不同连作年限对薏苡土壤特性、产量和品质的影响

为了探明连作年限对薏苡根际土壤特性、根系形态、产量和品质的影响,以不同连作年限的薏苡为对象,研究其根际土壤性质、根系形态、产量和品质的变化规律及其相关性。结果表明:连作薏苡使土壤逐渐酸化,全氮含量显著升高,全磷、有效磷和速效钾含量显著降低,有机质含量随连作年限的增加逐渐下降,连作6年的土壤碱解氮含量比轮作降低16.32%～33.93%;土壤细菌和放线菌数量明显减少,真菌数量逐渐增加;土壤蔗糖酶、脲酶和酸性磷酸酶活性显著下降,过氧化氢酶活性显著升高,连作6年的土壤过氧化氢酶活性比轮作高出30.18%～38.98%;随着连作年限的增加薏苡总根系长、总根系表面积、根系平均直径和根系总体积呈下降趋势;连作6年薏苡的千粒重、结实率、每穴粒重和每穴粒数显著低于轮作,连作年限每增加一年,薏苡产量减少632.276 kg/hm²,连作6年的薏苡减产44.13%～53.43%;连作薏苡的可溶性糖、赖氨酸和支链淀粉含量降低,连作对粗蛋白和粗脂肪含量的影响不显著。相关性分析结果表明,连作薏苡的土壤有效磷、速效钾、有机质含量以及pH显著影响微生物数量;过氧化氢酶活性与全磷、全钾、有效磷、速效钾含量和pH呈显著负相关,蔗糖酶、脲酶和酸性磷酸酶活性与细菌、放线菌数量以及全磷、全钾、有效磷、速效钾和pH呈显著正相关;土壤理化性质中的有效磷和速效钾含量是影响产量和品质的主要因素。连作导致薏苡根际土壤化学性质和微生物环境恶化,根系发育不良,进而使产量和品质下降。     

连作Ⅰ-107杨树无性系苗圃地的土壤酶活性特征

 为给苗圃地经营和防止地力衰退提供理论依据,以Ⅰ107杨树无性系为试材,研究苗圃地连作育苗对土壤酶活性的影响,并分析土壤酶之间、土壤酶与土壤养分和土壤微生物之间的相关关系。研究结果表明:随着育苗代数的增加,苗圃地土壤酶活性除多酚氧化酶外均呈现出下降趋势,在垂直土壤剖面上,脲酶、过氧化氢酶、过氧化物酶活性均随着土层的加深而降低,多酚氧化酶活性则表现出先增加后减小的趋势。除多酚氧化酶之外,其余3种酶活性之间均呈正相关关系,多酚氧化酶与其他3种酶之间则呈负相关。苗圃地土壤中的有机质、土壤速效N、P、K和微量元素Cu的含量,也随着育苗代数的增加而降低。连作苗圃地土壤脲酶、过氧化氢酶和过氧化物酶活性,与土壤基础肥力有机质、速效N、P、K的相关性,均达到显著或极显著的水平,脲酶和过氧化氢酶活性与微量元素Cu的相关性,也达到显著水平,多酚氧化酶活性与土壤各营养元素含量,呈负相关。随着育苗代数的增加,表层(0～20cm)土壤中各类微生物的数量均呈下降趋势,并且脲酶与放线菌、过氧化氢酶与细菌、放线菌、微生物总量、过氧化物酶与真菌之间的相关性达显著水平,过氧化氢酶与真菌、过氧化物酶与细菌、微生物总量之间的相关性达极显著水平,多酚氧化酶与各类微生物数量之间是负相关关系。     

