derived from fertilizer,soil ammonium(NH4+)and nitrate(NO3-),and NUE.The study included treatments that received deionized water only(control,NI).No significant differences were observed in soil NH4+content between the UR and UR+NI treatments,probably because of soil mineralization and NO3-produced by heterotrophic nitrification,which is not effectively inhibited by nitrapyrin.After 56 d,N2O emissions in UR(0.51±0.12 mg N2O-N concluded that the soil organic N mineralization and heterotrophic nitrification are the main processes of NH4+and NO3-production.Additionally,it was found that N2O emissions were partially a consequence of the direct oxidation of the soil's organic N via heterotrophic nitrification coupled to denitrification.Finally,the results suggest that nitrapyrin would likely exert significant mitigation on N2O emissions only if a substantial N surplus exists in soils with high organic matter content.  相似文献   

10.
The objective of this study was to evaluate the extent to which altering pig nutrition for environmental reasons could affect the N fertilizing value of slurry. This was assessed by studying the nitrification of NH4-N and the N use efficiency of slurries obtained from growing pigs offered feeds either with commonly applied contents of crude protein (CP) and bacterially fermentable substrates (BFS) or reduced CP levels and/or elevated BFS levels. Soil/slurry mixtures were incubated for 16 weeks at 20°C using 0.2 g total slurry N addition per kg soil. In a 15 weeks lasting pot experiment with Lolium multiflorum, N derived from the same slurries was applied at two N doses with overall either 0.4 or 0.8 g total slurry N/kg soil. In the pot experiment the effect of slurry on plant growth and N uptake was compared with a mineral N fertilizer (NH4NO3) treatment and a non-fertilized control. Slurries obtained from pigs fed at reduced CP content had lower pH, total N content and proportion of NH4-N than slurries obtained from pigs fed at higher CP. Accordingly incubation of soil/slurry mixtures using slurries obtained from low CP feeds resulted in lower NO3-N concentration in the soil. Furthermore, a lower proportion of the added NH4-N was nitrified in treatments involving slurries derived from low CP feeds. Modifying the BFS content in feeds had minor effects both on slurry characteristics and on slurry NH4-N nitrification in soil. Although reduced CP and, to a lesser extent, elevated BFS altered the N release pattern to plants, slurry N use efficiency during the four cuts following the first fertilization ranged at a similar level of 32 to 33% for all types of slurry. This apparent use was significantly lower than that of the mineral N fertilizer which amounted to 72 to 75% of the added N. Nitrogen balance showed that less than 22% of the added mineral N fertilizer was lost from the soil/plant systems while from 32 to 47% of the N added with the slurries was lost independently of the type of slurry. So overall N utilization by crop and rate of slurry N recovery did not significantly differ which indicates that the investigated modifications of pig feeding appear to have no short term negative effect on the N fertilizing value of slurries.  相似文献   

11.
This work aimed to study whether soil plant analysis development (SPAD) and its modifications (SPAD/SLA, SPAD/N) were sensitive indicators of intra-seasonal nitrogen (N) changes in the soil-root-petiole-leaf continuum in sugar beets. In a three-year, field experiment, 11 occasions of measurement per year took place. Significant intra-seasonal changes of soil [total N, nitrate (NO3)-N], root (α-amino N), petiole (NO3-N) and leaf [SPAD,%N, SLA, SPAD/N, SPAD/SLA, specific leaf nitrogen (SLN)] traits were found. SPAD readings failed to predict N status changes in soil and sugar beets. SPAD modifications (SPAD/SLA, SPAD/N) gave significant correlations with root α-amino N (r = ?0.80, P < 0.001, n = 33) and petiole NO3-N (r = ?0.53, P < 0.01, n = 33) which are considered as sugar beet N status indicators. SPAD readings adjusted for intra-seasonal, leaf ontogenetic changes as they captured by SLA improved the correlations with the indicators of sugar beet N status and especially with root α-amino N. Also, SPAD/SLA gave a significantly correlation with leaf %N (r = ?0.82, P < 0.001, n = 33).  相似文献   

