盆栽和田间条件下土壤15N标记肥料氮的转化

利用¹⁵N在盆栽条件下研究了铵的矿物固定作用对肥料氮在三种土壤中转化的影响.结果表明,红壤性水稻土不固定肥料铵,但在白土和夹沙土中,56-77%的肥料氮被土壤矿物所固定,这些“新固定”的固定态铵的有效性很高,其中90%以上在30-50天内即被水稻所吸收,或者为微生物所利用转变为生物固定态氮.生物固定态氮对当季作物的有效性远较“新固定”的固定态铵的低.田间微区试验的结果还表明,甚至第二、三季作物吸收的残留肥料氮中,20-86%的氮也系来自固定态铵.作者认为,对具有较强固铵能力的土壤来说,只有了解铵的矿物固定作用,才能正确了解肥料氮的其它转化过程.     

利用15N标记土壤测定某些豆科植物的固N量

共生固氮是土壤氮素的主要来源之一。它在保持土壤氮素肥力和保证农业的持续发展中起着重要的作用。     

反硝化细菌法测定土壤NO2--15N丰度的方法优化

NO₂^-是土壤中多个氮转化过程的关键中间产物,具有浓度低、转化快的特点。反硝化细菌法与质谱技术相结合,已广泛用于NO₃^-或NO₂^-的¹⁵N同位素分析。本文旨在优化现有Stenotrophomonas nitritireducens反硝化细菌法的培养和反应条件,实现对土壤浸提液中NO₂^--¹⁵N丰度的专一、快速、准确测定。结果表明,使用种子液好氧摇培与单菌落微氧培养对NO₂^-样品的¹⁵N同位素测定无显著差异,种子液可保证不同批次菌体的稳定性,好氧培养可将培养时间从7～8d缩短至12～15h。高纯N₂或He气吹扫0.5h均能有效去除O₂和空白杂质氮,但N₂吹扫成本更低。转移N₂O气体至干燥气瓶,不影响测定结果的准确性和精密...     

15N-绿肥和15N-硫铵对土壤有机无机复合体中碳氮的影响

应用¹⁵N示踪技术研究了硫铵和绿肥对土壤碳、氮的影响。结果表明,它们能增加土壤重组碳、氮和紧结态碳、氮,重组中的¹⁵N集中于紧结态腐殖质中,碳、氮的累积量都是施绿肥比施硫铵的为多。各施肥处理的松结态碳、氮在稻季累积,麦季释放,紧结态氮有一部分释放。氮素的下降幅度是松结态氮大于紧结态氮,绿肥处理大于硫铵处理,¹⁵N量大于全氮量。     

N2O产生法测定土壤无机态氮15N丰度

用化学方法分别将土壤中微量的铵、硝酸盐和亚硝酸盐转化为N2O气体,然后用带自动预浓缩装置的同位素比值质谱仪测定N2O中的15N丰度.N2O中的15N丰度测量值完全符合铵、硝酸盐和亚硝酸盐的15N参考值.方法快速、简单和准确,不受空气氮的污染.特别是方法的检测限很低,每批次样品中只需含5～ 20μg N.它将有助于土壤氮素的矿化作用、硝化作用和反硝化作用的研究.     

应用15N核磁共振技术对苯聚合物结合蛋白中氮形态的研究

Phenolic polymers synthesized by reactions by reactions of p-benzoquinone with 15N-labelled protein or (15NH4)2SO4 were studied by using 15N CP-MAS NMR technique in combination with chemical approaches.Results showed that more than 80% of nitrogen in quinone-protein polymers was in the form of amide with some present as aromatic and /or aliphatic amine and less than 10% of nitrogen occurred as heterocyclic N.The nitrogen distribution in the non-hydrolyzable residue of the quinone-protein polymers was basically similar to that of soil humic acid reported in literature with the exception that a higher proportion of N as heterocyclic N and aromatic amine and a lower proportion of N as amide and aliphatic amine were found in the former than in the latter,More than 70% of total nitrogen in quinone-(NH4)2OS4 polymer was acid resistant ,of which about 53% occurred as pyrrole,nitrile and imion type N.The possible roles of the reactions of phenols or quinones with proteins in the formation of humic acid.especially the non-hydrolyzable nitrogen in humicacid,are discussed.     