不同年龄时期石榴园土壤养分、微生物量及酶活性

  目的  明确不同年龄时期石榴园土壤养分、土壤微生物量、土壤酶活性状况,为不同年龄时期的石榴园土壤管理提供参考依据。  方法  采集陕西石榴主产区处于生长期、结果初期和盛果期三个年龄时期的石榴园土样,测定土壤养分、土壤微生物量以及土壤酶活性,并分析它们之间的相关性。  结果  ① 陕西石榴主产区土壤中碱解氮的含量在结果初期和盛果期显著高于生长期,但整体含量均较低;速效磷和速效钾含量随石榴树年龄增加显著递增,且速效磷的含量在各年龄时期均较高,而速效钾的含量仅在生长期偏低。② 微生物数量随石榴树年龄增加逐渐增多,且细菌数量显著递增,而真菌数量和放线菌数量在结果初期和盛果期均显著高于生长期,但在结果初期和盛果期之间无显著性差异。③ 土壤脲酶、蔗糖酶和碱性磷酸酶活性随石榴树年龄显著递增,而过氧化氢酶活性则显著递减。④相关性分析结果表明,土壤脲酶、蔗糖酶和碱性磷酸酶活性与土壤中的细菌和真菌数量正相关,而过氧化氢酶活性则与土壤中的细菌和真菌数量负相关;仅蔗糖酶与放线菌数量显著相关;这四种酶活性均与碱解氮、速效磷以及速效钾含量显著相关;真菌及放线菌数量均与碱解氮、速效磷和速效钾显著相关,而细菌数量与速效磷和速效钾极显著相关,但与碱解氮没有显著相关性。  结论  不同年龄时期的石榴园土壤养分、土壤微生物数量及土壤酶活性具有一定的差异,而且土壤微生物数量及土壤酶活性均与土壤养分密切相关。     

大棚辣椒连作土壤微生物数量、酶活性与土壤肥力的关系

选取不同连作年限的辣椒大棚土壤和相邻露地小麦-辣椒轮作土壤(对照),研究了大棚辣椒连作土壤微生物数量、酶活性与土壤肥力的关系。结果表明,连作土壤养分含量显著高于对照,而pH值显著低于对照;土壤细菌,放线菌数量随连作年限延长呈先增加后降低的趋势并高于对照,而真菌数量不断增加;连作土壤酶活性含量均显著高于对照。土壤细菌数量与土壤有机质、全磷呈显著相关性,真菌数量与土壤养分无显著相关性,放线菌数量、过氧化氢酶、蔗糖酶、脲酶活性与pH值呈显著负相关性,与养分呈显著相关性。土壤全磷、全氮、pH值对微生物数量的影响较大,而全氮、pH值对土壤酶活性的影响较大。     

基于旋耕玉米秸秆还田条件下土壤微生物、酶及速效养分的动态特征

为研究旋耕条件下秸秆还田的腐解机理,设置不同数量秸秆还田处理,分别于玉米拔节期、抽雄期、乳熟中期、完熟期测定土壤微生物数量、土壤酶活性和速效养分含量。结果表明:(1)秸秆还田促进土壤微生物繁殖,提高土壤酶活性,增加碱解氮含量,降低速效磷和速效钾含量;秸秆量为11 250kg/hm~2时真菌、细菌、放线菌数量及蔗糖酶、纤维素酶活性增幅最大;秸秆量为7 500kg/hm~2时脲酶、磷酸酶活性和碱解氮增幅最大,速效磷、速效钾降幅最大。(2)部分土壤微生物数量与土壤酶活性之间存在相关性,播种后40天,土壤真菌、细菌、放线菌数量、纤维素酶活性之间存在正相关,真菌与磷酸酶活性呈负相关;播种后67天,放线菌与磷酸酶、蔗糖酶呈正相关;播种后140天,放线菌与蔗糖酶呈正相关。(3)部分土壤酶活性之间存在相关性,播种后67天,脲酶与纤维素酶、磷酸酶与蔗糖酶之间呈正相关;播种后140天,蔗糖酶与纤维素酶呈正相关,脲酶与蔗糖酶、纤维素酶呈负相关。(4)土壤酶活性与速效养分存在相关性,播种后40,112天的脲酶、67天的纤维素酶、112,140天的磷酸酶与碱解氮含量呈正相关;播种后40天,蔗糖酶与速效钾呈正相关,播种后40,67,112天脲酶活性与速效钾含量呈负相关。(5)碱解氮与速效磷含量呈负相关,播种后40,112,140天的碱解氮与速效钾含量呈负相关。     