12.
The earthworm Pheretima hilgendorfi, one of the most common anecic species in Japan, abounds in soils with applied rice-straw residues. The influences of the worm’s activity and/or those of rice-straw application on the soil microbial community structure were studied using a microcosm approach. Low Humic Andosol was incubated with or without earthworms in a jar for a month after the following treatments: 1) no treatment, 2) chopped rice straw top-dressed on the soil and 3) rice straw incorporated into the soil. The soil NO3–-N level increased with the earthworms’ presence even in the soil without rice straw. The soil NH4+-N level was by far the highest in the soil treated with worms and no rice straw. Amounts of total and bacterial PLFAs increased due to the earthworms’ presence when rice straw was incorporated. The proportion of unsaturated fatty acids increased in the earthworm treatment while the saturated fatty acids decreased, suggesting an increase in the Gram-negative bacterial proportion. The results of principal component analysis indicated that the rice straw and the earthworms affected the soil microbial community structure independently. Any direct influence of the PLFAs contained in the worms’ bodies and in the rice straw on the soil’s PLFA profile was thought to be small.  相似文献   

13.
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.  相似文献   

14.
有机无机肥配施对酸性菜地土壤硝化作用的影响   总被引：5，自引：0，他引：5  
通过室内培养和田间试验, 研究了有机无机肥配施对酸性菜地土硝化作用的影响。培养试验条件为60%土壤最大持水量和25 ℃。 结果表明,土壤硝化作用模式为指数方程,延滞期10天。与纯化肥处理（NPK）相比,鲜猪粪配施无机肥（FPM+NPK）和猪粪堆肥配施无机肥（CPM+NPK）均能降低土壤硝化势和氨氧化潜势,猪粪堆肥配施无机肥还能增加土壤微生物量碳、 氮。鲜猪粪配施无机肥和猪粪堆肥配施无机肥处理在硝化培养和田间试验期间N2O释放量均没有差异,但硝化培养期间鲜猪粪配施无机肥的N2O释放量显著低于纯化肥处理,田间试验期间猪粪堆肥配施无机肥的N2O释放量显著低于纯化肥处理。培养试验结束后的土壤pH值与土壤硝化势间,以及硝化培养期间N2O累积释放量与土壤硝化势间均存在显著正相关关系。本研究表明, 有机无机肥配施显著影响土壤硝化作用以及硝化培养期间和田间N2O释放。  相似文献   

15.
Ammonium salts used as fertilizers may cause soil acidification by two different processes: nitrification in soil and net release of protons from roots. Their influence on soil pH may vary depending on the distance from root surface. The aim of this study was to distinguish between these two processes. For this purpose rape seedlings were grown 10 d in a system which separated roots from soil by a fine-meshed screen. As a function of distance from the plane root layer formed on the screen, pH, titratable and exchangeable acidity and NO3- and NH4-nitrogen were determined. The soil, a luvisol from loess, was supplied with no N or (NH4)2SO4 either with or without a nitrification inhibitor (DCD). The bulk soil pH remained unaffected when no N or 400 mg NH4? N kg?1 soil plus DCD was applied but it decreased from 6.6 to 5.8 without DCD. In contrast, rhizosphere pH decreased in all cases, mainly within a distance of 1 mm from the root plane only, but with gradients extending to between 2 and 4 mm into the soil. The strongest pH decrease, from 6.6 to 4.9, occurred at the root surface of plants treated with both NH4-N and DCD where most of the mineral N remained as ammonium. In this case Al was solubilized in the rhizosphere as indicated by exchangeable acidity. Total soil acidity produced in the NH4 treatment without DCD was mainly derived from nitrification compared to root released protons. However, acidification of the rhizosphere was diminished by nitrification because nitrate ions taken up by the roots counteracted net proton release. It is concluded that nitrification inhibitors may reduce proton input from ammonium fertilizers but enhance acidification at the soil-root interface which may cause Al toxicity to plants.  相似文献   

