地面覆盖条件下雨强和坡度对红黏土坡面侵蚀过程的影响

为揭示地面覆盖条件下第四纪红黏土坡面在不同雨强和坡度时的侵蚀变化规律,选取3个降雨强度(1.0,1.5,2.0 mm/min)和3个坡度(10°,15°,20°),通过人工模拟降雨试验,分析坡面产流、产沙、入渗特征,并以15°为例计算覆盖坡面的减流减沙效益。结果表明:(1)坡面产流时间随雨强和坡度增加而提前,覆盖对产流时间有明显的滞后作用,雨强的增加会削弱覆盖延缓产流的作用;坡面径流率呈现前期增长,后期趋于稳定的变化特征;(2)当坡度一定,雨强从1.0 mm/min增加至2.0 mm/min,累积侵蚀量增加1.89～2.96倍;雨强一定,坡度从10°增加至20°,累积侵蚀量增加1.91～3.45倍;(3)坡面初始入渗率和入渗总量随坡度的增加而减小,而雨强的增大会增加坡面初始入渗率,减少入渗总量;(4)15°条件下覆盖坡面的径流量和泥沙量较裸坡平均减少50.26%和95.31%,松针覆盖的水土保持效益显著,且减沙效应大于减流效应;(5)坡度对覆盖坡面累积产流量和累积产沙量的影响程度大于雨强,不同雨强、坡度下累积径流量与累积产沙量呈现幂函数关系(R~20.97)。研究结果可为南方红壤丘陵区林下水土流失治理与生态恢复提供参考。     

采石场松散体坡面两种治理措施的水土保持效益

通过修建径流小区,对北京市房山区黄院采石场的治理进行了连续两年的坡面径流观测,用对比分析的方法研究了采石场治理初期不同年份内不同治理措施的水土保持效益。结果表明,在采石场治理初期,不同的坡度、不同的治理措施、不同的植被覆盖度均对坡面水土流失的影响有较大差异。当坡度为25°时,铺设生态袋措施能够有效防治水土流失;当植被覆盖度小于15%时,影响水土流失的主要因素为松散体坡面的孔隙度;当植被覆盖度大于60%时,影响水土流失的主要因素是降雨量和降雨强度。     

东北黑土区野外模拟降雨条件下产流产沙研究

对不同坡度(3°,5°,7°,9°,12°,15°)的径流小区,采用野外人工模拟降雨试验方法,对不同降雨强度(1.24,1.87,2.17 mm/min)黑土坡地产流和产沙随雨强和时间的变化特性进行模拟试验.通过对模拟降雨试验数据分析,得出结论:①同一坡度下,产流时间随雨强的变化具有明显的规律性,雨强越大,产流所需的时间越短.②累计产沙量随累计径流量的增加呈幂函数增加,满足y=AxB函数形式(定义A为产沙基数系数,B为产沙速率系数).③侵蚀产沙量随含沙量的增加呈线性增加,其表达式满足y=ax+b形式,系数a体现了产沙能力.④随着雨强的增大坡面径流量也增大;随着坡度的增大坡面径流量呈现先减小后增加,最后减小的趋势.⑤随着雨强的增大,坡面侵蚀产沙量基本呈现增加的趋势;而随着坡度的增加,坡面侵蚀产沙量变化复杂,12°～l5°之间存在试验条件下的临界坡度.     

模拟降雨条件下第四纪红黏土坡面侵蚀过程

通过室内模拟降雨试验,分析雨强和坡度对第四纪红黏土坡面侵蚀过程的影响,揭示南方红壤低山丘陵区第四纪红黏土坡面侵蚀机理。根据研究区地形和降雨特点,设计坡度10°,15°,20°,雨强1.0,1.5,2.0mm/min,研究两者对坡面侵蚀过程的影响。结果表明:(1)坡面初始产流时间随着坡度和雨强的增大而逐渐减小;同一雨强下,径流系数大小为20°15°10°。(2)不同试验处理条件下,坡度由10°增加到20°,坡面累积产沙量增加0.46~1.98倍;降雨强度由1.0mm/min增加到2.0mm/min,坡面累积产沙量增加1.37~3.85倍。(3)1.0,1.5mm/min雨强条件下,坡面侵蚀泥沙以0.25mm水稳性团聚体占优,2.0mm/min雨强条件下,坡面侵蚀泥沙0.25mm水稳性团聚体为主。(4)坡度与雨强对坡面径流系数、侵蚀率和累积产沙量影响极显著(P0.01),坡面累积径流量和累积产沙量构成幂函数模型。研究结果为揭示坡度与雨强对第四纪红黏土坡面侵蚀过程的作用机理提供参考。     