衡阳紫色土丘陵坡地不同植被恢复阶段土壤酶活性特征研究

本文以典型的衡阳紫色土丘陵坡地不同植被恢复阶段为研究对象,采用空间代替时间序列方法,选用立地条件基本相似的草坡阶段（Grassplot, GT）、 灌草阶段（Frutex and grassplot,FG）、 灌丛阶段（Frutex, FX）和乔灌阶段（Arbor and frutex, AF）,通过调查取样和实验分析,对不同植被恢复阶段的土壤酶、 养分与微生物及其相关性进行了研究。结果表明, 1）随着恢复阶段的演替,脲酶、 多酚氧化酶、 蔗糖酶与过氧化氢酶的活性显著增加,在每个恢复阶段,脲酶、 多酚氧化酶、 蔗糖酶与过氧化氢酶活性随着土层的加深而逐渐减弱,脲酶与多酚氧化酶、 蔗糖酶与过氧化氢酶活性呈显著正相关关系,蔗糖酶与脲酶和多酚氧化酶呈极显著正相关。 2）随着恢复阶段的演替,土壤养分的时空变化与土壤酶活性的变化趋势基本一致,土壤有机碳、 全氮与碱解氮含量呈上升趋势,土壤pH随植被恢复和演替而降低,随土壤深度的增加而上升,与土壤酶活性的变化趋势相反;脲酶与有机碳、 全氮、 碱解氮呈极显著正相关,与pH呈显著负相关,多酚氧化酶与有机碳、 碱解氮呈极显著正相关,与全氮、 速效磷、 速效钾呈显著正相关,与pH呈显著负相关,蔗糖酶活性与有机碳、 全氮、 碱解氮、 速效磷、 速效钾呈显著正相关。 3）不同恢复阶段土壤细菌数量最多,真菌数量和放线菌数量与细菌数量的变化趋势各不相同;细菌平均数量为AF＞FX＞FG＞GT,真菌数量为 FG＞GT＞FX＞AF,放线菌数量为 GT＞FX＞FG＞AF。4）主成分分析揭示脲酶与多酚氧化酶可作为衡阳紫色土丘陵坡地土壤质量评价的指标。研究结果将丰富该地区植物生态学与恢复生态学的内容,为衡阳紫色土丘陵坡地生态系统的恢复与重建提供了重要依据。     

旱地花生不同土壤类型主要土壤肥力指标季节变异及其相互关系研究

大田条件下,以砂姜黑土和棕壤为对象,研究了花生生育期内土壤主要肥力指标变化特点及相互关系,结果表明:不同土壤类型旱地花生生育期内土壤碱解氮、速效磷和速效钾含量呈逐渐降低趋势,生育中期下降速率明显高于生育前期和后期,与花生对主要营养元素吸收速率一致;土壤微生物数量(细菌、放线菌和真菌)、土壤呼吸速率及主要土壤酶(脲酶、蔗糖酶、酸性磷酸酶和过氧化氢酶)活性随生育进程的推进呈单峰曲线,高峰期多数出现在结荚中期.砂姜黑土细菌、放线菌及3种主要酶活性高于棕壤,真菌数量棕壤高于砂姜黑土;生育后期,棕壤碱解氮含量、速效钾含量、细菌和放线菌数量以及脲酶、蔗糖酶和过氧化氢酶活性下降速率高于砂姜黑土,速效磷含量和酸性磷酸酶活性两种土壤下降速率相近.因此,生育后期肥力下降较快,可能是棕壤花生易发生早衰的主要原因.土壤主要肥力指标间多数呈显著或极显著正相关关系,但不同土壤类型指标间相关性存在一定差异.     

