岩层倾向对喀斯特槽谷区地表/地下产流过程的影响

喀斯特槽谷区在降雨过程中极易发生水土流失,这使得该区生态环境被破坏。以喀斯特槽谷区为研究对象,通过室内模拟其典型顺/逆层坡面特征及地下孔裂隙发育程度,利用人工降雨试验研究不同雨强条件下地表地下产流特征,从而揭示喀斯特槽谷区地表地下产流机制。结果表明:(1)喀斯特槽谷区地表地下产流受雨强影响,小雨强(30 mm/h)条件下地下产流量大于地表产流量,中雨强(60 mm/h)条件下地表产流量增大且裸坡条件下地表产流量大于地下产流量,大雨强(90 mm/h)条件下裸坡与顺层坡的地表产流量均大于地下产流量。(2)地下孔裂隙发育程度对地表地下产流量的分配比例产生影响,地下孔裂隙度越大则地下产流量越多,且2%～3%的地下孔裂隙度时地表地下产流量分配比例发生转变。(3)不同岩层倾向条件下,地表产流量及其分配比例最高为裸坡,最低为逆层坡,地下产流量及其分配比例最高为逆层坡,最低为裸坡。(4)不同岩层倾角条件下,顺层坡地表产流量最高为30°,最低为90°,地下产流量则相反;逆层坡地表产流量最高为90°,最低为60°,地下产流量最高为60°,最低为90°。研究结果可为喀斯特槽谷区地表及地下产流机制的进一步认识提供科学依据。     

喀斯特槽谷区岩石与坡面夹角对坡面集中流水力学特性的影响

喀斯特槽谷区地表出露的岩石与坡面形成不同夹角,塑造了复杂的微地貌,显著改变坡面集中水流路径,使得水流特性发生重大变化。目前,不同岩石与坡面夹角下集中流水力学特性的变化特征还不清楚。通过室内放水冲刷模拟试验,研究了3个坡度(10°、15°和20°)、3个冲刷流量(5、7.5、10 L·min-1)和6个岩石与坡面夹角(30°、60°、90°、120°、150°和180°(0°))组合条件下喀斯特槽谷区地表集中流的水力学特性。结果表明:集中水流雷诺数(Re)随冲刷历时变化趋势较复杂,试验条件下,Re随流量的增大而增大,随坡度变化规律不明显,变化范围为517～3343。Darcy-Weisbach阻力系数(f)随冲刷历时表现出增大的变化趋势,其随坡度增大而增大,随流量增大而减小,变化范围为0.62～5.70。Re和岩石与坡面夹角关系均不显著,f和岩石与坡面夹角间的关系在各流量和坡度组合下表现不同。f与Re之间的耦合关系受岩石与坡面夹角的显著影响,当岩石与坡面夹角小于90°时,f-Re关系用对数方程描述比较好;夹角大于等于90°时,则用幂函数方程描述更好。试验条件下,当Re1 791时,f与Re关系不显著;当Re1 791时,f与Re则呈显著正相关。本研究可为喀斯特槽谷区土壤侵蚀预报模型的建立提供依据。     

草地坡面水动力学特性及其阻延地表径流机制研究

利用野外实地放水试验,分析草地减流减沙效益,研究草地与裸地坡面的产流产沙过程与坡面流水动力学特性。试验结果表明,草地与裸地坡面土壤入渗过程均符合Horton入渗公式,且裸地坡面土壤入渗率约为草地的45%;草地坡面含沙率平均值较裸地减少70%左右、输沙率减少80%左右、径流系数减少30%左右;裸地与草地坡面流雷诺数Re均属于层流范畴,当坡面径流量较小时,裸地和草地坡面流的雷诺数和弗劳德数属于层流中的缓流范畴,当坡面径流量进一步增大,裸地坡面径流属于过渡流急流流态;草地和裸地坡面径流深没有明显差异,草地坡面径流流速明显较裸地低,而且Darcy-weisbach阻力系数f和曼宁糙率系数n的平均值分别是裸地的3.4和2倍。     