15N标记有机肥的制备及其质量

近年来示踪技术迅速发展,利用同位素示踪法研究氮肥在作物-土壤体系中的去向也是有效的方法。尤其是监测氮肥的时空分布时显得更为适宜。现今的肥料施用结构中,有机肥的施用量较高,研究有机肥的去向也是大势所趋。但15N标记有机肥很难买到,因此必须通过15N标记的化肥进行制备。     

施入~(15)N标记氮肥在长期不同培肥土壤的残留及其利用

采用盆栽试验和短期矿化培养相结合的方法,研究了施入15N标记氮肥(+N)及其与秸秆配施(+1/2N+1/2S)在3种长期(19年)不同培肥土壤(即:No-F,长期不施肥土壤;NPK,长期施用NPK化肥土壤;MNPK,长期有机无机肥配施土壤)中的残留及其矿化和作物吸收特性。结果表明,第一季小麦收获后,+1/2N+1/2S处理下三供试土壤和+N处理下的NPK和MNPK土壤残留肥料氮(残留15N)中有82.6%~95.1%以有机态存,而+N处理下No-F土壤残留15N有47.7%以矿质态存在。经过28 d矿化培养后,与NPK土壤相比,MNPK土壤氮素净矿化量显著增加,增幅为39%~49%;NPK和MNPK土壤残留肥料氮(残留15N)矿化量为1.23~1.90 mg kg-1,占总残留15N的2.78%~5.53%,均显著高于No-F土壤。与+N处理相比,+1/2N+1/2S处理显著提高了3供试土壤氮素净矿化量,但两施肥处理对NPK和MNPK土壤残留15N矿化量无显著影响。+N处理下No-F土壤残留15N的利用率为20%,显著高于NPK(9%)和MNPK(12%)土壤。两种施肥处理下,MNPK土壤残留15N的利用率均显著高于NPK土壤。短期培养期间土壤氮素矿化量和第二季小麦生育期作物吸氮量呈显著性正相关,而残留15N矿化量和第二季小麦吸收残留15N量间无显著性相关关系。长期有机无机配施可以提高土壤残留肥料氮的矿化量及有效性。     

由木糖和15N标记的甘氨酸形成的美拉德氏聚合物的氮素形态

Water-soluble,nondialyzable Maillard polymers were prepared by reacting D-xylose with ^15N-glycine (and /or glycine)at 6８℃ and pH 8.0 at equimolar concentrations of 1,0.5 and 0.1 mol L^-1,respectively, for 13 days and partitioned into acid-insoluble(MHA) and acid-soluble(MFA) fractions.The nitrogen froms in these polymers were studied by using the ^15N cross polartisation-magic angle spinning nuclear magnetic resonance(CPMAS NMR) technique in combination with chemical methods .The ^15N nuclear magnetic resonance(NMR) data showed that while the yield,especially the MHA /MFA ratio,varied considerably with the concentrations of the reactants,the nitrogen distribution patterns of these polymers were quite similar. From 65% to 70% of nitrogen in them was in the secondary amide and /or indole form with 24%-25% present as aliphatic and /or aromatic amines and 5% to 11% as pyrrole and /or pyrrole-like nitrogen,More than half (50%-77%) of the N in these polymers were nonhydrolyzable,The role of Maillard reacion in the formation of nonhydrolyzable nitrogen in soil organic matter is discussed.     

大田条件下草本及灌木豆科植物固氮能力的评价

Natural ¹⁵N abundance method was used in this study to investigate the N₂-fixing capacities of several herbaceous and shrub legumes by a field experiment. For herbaceous legumes, the results were in consistent with those obtained by a pot experiment. Crotalaria mucronata Desv. had a higher N₂-fixing capacity than Vigna sinensis (L.) Savi. For shrub legumes, N₂-fixing capacity under field condition was slightly different from that in pot experiment. These results demonstrated that the natural ¹⁵N abundance method was applicable to evaluating N₂-fixing capacities of herbaceous and shrub legumes, and that pot experiment was suitable for evaluating the N₂-fixing capacities of not only herbaceous legumes but also shrub legumes. Leguminous N₂-fixing plants differed in response to phosphorus fertilization. Phosphorus fertilizer application greatly increased the percentage of nitrogen derived from air (% N dfa) and total amount of N₂ fixed by Lespedeza formosa (Vog.) Koehne (Jiangxi). Phosphorus fertilizer showed no significant effect on the N₂-fixing percentage of Cajanus cajan (L.) Millsp. but increased its total biomass, thus increasing the total amount of N₂ fixed.     