新疆艾比湖地区不同土地利用方式土壤养分、酶活性及微生物特性研究

新疆艾比湖地区在我国内陆荒漠自然生态系统中具有典型性和较高研究价值,通过对不同土地利用方式土壤进行采样和分析,系统地研究和比较了不同土地利用方式土壤酶活性及微生物特性(土壤微生物量和微生物数量)。结果表明:新疆艾比湖不同土地利用方式土壤机械组成不尽一致,黏粒含量占主导地位,粗砂粒含量相对较低,土壤总孔隙度与土壤容重变化趋势相反。不同土地利用方式对土壤养分具有较大影响,不同土地利用方式下土壤养分(有机碳、全氮、全磷)和有效养分(有效磷、有效氮、有效钾、有效锌、有效铁含量)均呈现出一致性规律,大致表现为林地草地耕地未利用地,土壤全磷在不同土地利用方式下差异均不显著(p0.05);与耕地相比,土壤微生物量碳和氮、土壤微生物数量(细菌、真菌和放线菌),土壤酶活性(土壤蔗糖酶、脱氢酶、脲酶、酸性磷酸酶活性)均有明显的增加,大致表现为:林地草地耕地未利用地;相关性分析表明,土壤微生物量碳和氮、细菌、放线菌和真菌数量、蔗糖酶、脱氢酶、脲酶和磷酸酶活性均呈显著或者极显著的负相关(p0.05,p0.01);土壤有机质和全氮与蔗糖酶、脱氢酶、磷酸酶和细菌数量呈极显著正相关(p0.01),土壤有效养分与土壤微生物量碳、细菌数量和蔗糖酶活性呈显著或极显著正相关(p0.05,p0.01),说明土壤微生物量碳仍是有效养分的主要来源,其中土壤容重对土壤微生物量、微生物数量和酶活性贡献为负,土壤养分对土壤微生物量、微生物数量和酶活性贡献为正,这是造成不同土地利用方式土壤微生物量、微生物数量和酶活性差异的重要原因,其中有机质和全氮是土壤微生物量、微生物数量和酶活性的主要养分来源。     

宁夏贺兰山东麓酿酒葡萄基地土壤酶活性

调查了宁夏御马酿酒葡萄基地不同栽培年限下土壤的蔗糖酶、磷酸酶、脲酶、过氧化氢酶的活性,并与土壤的基本理化性质进行了回归分析。结果表明,供试土壤为强碱性反应,耕作施肥对土壤pH和全盐含量影响不显著;土壤有机质、全氮、铵态氮、速效磷、阳离子代换量大都处于最低的六级水平,但肥力随耕种年限的延长显著增加;随栽培年限的延长,表层土壤磷酸酶活性、蔗糖酶和脲酶活性显著增加;蔗糖酶、脲酶活性随剖面深度的加深而显著减小;表土过氧化氢酶活性随栽培年限的延长而显著下降,但不同土地利用下表层以下各层次土壤过氧化氢酶活性总体上高于表层,且差异显著。磷酸酶活性与土壤有机质、全氮、全磷、速效磷、缓效钾、速效钾之间存在着极显著相关关系;磷酸酶活性、蔗糖酶和脲酶活性与土壤有机质、全氮、全磷、速效磷、缓效钾、速效钾之间存在着极显著相关关系;四种酶之间,磷酸酶与脲酶之间存在极显著相关关系,脲酶与蔗糖酶之间存在极显著相关关系。由此表明,磷酸酶、脲酶、蔗糖酶活性的大小可以代表宁夏贺兰山东麓酿酒葡萄栽培区土壤肥力的高低。     