喀斯特槽谷区岩层倾向对土壤入渗特性的影响

为了解岩层倾向对喀斯特槽谷区土壤入渗特性的影响,以重庆市青木关岩溶槽谷区顺/逆层坡为研究对象,分析5种典型土地利用方式裸地(AL)、辣椒地(PL)、玉米地(CL)、林地(FL)、草地(GL)在顺/逆层坡的土壤入渗能力差异,并探讨土壤物理性质对土壤入渗能力的影响。结果表明:(1)＞0.25 mm水稳性团聚体含量、毛管持水量、黏粒以及粉粒含量在顺/逆层坡存在显著差异(p<0.05),其中在>0.25 mm水稳性团聚体含量和毛管持水量方面,分别为PL与FL的顺/逆层坡差异最大,在黏粒和粉粒方面,CL的顺/逆层坡差异最大,且均为逆层坡＞顺层坡。(2)除FL顺层坡的土壤渗透能力低于逆层坡外,其余4种土地利用方式下的土壤入渗能力均表现为顺层坡高于逆层坡。(3)土壤渗透特性在顺/逆层坡均与容重呈极显著负相关关系(p<0.01),在顺层坡与总孔隙度、非毛管孔隙度、＞5 mm水稳性团聚体含量和饱和持水量呈极显著正相关关系(p<0.01),在逆层坡与非毛管孔隙度、饱和持水量、粉粒含量呈极显著正相关关系(p<0.01);通过多元逐步回归分析与通径分析发现,顺/逆层坡土壤入渗能力的首要决策因素均为容重,其次分别为>5 mm水稳性团聚体含量和粉粒含量。(4)对比4种土壤入渗过程的拟合模型,Philip模型对顺/逆层坡的土壤入渗过程拟合效果最佳。研究结果可为喀斯特槽谷区不同岩层倾向的水土流失防治以及植被恢复提供数据支撑。     

喀斯特槽谷区坡面集中水流曼宁系数变化特征

[目的]探究喀斯特槽谷区不同岩石与坡面夹角影响下地表集中水流阻力变化特征,为该区土壤侵蚀模型构建提供科学依据。[方法]在3个坡度(10°,15°,20°),3个冲刷流量(5,7.5,10 L/min)和6个岩石与坡面夹角角度(30°,60°,90°,120°,150°,180°)组合条件下开展室内放水冲刷试验,研究喀斯特槽谷区不同岩石与坡面夹角下地表集中水流曼宁系数的变化规律及其影响因素。[结果](1)地表集中水流曼宁系数n随冲刷历时呈迅速增大再缓慢增长或趋于稳定的变化趋势。不同夹角的n值大小顺序为:n_(180°)n_(150°)n_(90°)n_(30°)n_(120°)n_(60°)。(2)当岩石与坡面夹角大于30°时,n与水深h显著相关,夹角为30°时,二者关系不显著;试验条件下,n与雷诺数Re关系不显著,与弗汝德数Fr呈显著幂函数负相关。(3)相对水深曼宁系数n/h随夹角增大呈先增后减的变化趋势。(4)岩石与坡面夹角大于30°时,n/h与Re均呈幂函数负相关,夹角为30°时,二者关系不显著;不同岩石与坡面夹角的n/h与Fr关系均不显著。[结论]喀斯特槽谷区坡面集中水流曼宁系数n受岩石与坡面夹角的显著影响,随夹角增大总体呈先减后增的趋势。     

陡坡面发育的细沟水动力学特性室内试验研究

为了为黄土高原陡坡水蚀预报模型的建立提供科学依据,通过组合不同坡度(21°、24°、27°)、不同流量(6.5、8.5、10.5 L/min)的陡坡室内放水冲刷试验,对坡面细沟侵蚀发生过程中的坡面流水动力学特性进行了研究.结果表明,在试验的坡度和流量范围内,坡面流的雷诺数Re在798～4620之间变化,且雷诺数Re变化幅度随冲刷历时的增大而增大.而坡面流弗劳德数Fr在整个试验过程中均大于1,表明坡面流处于急流范围.坡面流阻力系数f随雷诺数Re的增大而增大,其变化还受坡度的影响.坡面在径流冲刷侵蚀过程中,流速随冲刷时间的延长和冲刷形态的变化呈现出先减小后增大义减小的变化趋势.     

