通风方式对柴油污染土壤生物通风修复效果的影响研究

生物通风法被广泛应用于不饱和土壤中挥发性有机物的去除,具有高效、费用低等优点。以黄壤为实验土样,柴油为污染物,采用室内一维土柱实验模拟生物通风过程,研究了抽提和注入两种通风方式下柴油的去除效果及规律。结果表明,两种通风方式的去除规律大致相同,抽提方式的去除速度要比注入快,但最终去除率仅比注入高2.28%;每日通风前后及通风过程中测定的土柱总出气口中总挥发性有机化合物(TVOC)值的变化规律也基本相同,只是通风后TVOC值相对较高;在一天8h的通风过程中,每隔1,2,3h测定的TVOC值波动变化的程度为TVOC1h > TVOC2h > TVOC3h;土壤中有效磷和速效氮的含量与柴油生物降解效率密切相关。     

外源菌群及与植物联合修复华北中度石油污染土壤效果研究

为探讨不同微生物菌群对华北地区中度石油污染土壤的修复效果,在实验室模拟条件下分别进行优势外源石油降解菌群的筛选和优势菌群与植物联合修复试验。结果显示:4种外源石油降解菌群中,PDC-3菌群对中度石油污染土壤总石油烃(TPH,total petroleum hydrocarbons)去除率为84.07%,在各菌群中效果最优;该优势菌群与植物联合修复中度石油污染土壤比单独使用优势菌群修复可获得更好的效果,优势菌群与黑麦草联用及优势菌群与紫花苜蓿联用120 d TPH的去除率分别为91.58%和89.30%,修复后土壤中TPH含量均小于500 mg/kg;同时优势菌群与黑麦草联合修复在90 d即可去除89.32%的土壤TPH,相比选用紫花苜蓿可有效缩短修复周期;优势菌群对土壤TPH的去除起主要作用,其贡献率远高于土著微生物菌群或植物的贡献率;植物对土壤TPH去除的贡献率为4.09%～6.48%,且其作用主要发生在修复过程的中后期;优势菌群单独使用或与植物联合修复中度石油污染土壤120 d均可有效去除C10～C12及C22～C40石油烃组分,去除率为85.14%～100.00%;然而,C13～C21石油烃组分含量表现出阶段性的积累效应;除对土壤石油烃的去除作用外,使用优势菌群进行生物修复存在一定的调节土壤pH、增加土壤肥力,且有利于恢复修复后的土壤功能。     

强化生物通风修复柴油污染土壤影响因素的正交实验

生物通风是继SVE后又一项主要的生物修复技术,在石油污染土壤修复中拥有广阔的前景。为寻求最佳修复效果的最优组合,采用生物通风修复柴油污染土壤的正交土柱实验,对影响生物通风修复效果的5个主要因素（污染强度、土壤含水率、C：N：P、通风的孔隙体积数、通风方式）进行了定量化。结果表明,利用强化生物通风可以在柴油污染土壤的治理中取得较好的效果;方差分析各因素均无显著性影响;极差分析得到影响强化生物通风柴油去除效果的最主要因素为土壤含水率、污染强度,次主要因素为C：N：P、通风的孔隙体积数,而通风方式对去除率的影响很小;在实验的不同阶段有些因素的最优水平有不同程度的改变,总体来说各因素的最佳水平分别为：土壤含水率为4．88％,污染强度为40000mg·kg^-1,C：N：P为100：20：1,通风的孔隙体积数为4,而通风方式的两种水平对去除率的影响相差不大。     

土壤气相抽提技术修复柴油污染场地示范研究

土壤气相抽提(SVE)是一种广泛应用于石油类污染土壤修复工程中的原位修复技术,在广东某柴油污染场地开展SVE技术修复示范工程,探讨SVE技术对此类污染场地的修复效果。结果表明:经过3个多月的修复,土壤中总石油烃的最高去除率达64.88%,在试验进行50d后高浓度的挥发性有机物基本被去除,中低浓度污染物仍然存在,土壤中有效磷和速效氮含量与污染物的生物降解作用相关。为缩短修复时间、降低成本,应将SVE与生物通风技术相结合,并采用相应的强化措施(如添加菌剂和营养物质等),以期获得更高的修复效果。     