长期定位施肥对土壤酶活性的影响及其调控土壤肥力的作用

为探讨长期施肥条件下土壤酶活性及其与土壤肥力的关系,对褐潮土肥料定位试验田第12年的土壤酶以及土壤养分因子进行了测定和分析。结果表明,NPK与有机肥长期配合施用能明显提高土壤有机质含量,全氮、全磷及速效氮、磷、钾含量,增强土壤转化酶、磷酸酶和脲酶的活性。玉米秸秆有利于提高土壤转化酶活性,而有机肥则主要提高土壤脲酶和磷酸酶活性;采用轮作方式比连作能更好地培肥土壤。土壤酶活性与土壤肥力之间具有很好的相关性,其中,磷酸酶、脲酶、转化酶活性与有机质、全磷、速效磷含量呈显著正相关;磷酸酶与碱解氮、速效钾,脲酶与速效钾,转化酶与碱解氮均呈显著相关。长期施肥不能增强土壤中过氧化氢酶活性,过氧化氢酶与土壤养分之间无明显相关。     

Determination and depletion of residues of carbadox, tylosin, and virginiamycin in kidney, liver, and muscle of pigs in feeding experiments

The results of residue determinations of the growth promotors carbadox, tylosin, and virginiamycin in kidney, liver, and muscle from pigs in feeding experiments are described as well as the analytical methods used. Residues of the carbadox metabolite quinoxaline-2-carboxylic acid were found in liver from pigs fed 20 mg/kg in the diet with a withdrawal time of 30 days. No residues were detected in muscle with zero withdrawal time. The limit of determination was 0.01 mg/kg for both tissues. No residues of virginiamycin and tylosin were found in pigs fed 50 and 40 mg/kg, respectively, in the diet, even with zero withdrawal time. Residues of tylosin of 0.06 mg/kg and below were detected in liver and kidney from pigs fed 200 or 400 mg/kg and slaughtered within 3 h after the last feeding.     

Chemistry, biochemistry, nutrition, and microbiology of lysinoalanine, lanthionine, and histidinoalanine in food and other proteins

Heat and alkali treatments of foods, widely used in food processing, result in the formation of dehydro and cross-linked amino acids such as dehydroalanine, methyldehydroalanine, beta-aminoalanine, lysinoalanine (LAL), ornithinoalanine, histidinoalanine (HAL), phenylethylaminoalanine, lanthionine (LAN), and methyl-lanthionine present in proteins and are frequently accompanied by concurrent racemization of L-amino acid isomers to D-analogues. The mechanism of LAL formation is a two-step process: first, hydroxide ion-catalyzed elimination of H(2)S from cystine and H(2)O, phosphate, and glycosidic moieties from serine residues to yield a dehydroalanine intermediate; second, reaction of the double bond of dehydroalanine with the epsilon-NH(2) group of lysine to form LAL. Analogous elimination-addition reactions are postulated to produce the other unusual amino acids. Processing conditions that favor these transformations include high pH, temperature, and exposure time. Factors that minimize LAL formation include the presence of SH-containing amino acids, sodium sulfite, ammonia, biogenic amines, ascorbic acid, citric acid, malic acid, and glucose; dephosphorylation of O-phosphoryl esters; and acylation of epsilon-NH(2) groups of lysine. The presence of LAL residues along a protein chain decreases digestibility and nutritional quality in rodents and primates but enhances nutritional quality in ruminants. LAL has a strong affinity for copper and other metal ions and is reported to induce enlargement of nuclei of rats and mice but not of primate kidney cells. LAL, LAN, and HAL also occur naturally in certain peptide and protein antibiotics (cinnamycin, duramycin, epidermin, nisin, and subtilin) and in body organs and tissues (aorta, bone, collagen, dentin, and eye cataracts), where their formation may be a function of the aging process. These findings are not only of theoretical interest but also have practical implications for nutrition, food safety, and health. Further research needs are suggested for each of these categories. These overlapping aspects are discussed in terms of general concepts for a better understanding of the impact of LAL and related compounds in the diet. Such an understanding can lead to improvement in food quality and safety, nutrition, microbiology, and human health.     