砒砂岩陡坡面径流水动力学特征

为研究砒砂岩地区陡坡面径流的侵蚀规律,为该地区坡面水蚀预报模型的建立提供科学的理论依据,通过室内模拟冲刷试验,对不同冲刷流量和坡度的坡面径流水动力学特征进行研究。结果表明:在试验的冲刷流量和坡度范围内,砒砂岩坡面径流流速随冲刷流量和坡度的增大而增大,它们之间呈幂函数关系。径流雷诺数(Re)随随冲刷流量的增大而增大,40°则是Re变化的临界坡度,此时Re最大,而弗罗德数(Fr)的变化趋势正好相反。当冲刷流量大于4L/min时,径流流态为紊流和急流,其余处理坡面径流流态都为层流和急流。径流Darcy-Weisbach阻力系数(f)随压实度增大而减小,随冲刷流量的增大而增大,60°则是f变化的临界坡度,此时f最大,且f和输沙率有一定的正相关关系。     

含沙量对高陡边坡径流水动力学特性的影响

[目的]揭示含沙量对高陡边坡水动力学特性的影响,为高陡边坡土壤侵蚀机理模型精度的提升提供理论支撑。[方法]设定3个含沙梯度(0,4%,8%)和3个放水梯度(12,16,20 L/min),在36°坡面进行野外径流冲刷试验。[结果]随着放水流量的增大,平均流速随着含沙量增加而减小的趋势较小,雷诺数Re随着含沙量增加而减小的趋势较明显;当放水流量为16,20 L/min时,随着含沙量的增加,坡面流态均由紊流向过渡流发展;弗汝德数Fr随着含沙量的增加而增大,且均大于1,坡面径流流态属于急流。阻力系数f与雷诺数Re呈极显著幂函数关系(p<0.01),随着含沙量的增加,雷诺数Re对阻力系数f的影响逐渐减弱。含沙量与平均流速、雷诺数、阻力系数、水流剪切力和水流功率呈极显著负相关关系(p<0.01),相关系数绝对值大小顺序为R(Re)>R(ω)>R(τ)>R(ν)>R(f),雷诺数Re是描述水动力学参数与含沙量关系的最佳参数,含沙量与弗汝德数Fr关系不显著,与雷诺数、水流功率、水流剪切力以及流速间的关系可用二元线性函数表示。[结论]含沙量对高陡边坡水动力学特性具有...     

岩土覆被格局对西南喀斯特坡地产流产沙的影响

为研究不同岩土格局对喀斯特坡地水土流失/漏失的影响,利用人工模拟降雨试验,以裸坡为对照组,研究镶嵌格局、横坡格局、顺坡格局3种岩土覆被格局下的坡面产流产沙特征。结果表明：(1)顺坡格局的地表产流量最多,分别较镶嵌格局、横坡格局与裸坡的地表产流量增加88.6%,67.1%,576.1%,同时顺坡格局的地下产流量最少,分别较镶嵌格局、横坡格局与裸坡减少37.5%,36.1%,39.2%。(2)地表产沙量顺坡格局>镶嵌格局>横坡格局>裸坡,地下产沙量镶嵌格局>横坡格局>顺坡格局>裸坡。3种岩土格局的地表产沙量较裸坡均有明显增加,但地下产沙量相对增加较少。(3)岩土格局可改变地表径流泥沙关系,地表累积径流量与地表累积产沙量呈幂函数关系,镶嵌格局明显改变地表径流泥沙关系,使坡面地表侵蚀量显著提升。研究结果可进一步深化对喀斯特坡地降雨侵蚀规律的认识,为喀斯特地区的石漠化治理提供参考依据。     

草被覆盖下坡面径流入渗过程及水力学参数特征试验研究

利用人工模拟降雨试验,定量研究了在90 mm/h降雨强度下20°陡坡面不同被覆条件下(80%,60%,40%,20%)苜蓿草地的产流产沙入渗变化规律.分析了草地侵蚀产沙的水力学参数特征.试验结果表明,不同草被覆盖条件下草地累积径流量和累积产沙量与降雨时间呈显著的幂函数关系,随着草地覆盖度的减小而增大.随着草被覆盖度的增加,坡面径流量呈减小的趋势,草地人渗率呈增加的趋势,草被坡面径流量和入渗率呈明显负线性相关.分析了不同草被覆盖条件下草地的坡面水流平均流速、水力半径、雷诺数、弗罗德数和阻力系数特征,从水力学角度揭示了不同覆盖度草地的拦沙效应.     

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