固态13C和15N核磁共振法研究15N标记土壤的腐殖质组分

Five humic fractions were obtained from a uniformly ^15N-labelled soil by extraction with 0.1 mol L^-1 Na4P2O7,0.1mol L^-1 NaOH ,and HF/HCl-0.1 mol L^-1 NaOH,consecutively,and analyzed by ^13C and ^15N CPMAS NMR (cross polarization and magic angle spinning nuclear magnetic resonace).Compared with those of native soils humic fractions studied as a whole contained more alkyls ,methoxyls and O-alkyls,being 27%-36%,17%-21%and 36%-40%,respectively,but fewer aromatics and carboxyls(bein 14%-20% and 13%-90%,respectively),Among those humic fractions ,the humic acid(HA)and fulvic acid(FA) extracted by 0.1 mol L^-1 Na4P2O7 contained slightly more carboxyls than corresponding humic fractions extracted by 0.1 mol L^-1 NaOH ,and the HA extacted by 0.1 mol L^-1 NaOH after treatment with HF/HCl contained the least aromatics and carboxyls.The distribution of nitrogen functional groups of soil humic fractions studied was quite similar to each other and also quite similar to that of humic fraction from native soils.More than 75% of total N in each fraction was in amide from,with 9%-13% present as aromatic and /or aliphatic amines and the remainder as heerocyclic N.     

Isotopic fractionation during N2 fixation by four tropical legumes

To quantify the contribution of biological nitrogen fixation (BNF) to legume crops using the ¹⁵N natural abundance technique, it is necessary to determine the ¹⁵N abundance of the N derived from BNF—the B value. In this study, we used a technique to determine B whereby both legume and non-N₂-fixing reference plants were grown under the same conditions in two similar soils, one artificially labelled with ¹⁵N, and the other not. The proportion of N derived from BNF (%Ndfa) was determined from the plants grown in the ¹⁵N-labelled soil and it was assumed that the %Ndfa values of the legumes grown in the two soils were the same, hence the B value of the legumes could be calculated. The legumes used were velvet bean (Mucuna pruriens), sunnhemp (Crotalaria juncea), groundnut (Arachis hypogaea) and soybean (Glycine max) inoculated, or not, with different strains of rhizobium. The values of %Ndfa were all over 89%, and all the legumes grown in unlabelled soil showed negative δ¹⁵N values even though the plant-available N in this soil was found to be approximately +6.0‰. The B values for the shoot tissue (B_s) were calculated and ranged from approximately −1.4‰ for inoculated sunnhemp and groundnut to −2.4 and −4.5‰ for soybean inoculated with Bradyrhizobium japonicum strain CPAC 7 and Bradyrhizobium elkanii strain 29W, respectively. The B (B_wp) values for the whole plants including roots, nodules and the original seed N were still significantly different between the soybean plants inoculated with CPAC 7 (−1.33‰) and 29W (−2.25‰). In a parallel experiment conducted in monoxenic culture using the same soybean variety and Bradyrhizobium strains, the plants accumulated less N from BNF and the values were less negative, but still significantly different for soybean inoculated with the two different Bradyrhizobium strains. The results suggest that the technique utilized in this study to determine B with legume plants grown in soil in the open air, yields B values that are more appropriate for use under field conditions.     

Emission of N2O, N2 and CO2 from soil fertilized with nitrate: effect of compaction, soil moisture and rewetting

Soil compaction and soil moisture are important factors influencing denitrification and N₂O emission from fertilized soils. We analyzed the combined effects of these factors on the emission of N₂O, N₂ and CO₂ from undisturbed soil cores fertilized with (150 kg N ha⁻¹) in a laboratory experiment. The soil cores were collected from differently compacted areas in a potato field, i.e. the ridges (ρ_D=1.03 g cm⁻³), the interrow area (ρ_D=1.24 g cm⁻³), and the tractor compacted interrow area (ρ_D=1.64 g cm⁻³), and adjusted to constant soil moisture levels between 40 and 98% water-filled pore space (WFPS).High N₂O emissions were a result of denitrification and occurred at a WFPS≥70% in all compaction treatments. N₂ production occurred only at the highest soil moisture level (≥90% WFPS) but it was considerably smaller than the N₂O-N emission in most cases. There was no soil moisture effect on CO₂ emission from the differently compacted soils with the exception of the highest soil moisture level (98% WFPS) of the tractor-compacted soil in which soil respiration was significantly reduced. The maximum N₂O emission rates from all treatments occurred after rewetting of dry soil. This rewetting effect increased with the amount of water added. The results show the importance of increased carbon availability and associated respiratory O₂ consumption induced by soil drying and rewetting for the emissions of N₂O.     