Detection, accumulation, distribution, and depletion of furaltadone and nifursol residues in poultry muscle, liver, and gizzard

Nitrofurans were broadly used as an extremely effective veterinary antibiotic especially in pig and poultry production farms. Because of fears of the carcinogenic effects on humans, the nitrofurans were banned from use in livestock production in many countries, including the European Union. The present study examines the accumulation, distribution, and depletion of furaltadone and nifursol and of their tissue-bound metabolites [3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ) and 3,5-dinitro-salicylic acid hydrazine (DNSAH), respectively, in poultry edible tissues (muscle, liver, and gizzards) following administration to chickens of therapeutic and subtherapeutic concentrations of both compounds. Nitrofurans determination was performed by high-performance liquid chromatography-diode array detection and liquid chromatography-tandem mass spectrometry, respectively, for feeds and for poultry tissues. Furaltadone and nifursol, in very low concentrations, were found in samples of muscle, liver, and chicken's gizzard collected from slaughtered animals after 5 weeks of treatment and no withdrawal time period. When a withdrawal time period of 3 weeks was respected, no detectable nitrofuran parent compounds was observed in all of the studied matrices. For AMOZ, concentrations of 270 μg/kg in meat, 80 μg/kg in liver, and 331 μg/kg in gizzard were determined after administration of a medicated feed with furaltadone (132 mg/kg), 3 weeks after withdrawal of treatment. For DNSAH, the concentration values obtained are much lower than those observed for AMOZ. For meat, liver, and gizzard, DNSAH concentrations of 2.5, 6.4, and 10.3 μg/kg, respectively, were determined, after administration of a medicated feed with nifursol (98 mg/kg), 3 weeks after withdrawal of treatment. The gizzard could be considered a selected matrix for nitrofuran residues evaluation in poultry, due to its capacity of retaining either nitrofuran parent compounds or metabolites in higher concentrations, regardless of the administered dose or of the respected withdrawal time period.     

Occurrence, sensory impact, formation, and fate of damascenone in grapes, wines, and other foods and beverages

Among plant-derived odorants, damascenone is one of the most ubiquitous, sometimes occurring as an apparent natural product but more commonly occurring in processed foodstuffs and beverages. It has been widely reported as a component of alcoholic beverages, particularly of wines made from the grape Vitis vinifera . Although damascenone has one of the lowest ortho- and retronasal detection thresholds of any odorant, its contribution to the sensory properties of most products remains poorly understood. Damascenone can be formed by acid-catalyzed hydrolyses of plant-derived apocarotenoids, in both aglycon and glycoconjugated forms. These reactions can account for the formation of damascenone in some, but not all, products. In wine, damascenone can also be subject to degradation processes, particularly by reaction with sulfur dioxide.     

Screening and quantitation of ochratoxin A in corn, peanuts, beans, rice, and cassava

To answer the need for simple, economical, rapid methods for mycotoxins, a procedure for screening and quantitation of ochratoxin A was developed. A methanol-aqueous KCl extraction is used, followed by cleanup with clarifying agents and partition into chloroform. Part of the chloroform extract is used for screening and the other part for quantitation by thin layer chromatography (TLC). The screening procedure takes 40 min, using a silica gel/aluminum oxide minicolumn developed for this purpose. The limits of detection are 80 and 10 micrograms/kg, respectively, for minicolumn screening and TLC quantitation. Ammonium sulfate is efficient in cleaning samples of corn and cassava; cupric sulfate is better with peanuts, beans, and rice. Tests were conducted on triplicate spiked samples of yellow corn meal, raw peanuts, dried black beans, polished rice, and cassava flour at different levels (400, 200, 80, 40, and 10 micrograms/kg). Recoveries ranged from 86 to 160% and the coefficients of variation ranged from 0 to 26%.     