茶皂素对潮土重金属污染的淋洗修复作用

为了探讨茶皂素淋洗修复土壤重金属污染的可行性,该文采用振荡提取和土柱淋洗的方法,研究了茶皂素对污染土壤中重金属的去除作用。结果表明,茶皂素溶液的浓度和土壤的pH值对重金属去除率有明显影响。土柱淋洗试验中,采用质量分数7%茶皂素溶液作淋洗液,pH 5.0±0.1、土液质量体积比1：4为最佳淋洗修复条件,此时,Pb、Cd、Zn、Cu的去除率分别为6.74%、42.38%、13.07%、8.75%,去除率的大小顺序为Cd＞Zn＞Cu＞Pb。茶皂素淋洗能有效去除酸溶态和可还原态的重金属,从而大大降低了重金属的环境风险,同时说明茶皂素用于土壤重金属污染淋洗修复有较大潜力。     

油污胁迫下土壤微生物群落结构对外源施用玉米秸秆生物质炭的响应

[目的]分析外源施用玉米秸秆生物质炭对石油污染土壤酶活性和微生物群落结构的影响方式,旨在为黄土高原陇东地区油污土壤生态修复提供新的土壤调理剂。[方法]对轻度(5%)和重度(20%)油污土壤分别实施了玉米秸秆生物炭(B)、金盏菊(J)和金盏菊+玉米秸秆生物炭(JB)3种处理方式,采用常规方法测定了不同处理组间土壤总石油烃(TPH)去除率、酶活性和土壤微生物群落结构。[结果]①轻度污染时土壤总石油烃(TPH)去除率为JB_5(61.95±1.39%)最高,重度污染时为JB_(20)(56.44±1.89%)最高(p0.05);②外源施用玉米秸秆生物质炭能有效增加轻重两种油污浓度的土壤脱氢酶和多酚氧化酶活性;③油污浓度由5%增至20%,两种生物质炭参与的处理组(JB_(20)和B_(20))土壤微生物群落结构组成差异相对较小(p0.05);④非度量多维尺度(NMDS)分析结果显示,土壤脱氢酶、多酚氧化酶、Chao1指数和Shannon指数是驱动J_5,B_5,B_(20),JB_5和JB_(20)处理组土壤微生物群落结构分异于CK_5,CK_(20)和J_(20)处理组的主要环境因子。[结论]轻重两种油污浓度胁迫时外源施用玉米秸秆生物质炭可显著增加土壤脱氢酶和多酚氧化酶活性,驱动土壤微生物群落结构变化,从而提高了土壤TPH去除率,因此陇东黄土高原地区油污土壤场地生态修复时可选用玉米秸秆生物质炭作为土壤调理剂。     

通风速率对土壤中四氯化碳污染物去除效率的影响研究

某重要岩溶地下水源地受到四氯化碳的严重污染,为此采用土柱通风试验模拟土壤气相抽提（SVE）净化四氯化碳污染物的过程,对通风速率为40mL·min-1和70mL·min-1两种条件下土壤四氯化碳的去除过程进行了试验模拟研究。结果表明,土柱通风能有效去除土壤中的四氯化碳污染物,通风条件下土壤中四氯化碳的去除过程符合一级反应动力学,土壤中四氯化碳浓度C的对数值ln[C（/μg·L-1）]与时间t呈良好的线性关系,相关系数均在0.95以上。通风速率为40mL·min-1的土柱A各取样口四氯化碳去除反应速率常数k值在0.0132～0.0155h-1之间,通风速率为70mL·min-1的土柱B各取样口k值在0.0178～0.0222h-1之间,说明增大通风速率能提高土壤中四氯化碳污染物的去除效率。     