黄河下游河岸坡面产流产沙特征及其与汇流路径长度关系

植被和地形是影响坡面侵蚀过程的重要因子,探讨两者交互作用下坡面产流产沙和汇流特征对深入理解坡面侵蚀过程和水土保持具有重要意义。采用模拟降雨试验,探讨不同降雨强度(54和90 mm·h~(-1))、坡度(5°、10°、15°、20°)和植被盖度(0%、15%、30%)下黄河下游河岸坡面的侵蚀产流、产沙特征,并基于水文连通性模型——汇流路径长度指数(Flowlength)探究植被和地形在土壤侵蚀过程中的作用以及汇流长度与产流产沙特征的关系。结果表明:54和90 mm·h~(-1)雨强下,不同植被盖度对径流流速均有减缓作用,而90 mm·h~(-1)雨强下30%盖度的减缓作用较为明显;径流总量和径流深随坡度和植被盖度增加而逐渐减少的变化基本一致,随雨强增加,受坡度影响逐渐增大。54 mm·h~(-1)雨强下,当坡度15°时,侵蚀产沙量随坡度增加增幅较小;当坡度15°后,侵蚀产沙量增幅较大。90mm·h~(-1)雨强下,当坡度15°时,侵蚀产沙量随坡度增加而增加;当坡度15°后,其随坡度增加而减少。相关分析表明,坡度对产沙量、产流量和径流深均具有显著影响,显著水平分别为P 0.001、P 0.01和P 0.05;植被盖度仅对平均流速影响显著(P 0.05)。但植被盖度对汇流路径长度影响极为显著(P 0.001),裸坡的汇流路径长度明显大于植被覆盖坡面;坡面产流产沙量随汇流路径长度的增加基本呈增加趋势。在坡度和植被盖度交互作用下,坡面产流所引发的土壤侵蚀效应受坡度影响较为明显,而在汇流过程所引发的土壤侵蚀效应中,植被的影响明显大于坡度。     

黄土坡耕地径流水力学参数与侵蚀产沙的模拟

为了明确连续降雨条件下黄土坡耕地微地形的径流产沙及水力学特征,基于4种坡度(5°,10°,15°,25°)、4种耕作方式(直线坡、人工锄耕、人工掏挖、等高耕作)和2种雨强(60mm/h,120mm/h)的组合,通过室内模拟连续90min降雨试验,对不同坡面的径流泥沙特征和水力学参数进行了定量分析和计算。结果表明:4种耕作措施的径流量和产沙量均遵循一致的规律,从大到小均为直线坡人工锄耕人工掏挖等高耕作,直线坡的径流量和产沙量分别是等高耕作坡面的2倍和2.3倍,其水土保持效应依次增强;相同耕作方式下,与60mm/h雨强相比,120mm/h雨强下的径流量由1.04kg/min增大到3.02kg/min,雨强对径流量的影响显著;径流量和泥沙量随时间均呈现对数变化趋势;相同降雨历时下,坡面流随雨强和坡度的增大,从层流和缓流向紊流和急流发展,加剧了水土流失。耕作方式、雨强和坡度是影响黄土坡耕地侵蚀产沙过程及水力学特征的重要因素。因此,通过实施有效的保护性耕作、削弱坡度效应将有助于黄土坡耕地的水土保持。     

砾石覆盖条件下盐碱土边坡降雨侵蚀水动力学特征

为了探究砾石覆盖对盐碱土坡面侵蚀的减沙效应,通过室内模拟降雨试验,研究不同坡度和雨强条件下降雨径流水动力学特征及产沙受砾石覆盖的影响。试验坡度选取15°和30°,雨强选取92,119mm/h,坡面砾石覆盖度分别为0,10%,20%,40%,60%,80%,采用染色示踪法测定坡面径流流速。结果表明:不同坡度和雨强条件下,水流产沙率随坡面砾石覆盖度增大先增后减;雷诺数与弗劳德数均随砾石覆盖度增大呈先增后减的抛物线趋势,曼宁糙率、Dracy-Weisbach阻力系数、坡面径流剪切力和径流功率均与坡面砾石覆盖度呈线性正相关;径流功率预测产沙率效果较好,二者呈对数关系(R2=0.47)。     