Concentrations of Ag, In, Sn, Sb and Bi, and their chemical fractionation in typical soils in Japan

We determined concentrations of Ag, In, Sn, Sb and Bi, and fractionated them by sequential extraction procedures, in five Japanese soils: Andosol‐1 (grassland), Andosol‐2 (forest), Cambisol (forest), Fluvisol (vegetable garden) and Regosol (forest). Average concentrations of Ag, In, Sn, Sb and Bi were 0.17 ± 0.08, 0.081 ± 0.019, 2.2 ± 0.5, 0.83 ± 0.32 and 0.32 ± 0.12 mg kg^?1, respectively. Average distributions of the chemical fractions (omitting those with an abundance < 5%) were: Ag, residual (60%) > H₂O₂‐extractable, organically bound (H₂O₂‐Org) (18%) > metal–organic complex‐bound (Me‐Org) (10%) > amorphous metal oxide‐bound (am‐MeOx) (8.3%); In, residual (61%) > H₂O₂‐Org (12%) > Me‐Org (8.7%) ≥ crystalline Fe oxide‐bound (cr‐FeOx) (8.2%) > am‐MeOx (7.4%); Sn, residual (40%) > Me‐Org (19%) > carbonate‐bound (12%) > cr‐FeOx (9.0%) > H₂O₂‐Org (7.8%) > am‐MeOx (6.9%); Sb, residual (34%) > Me‐Org (18%) > am‐MeOx (16%) > cr‐FeOx (8.9%) ≥ H₂O₂‐Org (8.7%) > easily reducible metal oxide‐bound (re‐MeOx) (6.8%) > carbonate‐bound (6.1%); Bi, am‐MeOx (26%) ≥ H₂O₂‐Org (26%) > Me‐Org (19%) > residual (17%) > cr‐FeOx (12%). Proportions of the mobilizable (exchangeable + carbonate‐bound + Me‐Org + re‐MeOx) metal fractions were in the order Sn ≥ Sb > Bi > Ag ? In, and Cambisol > Andosol‐2 > Regosol > Andosol‐1 > Fluvisol. The proportions were predicted by multiple regression equations including pH, surface area, C contents, cation exchange capacity and clay content of the soils as independent variables (R² > 0.96, P < 0.02).     

Ontogenic variation in nitrogen fixation and accumulation of nitrogen in mungbean,blackgram, cowpea,and groundnut

Ontogenic variations in N₂ fixation and accumulation of N by the mungbean (Vigna radiata L. Wilczek), blackgram (Vigna mungo L. Hepper), cowpea (Vigna unguiculata L. Walp.), and groundnut (Arachis hypogaea L.) were studied by a ¹⁵N-dilution technique. Pots filled with 7 kg of red yellow podzolic soil were used. Samples were taken 20, 40, 60, and 80 days after emergence which approximately corresponded to preflowering, flowering, early/mid-pod filling and late pod filling stages, respectively. During early growth (up to 40 days after emergence), the carryover of seed N accounted for a considerable fraction of the total plant N in the legumes, the highest being in the groundnut. With a correction for carryover, the groundnut derived over 45% of its N content from the atmosphere 20 days after emergence whereas the corresponding figures were 33% for the blackgram and about 28% for the cowpea and mungbean. Between flowering and early pod fill, there was a rapid increase in N₂ fixation in all legumes except in groundnut which showed highest fixation from 60 to 80 days after emergence. In the mungbean, N₂ fixation and uptake of soil N were insignificant 60 days after emergence while in other legumes these processes continued beyond this time. All legumes derived about 90% of their N from atmosphere by 80 days after emergence. However, due to considerable interspecific differences in total N yield the final amount of N₂ fixed showed an appreciable variation among legumes. It was highest in the groundnut (443 mg N plant^-1) followed by the cowpea (385), blackgram (273), and mungbean (145), respectively. The groundnut maintained nodules until the late pod filling stage while in other legumes, nodules senesced progressively following the mid-pod filling stage. During pod filling there was a net mobilization of N from vegetative tissues to developing pods in the mungbean, which amounted to about 20% of N in seeds. This mobilization was not evident in other legumes.