地下水位波动对包气带中氮素运移影响规律的研究

为探讨地下水位不同尺度波动幅度中氮素运移规律,室内通过土柱I、Ⅱ和Ⅲ模拟地下水位的不同尺度上下波动进行对比试验。试验中柱I水位保持静止、柱Ⅱ波动幅度为15em、柱Ⅲ波动幅度为30cm,在实验装置相同情况下,得出三柱各土层中DO、NO3^- —N和NH4^＋ -N浓度变化。结果表明：柱I中DO、NO3^- -N和NH4＋^ —N变化较小,而柱Ⅱ、Ⅲ中DO、NO3^- —N和NH4^＋ —N均变化较显著,且柱Ⅲ的变化幅度要大于柱Ⅱ。对比水位静止的柱I,当水位上升和下降后,柱Ⅱ、Ⅲ各土层中DO和N0i—N浓度均减小和增大,增减趋势相同,但DO和NO3^- —N的变化幅度均为柱III〉柱II;NH4^＋ —N浓度相应地增大和减小,增减趋势相同,但幅度柱Ⅲ〉柱Ⅱ。柱Ⅱ、Ⅲ进行两次循环波动后,两土柱各土层中NH4^＋ -N均减小,且减小幅度柱Ⅲ〉柱Ⅱ;NO3^- -N无明显规律。可知,水位波动对土层中硝酸盐运移影响显著,且水位波动尺度与该影响程度相关,故在地下水硝酸盐污染风险评价时,不可忽视水位波动对氮素运移的影响。     

天然磁铁矿和商用Fe3O4修复Hg(II)污染地下水的模拟研究

目前汞污染地下水修复面临很大的技术和成本挑战,亟需发展修复效果好、经济效益性高的汞污染地下水修复技术和修复材料。通过批量实验和光谱分析探究了天然磁铁矿和商用Fe_3O_4对Hg(Ⅱ)的去除效率和去除机制,并分析了两种材料对模拟地下水中Hg(Ⅱ)的吸附和脱附行为。结果表明,天然磁铁矿和商用Fe_3O_4对Hg(Ⅱ)的去除受pH、Hg(Ⅱ)初始浓度、Cl-等因素的影响;二者对Hg(Ⅱ)的去除均符合准二级动力学模型和Freundlich模型;天然磁铁矿对Hg(Ⅱ)的去除机制主要是羟基络合与物理吸附,而商用Fe_3O_4对Hg(Ⅱ)的去除主要是化学还原与物理吸附。二者对模拟地下水中Hg(Ⅱ)的去除率分别达90%和95%,具有修复Hg(Ⅱ)污染地下水的应用潜力。     

牡蛎壳作生物滞留填料对城市地表径流污染物去除效果研究

选择磷吸附性能最强的牡蛎壳作为填料,在实验室构建3个生物滞留模拟装置(A柱:养殖牡蛎壳;B柱:海滩牡蛎壳;C柱:养殖牡蛎壳存在淹没区),采用道路径流模拟配水作为进水,研究牡蛎壳作为填料对青岛市城市径流常见污染物氮磷及COD的处理效果,并对各污染物去除机理进行探讨。结果表明:3种牡蛎壳填料的生物滞留设施对总磷的去除效果最好,在进水磷浓度为0.57～1.83 mg/L条件下,无淹没区装置平均去除率为96.12%,存在淹没区的装置平均去除率为91.02%。养殖牡蛎壳与海滩牡蛎壳对磷的去除效果并无明显差异,淹没区不利于磷的去除。在前期进水过程中(前5次进水)3个模拟装置氨氮(NH_4~+)的出水浓度高于进水浓度,延长落干期后,装置的NH_4~+去除率均上升,B柱NH_4~+平均去除率(58.83%)相对于A柱(48.77%)及C柱(53.06%)更高,有无淹没区对NH_4~+去除并无明显影响。由于填料中有机物的渗沥,首次进水出现严重COD淋出,在随后的进水过程中,COD去除效果迅速上升并稳定,3个模拟柱去除率分别为50.34%,23.47%和47.75%。由于反硝化作用受阻,对硝氮(NO_3~-)的去除效果不佳。整体看来,养殖牡蛎壳可以应用于青岛市生物滞留设施的填料,为加强滞留设施NO_3~-的去除效果,还需要采用强化脱氮措施。     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

Effect of some fungicide seed treatments on the survival of Bradyrhizobium japonicum and on the nodulation and yield of soybean [Glycine max. (L) Merr.]