16.
 The effects of salt type and its concentration on nitrification, N mineralization and N2O emission were examined under two levels of moisture content in Yellow soil and Andosol samples as simulated to agriculture under arid/semi-arid conditions and under heavy application of fertilizer in a glass-house, respectively. The salt mixtures were composed of chlorides (NaCl and NH4Cl) or sulphates [Na2SO4 and (NH4)2SO4] and were added at various concentrations (0, 0.1, 0.2, 0.4 and 0.6 M as in the soil solution). These salts were added to non-saline Yellow soil at different moisture contents (45 or 40 and 65% of maximum water-holding capacity; WHC) and their effects on the changes in mineral N (NH4 +-N and NO3 –-N) concentration as well as N2O emission were examined periodically during laboratory incubation. We also measured urease activities to know the effect of salts on N mineralization. Furthermore, Ca(NO3)2 solution was added at various concentrations (0, 0.1, 0.3, 0.5 and 0.8 M as in the soil solution) to a non-saline Andosol taken from the subsurface layer in a glass-house and incubated at different moisture contents (50% and 70% of WHC) to examine their effects on changes in mineral N. Nitrification was inhibited by high, but remained unaffected by low, salt concentrations. These phenomena were shown in both the model experiments. It was considered that the salinity level for inhibition of nitrification was an electric conductivity (1 : 5) of 1 dS m–1. This level was independent of the type of salts or soil, and was not affected by soil moisture content. The critical level of salts for urease activities was about 2 dS m–1. The emission rate of N2O was maximum at the beginning of the incubation period and stabilized at a low level after an initial peak. There was no significant difference in N2O emission among the treatments at different salt concentrations, while higher moisture level enhanced N2O emission remarkably. Received: 29 July 1998  相似文献   

17.
Abstract

Humic acids (HAs) obtained from four different soils by sequential extraction with pyrophosphate solutions at different pH values (i.e. at pH 3, 5, 7, 9, 11, and 13), were examined by ultraviolet and visible (UV-VIS) spectroscopy and elemental analysis. UV-VIS spectra from 230 to 700 nm were measured, and absorbance coefficients of 1% humic acid solutions at 600 nm (E 1% 600) and Δlog K were calculated. The shape of the spectra of humic acids depended on the soil types rather than on the pH values. The (E 1% 600) values were higher in the neutral region, and lower in the alkaline region, for each pH value they decreased in the following order: buried Andosol > Andosol > Histosol ≧ Cambisol. The Δlog K values for each pH value were higher in the following order: Histosol> Cambisol > buried Andosol≧Andosol. Although the linear correlation was found to be significant between the E 1% 600 and Δlog K values, the relation between these optical properties and pH values differed among the soil types. However, in the neutral region, the higher E 1% 600 values of humic acids from buried Andosol and Andosol and the lower Δlog K values of humic acids from Cambisol and Histosol suggest that the humification degree was higher in the neutral region. Data of elemental composition and atomic ratios were obtained for each humic acid. The H/C ratios in the four soils increased gradually with increasing pH values from 5 to 13, and those for each pH value were commonly higher in the following order: Cambisol> Histosol> Andosol> buried Andosol. The O/C and OIH ratios decreased with increasing pH values. The results of the H/C versus O/C diagram suggested that decarboxylated humic acids were extracted at the higher pH values. A highly significant correlation coefficient was obtained between the H/C and OIH ratios (r= ?0.891***). Results showing that the decrease of the pH values corresponded to the order of the humic acids in the correlation curve in the H/C versus O/H diagram suggest that the humic acids with a higher content of unsaturated bonds and a higher degree of oxidation were extracted at the lower pH values within the range from 5 to 13.  相似文献   

18.
Abstract

Laboratory incubations were conducted to investigate nitrous oxide (N2O) production from a subtropical arable soil (Typic Plinthodults) incubated at different soil moisture contents (SMC) and with different nitrogen sources using a 10% (v/v) acetylene (C2H2) inhibitory technique at 25°C. The production of N2O and CO2 was monitored during the incubations and changes in the contents of KCl-extractable NO? 3-N and NH+ 4-N were determined. The production of N2O increased slightly with an increase in SMC from 40% water-holding capacity (WHC) to 70% WHC, but increased dramatically at 100% WHC. After incubation the NO? 3-N content increased even at a SMC of 100% WHC. At a SMC of 100% WHC, the addition of NH+ 4-N promoted the production of N2O and CO2, whereas the addition of NO? 3-N decreased N2O production. Compared with the incubation without C2H2, the presence of C2H2 increased NH+ 4-N content, but decreased NO? 3-N content, and there was no significant difference in N2O production. These results indicate that heterotrophic nitrification contributes to N2O production in the soil.  相似文献   