Influence of arbuscular mycorrhizae and phosphorus fertilization on growth, nodulation and N2 fixation (15N) inMedicago sativa at four salinity levels

The rose of an isolate of the arbuscular mycorrhizal (AM) fungusGlomus mosseae in the protection ofMedicago sativa (+Rhizobium meliloti) against salt stress induced by the addition of increasing levels of soluble salts was studied. The interactions between soluble P in soil (four levels), mycorrhizal inoculum and degree of salinity in relation to plant growth, nutrition and infective parameters were evaluated. Salt stress was induced by sequential irrigation with saline water having four concentrations of three salts (NaCl, CaCl₂, and MgCl₂).¹⁵N-labelled ammonium sulphate was added to provide a quantitative estimate of N₂ fixation under moderate to high salinity levels. N and P concentration and nodule formation increased with the amount of plant-available P or mycorrhizal inoculum in the soil and generally declined as the salinity in the solution culture increased from a moderate to a high level. The mycorrhizal inoculation protected the plants from salt stress more efficiently than any amount of plant-available P in soil, particularly at the highest salinity level applied (43.5 dS m^–1). Mycorrhizal inoculation matched the effect on dry matter and nutrition of the addition in the soil of 150 mg P kg^–1. Nevertheless the highest saline solution assayed (43.5 dS m^–1) affected more severely plants supplemented with phosphorus than those with the addition of mycorrhizal inoculum. Such a saline-depressing effect was 1.5 (biomass), 1.4 (N) and 1.5 (P) times higher in plants supplied with soluble phosphate than with AM inoculum. Mechanisms beyond those mediated by P must be involved in the AM-protectioe effect against salinity. The¹⁵N methodology used allowed the determination of N₂ fixation as influenced by different P applications compared to mycorrhizal inoculation. A lack of correlation between nodule formation and function (N₂ fixation) was evidenced in mycorrhizal-inoculated plants. In spite of the reduced activity per nodule in mycorrhizal-inoculated In spite of the reduced activity per nodule in mycorrhizal-inoculated plants, the N contents determined indicated the highest acquisition of N occurred in plants with the symbiotic status. Moreover, N and P uptake increased while Ca and Mg decreased in AM-inoculated plants. Thus P/Ca ratios and cation/anion balance in general were altered in mycorrhizal treatments. This study therefore confirms previous findings that AM-colonized plants have optional and alternative mechanisms available to satisfy their nutritive requirements and to maintain their physiological status in stress situations and in disturbed ecosystems.     

Nitrogen accumulation in three legumes and two cereals with emphasis on estimation of N2 fixation in the legumes by the natural 15N-abundance technique

Summary N accumulation and natural ¹⁵N abundance in three legumes (groundnuts, cowpeas, and soybeans) and in two cereals (sorghum and maize) were investigated over two seasons in Alfisols with and without N fertilization. Using the N uptake and natural ¹⁵N abundance of non-nodulating plants as the indication of N derived from soil and fertilizer, the per cent N derived from atmospheric N₂ was calculated for nodulated plants. In the first experiment, the groundnut genotype contained 85% atmosphere-derived N, but the percentage decreased with N application. Estimates of atmosphere-derived N by the N-difference and ¹⁵N-abundance techniques gave identical results. The percentages of atmosphere-derived N estimated by the two methods at different stages of groundnut growth were also similar. In the second experiment, atmosphere-derived N was estimated in plants grown with 0–200 kg ha^-1 applied N. The estimated atmosphere-derived N ranged from 42% to 61% for groundnuts from 33% to 77% for cowpeas, and from 24% to 48% for soybeans, depending on the amount of N applied. Inoculation with a Bradyrhizobium strain increased the percentage of atmospherederived N in soybean plants grown without any fertilizer N. The natural ¹⁵N abundance of sorghum and maize was very close to that of the non-nodulating groundnut, suggesting that these cereals can be used as reference plants in the estimation of atmosphere-derived N by the natural ¹⁵N-abundance method.ICRISAT Journal Article No. 876     

利用15N2直接标记法研究水稻种植对稻田固氮量和固氮活性的影响

稻田固氮对土壤维持肥力有着重要的作用,但水稻种植与固氮菌及其活性之间的关系尚不清楚。本试验利用¹⁵N₂直接标记法测定了下位砂姜土发育的简育水耕人为土在种水稻和不种水稻条件下的生物固氮量,及其在土壤不同层次(0～1、1～5、5～15 cm)和水稻中的分配,并通过实时荧光定量PCR技术测定了土壤中固氮菌nifH DNA及RNA基因数量。结果表明:种水稻处理显著提高了土壤各层固氮量,尤其提高了1～5 cm和5～15 cm土层土壤固氮量对总固氮量的贡献;种水稻处理的总固氮量是不种水稻处理的10.3倍;水稻植株中生物固定的氮占总固氮量的31.48%;在0～1 cm土层,种水稻处理显著提高了nifH RNA基因数量,而对nifH DNA基因数量的增加不显著。可见,水稻种植没有增加固氮菌的数量,稻田固氮量的增加是因为水稻种植极大地促进了固氮菌nifH基因的表达,提高了固氮菌的固氮活性。     