Several commercial fungicide seed treatments were evaluated for their possible effect on the survival of Bradyrhizobium japonicum on seeds and on the nodulation and yield of soybeans in a greenhouse and a field experiment. quinolate Pro (carbendazim and oxine copper), Vitavax 200FF (carboxin and thiram), and Monceren (pencycuron) had a small effect or no effect on the survival of B. japonicum and on the nodulation and yield of soybeans. They can thus be considered compatible with soybean seed inoculation. Germipro UFB (carbendazim and iprodione), Apron 35J (metalaxyl), and Tachigaren (hymexazol) decreased B. japonicum survival and the nodulation and yield of soybeans and thus cannot be considered compatible with soybean seed inoculation.     

Einfluss der düngungsmethoden auf die entwicklung von zuckerrübenkrankheiten

Während neunjähriger (1994-2002) Untersuchungen in der Versuchsanstalt Ba?cyny (Fahlerde, Fall-Gleyboden, ausgebildet aus leichtem Lehmboden) wurde der Befall mit Krankheiten an der Zuckerrübe in Abhängigkeit von der Düngungsmethode bewertet. Folgende Methoden wurden angewendet: A - Mineraldünger, B - Stalldung und Mineraldünger, C - Stroh-, Gründung und Mineraldünger, D - Kompostdünger und Biopräparate (ökologische Düngung). Auf den Objekten A, B, C wurden bei konstanter Phosphor-Kalium-Düngung die Stickstoffgaben von 0 bis 180 kg.ha^?1 differenziert. Auf dem ökologischen Objekt D ohne Mineraldünger wurden statt Stickstoff die Biopräparate P₅₀₀ und P₅₀₁ verabreicht. Der geringste Befall von Krankheiten wurde an der Zuckerrübe auf jenem Objekt festgestellt, das mit Kompost und den Biopräparaten gedüngt worden war. Im Rahmen der konventionellen Düngungsmethoden wurde allgemein die höchste Intensität der Krankheiten an der mit Stroh, Gründung und Mineraldünger gedüngten Zuckerrübe beobachtet. Ausnahmen von dieser Regel bildete das Vorkommen von echtem Mehltau und Keimlingsfäule. Auf den Objekten A, B, C nahm die Intensität der Krankheiten mit der Steigerung der Stickstoffgabe zu. Auch die auf Objekt D verabreichten Biopräparate stimulierten die Entwicklung der Krankheiten. The effect of various fertilization methods on the diseases of sugar beet was estimated on the basis of nine-year studies (1994-2002) conducted in the Experimental Production Farm in Ba?cyny on loess-based, sedimentary-gley, light-clay soil. The following fertilization methods were applied: A - mineral fertilization, B - mineral and manure fertilization, C - straw, green manure and mineral fertilization, D - ecological compost and biodynamic preparations fertilization. In the objects A, B and C fertilized with phosphorus and potassium, various doses of nitrogen ranging from 0 to 180 kg/ha^?1 were used. In the ecological object D, where mineral fertilization was not used, biodynamic preparations P₅₀₀ and P₅₀₁ were applied instead of nitrogen. The lowest ratio of the diseases of sugar beet was observed in the object fertilized with the compost and biodynamic preparations. In view of the conventional fertilization methods, generally the highest incidence of diseases was noted in the sugar beet fertilized with straw, green manure and mineral fertilizers. The exception was the occurrence of powdery mildew and the black leg. In objects A, B and C the incidence of the diseases increased with the increase in nitrogen doses. The applied biodynamical preparations in the object D stimulated the development of diseases too.     

Prospects for control of Pythium damping-off of lettuce with Trichoderma,Gliocladium and Enterobacter spp.