19.
The contribution of nitrification to the emission of nitrous oxide (N2O) from soils may be large, but its regulation is not well understood. The soil pH appears to play a central role for controlling N2O emissions from soil, partly by affecting the N2O product ratios of both denitrification (N2O/(N2+N2O)) and nitrification (N2O/(NO2−+NO3−). Mechanisms responsible for apparently high N2O product ratios of nitrification in acid soils are uncertain. We have investigated the pH regulation of the N2O product ratio of nitrification in a series of experiments with slurries of soils from long-term liming experiments, spanning a pH range from 4.1 to 7.8. 15N labelled nitrate (NO3−) was added to assess nitrification rates by pool dilution and to distinguish between N2O from NO3− reduction and NH3 oxidation. Sterilized soil slurries were used to determine the rates of chemodenitrification (i.e. the production of nitric oxide (NO) and N2O from the chemical decomposition of nitrite (NO2−)) as a function of NO2− concentrations. Additions of NO2− to aerobic soil slurries (with 15N labelled NO3− added) were used to assess its potential for inducing denitrification at aerobic conditions. For soils with pH?5, we found that the N2O product ratios for nitrification were low (0.2-0.9‰) and comparable to values found in pure cultures of ammonia-oxidizing bacteria. In mineral soils we found only a minor increase in the N2O product ratio with increasing soil pH, but the effect was so weak that it justifies a constant N2O product ratio of nitrification for N2O emission models. For the soils with pH 4.1 and 4.2, the apparent N2O product ratio of nitrification was 2 orders of magnitude higher than above pH 5 (76‰ and 14‰). This could partly be accounted for by the rates of chemodenitrification of NO2−. We further found convincing evidence for NO2−-induction of aerobic denitrification in acid soils. The study underlines the role of NO2−, both for regulating denitrification and for the apparent nitrifier-derived N2O emission.  相似文献   

20.
 Nitrification inhibition of soil and applied fertilizer N is desirable as the accumulation of nitrates in soils in excess of plant needs leads to enhanced N losses and reduced fertilizer N-use efficiency. In a growth chamber experiment, we studied the effects of two commercial nitrification inhibitors (NIs), 4-amino 1,2,4-triazole (ATC) and dicyandiamide (DCD), and a commonly available and economical material, encapsulated calcium carbide (CaC2) (ECC) on the nitrification of soil and applied NH4 +-N in a semiarid subtropical Tolewal sandy loam soil under upland [60% water-filled pore space (WFPS)] and flooded conditions (120% WFPS). Nitrification of the applied 100 mg NH4 +-N kg–1 soil under upland conditions was retarded most effectively (93%) by ECC for up to 10 days of incubation, whereas for longer periods, ATC was more effective. After 20 days, only 16% of applied NH4 +-N was nitrified with ATC as compared to 37% with DCD and 98% with ECC. Under flooded soil conditions, nitrates resulting from nitrification quickly disappeared due to denitrification, resulting in a tremendous loss of fertilizer N (up to 70% of N applied without a NI). Based on four indicators of inhibitor effectiveness, namely, concentration of NH4 +-N and NO3 –-N, percent nitrification inhibition, ratio of NH4 +-N/NO3 –-N, and total mineral N, ECC showed the highest relative efficiency throughout the 20-day incubation under flooded soil conditions. At the end of the 20-day incubation, 96%, 58% and 38% of applied NH4 +-N was still present in the soil where ECC, ATC and DCD were used, respectively. Consequently, nitrification inhibition of applied fertilizer N in both arable crops and flooded rice systems could tremendously minimize N losses and help enhance fertilizer N-use efficiency. These results suggest that for reducing the nitrification rate and resultant N losses in flooded soil systems (e.g. rice lowlands), ECC is more effective than costly commercial NIs. Received: 25 May 2000  相似文献   

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