Estimating N2 fixation by field-grown lupins (Lupinus angustifolius L.) using soil and plant 15N enrichment

Summary Biological N₂ fixation was estimated in a field experiment following the addition of NH₄Cl or KNO₃ to unconfined microplots (1.5 m²) at 2.5 g N m^-2 (10 atom% ¹⁵N). A model of total N and ¹⁵N accumulation in lupins and decreasing ¹⁵N enrichment in the KCl-extractable soil-N pool (0–0.15 m depth) was used to estimate the proportion of N in lupins derived from biological N₂ fixation. Estimates of N₂ fixation derived from the model were compared with ¹⁵N isotope-dilution estimates obtained using canola, annual ryegrass, and wheat as nonfixing reference plants. Biomass, total N accumulation, or ¹⁵N enrichment in the lupin and reference crops did not differ whether NH _inf4 ^sup+ or NO _inf3 ^sup- was added as the labelled inorganic-N source. The decrease in soil ¹⁵N enrichment was described by first-order kinetics, whereas total N and ¹⁵N accumulation in the lupins were described by logistical equations. Using these equations, the uptake of soil N by lupins was estimated and was then used to calculate fixed N₂. Estimates of N₂ fixation derived from the model increased from 0 at 50 days after sowing to a maximum of 0.79 at 190 days after sowing. Those based on the ¹⁵N enrichment of the NO _inf3 ^sup- pool were 10% higher than those based on the mineral-N pool. ¹⁵N isotope-dilution estimates of N₂ fixation ranged from 0.37 to 0.55 at 68 days after sowing and from 0.71 to 0.77 at 190 days after sowing. Reference plant-derived values of N₂ fixation were all higher than modelled estimates during the early states of growth, but were similar to modelled estimates at physiological maturity. The use of the model to estimate N₂ derived from the atmosphere has the intrinsic advantage that the need for a non-fixing reference plant is avoided.     

Nitrogen fixation and beneficial effects of some grain legumes and green-manure crops on rice

Studies were conducted on paddy soils to ascertain N₂ fixation, growth, and N supplying ability of some green-manure crops and grain legumes. In a 60-day pot trial, sunhemp (Crotalaria juncia) produced a significantly higher dry matter content and N yield than Sesbania sesban, S. rostrata, cowpeas (Vigna unguiculata), and blackgram (V. mungo), deriving 91% of its N content from the atmosphere. Dry matter production and N yield by the legumes were significantly correlated with the quantity of N₂ fixed. In a lowland field study involving sunhemp, blackgram, cowpeas, and mungbean, the former produced the highest stover yield and the stover N content, accumulating 160–250 kg N ha^-1 in 60 days, and showed great promise as a biofertilizer for rice. The grain legumes showed good adaptability to rice-based cropping systems and produced a seed yield of 1125–2080 kg ha^-1, depending on the location, species, and cultivar. Significant inter- and intraspecific differences in the stover N content were evident among the grain legumes, with blackgram having the highest N (104–155 kg N ha^-1). In a trial on sequential cropping, the groundnut (Arachis hypogaea) showed a significantly higher N₂ fixation and residual N effect on the succeeding rice crop than cowpeas, blackgram, mungbeans (V. radiata), and pigeonpeas (Cajanus cajan). The growth and N yield of the rice crop were positively correlated with the quantity of N₂ fixed by the preceding legume crop.     

N2 fixation and growth of legumes as affected by sulphur fertilization

The influence of three sulphur application rates in combination with two nitrogen application rates on N₂ fixation and growth of different legumes was investigated. N was applied as N-labelled ¹⁵NH₄ ¹⁵NO₃. The ¹⁵N isotope dilution technique was used to estimate N₂ fixation. At both N increments dry matter yield was highest with high S supply. Independently of the N supply, the high S application rate resulted in a significantly higher N accumulation, which was mainly caused by a higher N₂ fixation rate. With the grain legumes the weight of nodules was increased by the high S application rate. The higher number of nodules per pot with optimum S supply was the result of a better root growth. Rates of acetylene reduction correlated significantly with S supply.