坡度对农业耕作措施水土保持作用的影响

农业耕作措施是水土保持三大措施之一,在坡耕地水土保持中起关键作用。利用人工模拟降雨试验方法,对不同坡度条件下农业耕作措施水土保持作用进行了研究。农业耕作措施包括等高耕作、人工掏挖和人工锄耕,以平整坡面为对照措施;降雨试验在长4m,宽1m的径流小区完成;坡度为5°,10°,15°,20°,25°;降雨强度为1,1.5,2mm/min。结果表明:与平整坡面相比,等高耕作、人工掏挖和人工锄耕分别减小产流量38.19%,32.25%和15.84%;减小产沙量均在50%以上,说明农业耕作措施具有明显的水土保持作用。通过对坡度与产流量、产沙量关系分析表明,在耕作坡面,坡度会影响产流量,但是大坡度与小坡度之间差异不显著。相反,坡度对产沙量具有显著影响,在小坡度条件下,产沙量受坡度的影响较小。当坡度大于15°后,坡度每增加1°,等高耕作、人工掏挖和人工锄耕耕作措施保土作用平均降低3.08%,4.74%和7.61%。回归分析表明产沙量与坡度之间存在指数函数关系。可见,坡度对农业耕作措施保水作用和保土作用的影响不同。     

不同雨强和坡度下侵蚀性风化花岗岩母质坡地产流产沙特征

为研究解决南方侵蚀性风化花岗岩地区的水土流失问题,该文采用室内人工模拟降雨方法研究了不同降雨强度(30,60,90,120,150 mm/h)和不同坡度(5°,8°,15°,25°)条件下的风化花岗岩残积坡地的土壤侵蚀过程。结果表明:1)坡面径流的初始产流产沙时间都随着坡度和雨强的增大而提前;2)坡面径流量与坡度之间不呈简单的正相关关系,径流系数随雨强的变化呈现指数相关关系,入渗率在雨强为30~120 mm/h之间在坡度8°左右出现极大值;3)侵蚀产沙量随坡度和雨强的增大而增大,其与坡度之间的关系可以用幂函数表示,决定系数均达到0.815,与雨强之间为指数函数关系,决定系数均达到0.889以上;4)水力侵蚀对泥沙具有分选性,径流侵蚀挟带泥沙中的粉粒、黏粒以及细砂粒含量较多;5)坡度和雨强对于侵蚀产沙量的综合影响可以用线性相关方程来比较准确地描述,对产沙量的影响权重排序为:含沙量雨强径流系数坡度。     

雨强和坡度对嵌套砾石红壤坡面产流产沙的影响

采用人工模拟降雨的方法研究了嵌套砾石红壤坡面的产流产沙特征,分析了雨强(60,120mm/h)和坡度(10°,15°,20°,25°)条件下嵌套砾石和无砾石红壤坡面的产流和产沙过程差异。结果表明:(1)产流开始时间T_(嵌套砾石)T_(无砾石),60mm/h雨强条件下嵌套砾石较无砾石坡面在10°,15°,20°,25°坡度分别延迟4.20,2.95,2.23,1.03min;(2)坡度相同时,嵌套砾石坡面较无砾石坡面产流率明显减少,但雨强的增大会掩盖嵌套砾石对坡面产流率减小的影响;(3)嵌套砾石红壤坡面在60mm/h雨强、坡度10°条件下平均产流率最小,在120mm/h雨强、25°坡面下平均产流率是前者的4.5倍;无砾石红壤坡面在120mm/h雨强、坡度25°条件下平均产流率最大,为最小平均产流率的4.8倍;(4)各坡面产沙强度、次降雨产沙量随雨强和坡度增大而增大,60mm/h雨强、坡度10°和25°时,嵌套砾石坡面平均产沙强度为无砾石坡面的6.0%和28.4%;120mm/h雨强时,此两个坡度的嵌套砾石坡面为无砾石坡面平均产沙强度的33.9%和25.3%。     

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