Summary Damping-off of lettuce (Lactuca sativa) caused by Pythium ultimum was studied in pots containing a non-sterile potting mix in the glasshouse. Fifty P. ultimum sporangia g^-1 compost reduced the plant stand to 15% and shoot dry weight to 18%, but this reduction was totally prevented by applying Trichoderma harzianum at 2×10⁵ viable propagules g^-1 potting mix. Gliocladium virens and Enterobacter cloacae also alleviated the damping-off. E. cloacae did not adversely affect the action of the fungal antagonists. The co-existence of the bacterial and fungal antagonists was revealed on the root surface and inner surface of the testa by scanning electron microscopy, indicating the compatibility of the biocontrol agents.     

细菌、真菌及植物氮营养信号研究进展

氮素吸收代谢是所有生物生命活动的核心部分,因此,各种生物对氮的吸收与同化过程都有精细的调节。这种调节依赖于生物对体内氮素状况信号及体外（生长介质中）氮素信号的感受。过去几十年中,在细菌、真菌中已经对氮素营养信号有了较好的研究,而植物中则相对缓慢,但也有了一定的认识。本文重点比较细菌、真菌及植物中氮信号系统的组成,以期为进一步认识植物中的氮信号接受与转导系统提供启示。     

Aircraft operations near concentrations of birds in Antarctica: The development of practical guidelines

Aircraft operations have the potential to disturb and to impact negatively on bird life. A gradient of increasing behavioural response is evident in birds when exposed to increasing aircraft stimulus. The most major disturbance is likely to lead to impacts on the health, breeding performance and survival of individual birds, and perhaps bird colonies. A process of revision to policies on aircraft operations contained in management plans for a number of specially protected areas in Antarctica by the United Kingdom, accompanied by consultations made within the scientific community through the Scientific Committee on Antarctic Research (SCAR) and with operational interests through the Council of Managers of National Antarctic Programmes (COMNAP) resulted in new guidelines being adopted by the Antarctic Treaty Consultative Parties in June 2004. The principal recommendations of the guidelines are that bird colonies should not be overflown below 2000 ft (∼610 m) above ground level and landings within 1/2 nautical mile (∼930 m) of bird colonies should be avoided wherever possible. These guidelines are less stringent and less specific than those that were recommended by the SCAR specialist group on birds, and represent a compromise to accommodate operational needs. While the adoption of clear and consistent guidelines for the operation of aircraft in Antarctica is welcome in that this provides practical advice that is likely to reduce incidences of close aircraft/bird encounters, there remains insufficient knowledge of the interactions between aircraft and birds in Antarctica, and the consequent impacts on individual birds and on bird populations. It is important, therefore, that the guidelines adopted are considered interim, and should be kept under scrutiny with revisions made as new and improved research results appear.     

The abundance of heterocystous blue-green algae in rice soils and inocula used for application in rice fields

Summary Algal populations were quantified (as colony-forming units [CFU] per square centimetre) in 102 samples of rice soils from the Philippines, India, Malaysia and Portugal, and in 22 samples of soil-based inocula from four countries. Heterocystous blue-green algae (BGA) were present in all samples. Nostoc was the dominant genus in most samples, followed by Anabaena and Calothrix. In soils, heterocystous BGA occurred at densities ranging from 1.0 × 10² to 8.0 × 10⁶ CFU/cm² (median 6.4 × 10⁴) and comprised, on average, 9% of the total CFU of algae. Their abundance was positively correlated with the pH and the available P content of the soils. In soil-based inocula, heterocystous BGA occurred at densities ranging from 4.6 × 10⁴ to 2.8 × 10⁷ CFU/g dw (dry weight), comprising only a moderate fraction (average 13%) of the total algae. In most soils, the density of indigenous N₂-fixing BGA was usually higher than that attained by applying recommended rates of soil-based inoculum. Whereas research on the practical utilization of BGA has been mostly directed towards inoculation with foreign strains, our results suggest that attention should also be given to agricultural practices that enhance the growth of indigenous strains already adapted to local environmental conditions.Maître de Recherches ORSTOM (France), Visiting Scientist at IRRI