秸秆还田对中国农田土壤固碳效应影响的研究

采用Meta分析法定量研究了秸秆还田对中国农田土壤有机碳(SOC)含量的影响及影响因素。结果表明：秸秆还田比不还田可显著增加SOC含量，但随土壤深度加大，SOC的增加效果呈现下降趋势。同时，秸秆还田土壤的固碳速率随还田年限的增加而显著减小(P<0.01)，秸秆还田3～5、6～9a及≥10a土壤的固碳速率分别为0.58、0.19和0.09g/(kg·a)。此外，在施氮量100～400 kg/hm²、年均温度≥13℃、年均降水量≥800 mm和初始土壤C/N≥10条件下，0～20 cm土层的固碳作用表现较佳，而超过20 cm深度的土壤固碳作用受上述因素影响效果不显著。     

松嫩平原秸秆还田对连作春玉米氮素供应与吸收的影响

为探明松嫩平原秸秆还田对连作春玉米氮素供应与吸收的影响,在松嫩平原中南部,采用框栽和¹⁵N同位素标记的方法,设置5个秸秆还田量,分别为0(CK)、9.20、18.40、27.60和36.80 t·hm^-2,均施入¹⁵N标记的尿素350 kg·hm^-2(纯氮量约160 kg·hm^-2),开展秸秆还田试验。结果表明,秸秆还田改变了春玉米对肥料氮和土壤氮的利用比例,在一定秸秆还田量条件下,随着秸秆还田量的增加,苗期春玉米植株氮素积累中肥料氮所占比例增加,而拔节期后则呈相反趋势。通过方程拟合可知,秸秆还田量低于12.49 t·hm^-2时可以较CK提高当季氮肥利用率,高于12.49 t·hm^-2时则低于CK。秸秆还田不利于春玉米苗期和拔节期生长;秸秆还田量为11.25 t·hm^-2时,最有利于春玉米产量的形成,秸秆还田量高于23.96 t·hm^-2时则会引起减产。综上,在松嫩平原中南部,配施尿素350 kg·hm^-2时,最适秸秆还田量为11.25 t·hm^-2。本试验较系统地研究了玉米不同秸秆还田量对土壤供氮和下茬玉米氮素吸收的影响,为科学解析秸秆还田与土壤供氮关系提供了依据。     

不同碳源对植烟土壤碳平衡的影响

为探索不同碳源对土壤碳的提升作用,开展了不同碳源对烤烟生长季土壤碳平衡影响的研究,旨在为植烟土壤有机肥施用调控提供理论依据。试验设在四川省攀枝花市,以烤烟为供试作物进行田间小区试验。设对照(不施有机肥)、秸秆、农家肥、油枯、农家肥+油枯5个不同施肥处理,3次重复。采用VaisalaMI70土壤呼吸测量系统进行田间监测,并同时观测环境条件。对烤烟根系进行收集,测定土壤根系固碳量。研究结果显示,1)在烤烟生长季,植烟土壤呼吸动态呈倒"S"型的先下降后上升再下降的变化规律,施用有机肥增加了土壤呼吸强度,尤其是在有机肥施用初期。2)烤烟生长季碳排放量平均为385.84 kg·hm^-2,不同处理碳排放量表现为对照293.11 kg·hm^-2,秸秆396.9 kg·hm^-2,农家肥363.36 kg·hm^-2,油枯422.98 kg·hm^-2,油枯+农家肥452.84kg·hm^-2。3)不同碳源分解速率差异较大,生长季分解系数为0.22~0.42,秸秆和农家肥分解系数低于油枯。4)有机肥的施用对烤烟根系碳积累量的提升效果不明显,而各有机肥处理相比,农家肥以及农家肥与油枯混施相对于秸秆处理能够显著增加烤烟根系碳积累量。5)当地耕作模式下,整个生育期有56.42%的烤烟根系残留于土壤,可补偿土壤碳260.56 kg·hm^-2,烤烟根系碳是常规施肥下土壤碳的主要来源。6)常规施肥下,单施化肥植烟土壤表现为碳源,有机无机配施下植烟土壤表现为碳汇。有机肥的施用能够提升土壤碳平衡,减少碳损失;采用农家肥与油枯混施也能够在一定程度上促进烤烟根系碳积累的提升。     

中国地区小麦产量及产量要素对秸秆还田响应的整合分析

为探究秸秆还田对中国小麦的增产效果,运用整合分析方法定量分析秸秆还田后小麦产量及产量要素的变化范围,并探讨不同秸秆还田条件的影响;通过文献检索与严格筛选,整理得到55篇田间试验数据资料,建立小麦产量及产量要素数据库,并应用整合分析方法,比较分析秸秆还田对小麦产量和产量要素的整体影响以及秸秆还田技术的适用条件。结果表明,总体上秸秆还田能够显著增加小麦产量和产量要素,但增长幅度不大。通过分析其影响因素发现,在黄河流域到长江流域之间的省份,选择潮土、塿土、水稻土等养分中等、复杂难以利用的土壤类型,实行秸秆还田技术的收益较好;不同耕作方式对秸秆还田的影响较大,免耕和翻耕技术好于旋耕技术;施氮水平>300 kg·hm^-2时,增产不显著,200～300 kg·hm^-2施氮水平为最佳;秸秆种类与还田量对小麦的增产效果影响较大,其中使用麦秸还田效果一般,稻秸全量或半量还田成效较好,玉米秸半量还田(6 000 kg·hm^-2)增产最大。综上,秸秆还田能够增加小麦产量和产量因素,秸秆还田的最佳条件为在秦岭-淮河一线南北地区实行免耕与翻耕交替耕作方式,采用玉米秸秆半量还田方法,施氮水平为200～300 kg·hm^-2。本研究结果为秸秆还田在我国小麦高产高效技术的应用提供了理论参考。     

秸秆直接还田与炭化还田下土壤有机碳稳定性和温室气体排放潜力的对比研究

选取北方旱地和南方水田两种不同农业利用方式的土壤为研究对象,分别在旱地和水田设置了无秸秆还田(NR)、秸秆直接还田(SR)和秸秆转化为生物质炭还田(BR)三种处理,在作物收获后,采集对应处理的土壤通过室内培养对比研究了秸秆直接还田和生物质炭还田下土壤有机碳的稳定性及温室气体排放潜力的变化。研究结果表明:秸秆直接还田与生物质炭还田均可显著增加土壤有机碳和全氮含量,但不同处理下的土壤有机碳稳定性存在显著差异。从有机碳的矿化量和矿化率来看,生物质炭还田处理与秸秆直接还田处理相比,分别降低旱地、水田土壤矿化量的36.0%、21.5%和矿化率的47.0%、34.7%;水田与旱地相比,表观上水田矿化显著高于旱地土壤,但从土壤有机碳矿化率来看,水田土壤各处理均显著低于旱地土壤相同处理的19.0%、26.2%和9.2%。不同处理显著影响土壤N2O的释放,无论旱地还是水田土壤,与秸秆直接还田相比,施用生物质炭均显著降低土壤N2O的释放;进一步分析土壤产生的综合温室效应(GWP)表明,生物质炭还田下的GWP比秸秆直接还田显著降低39.6%和28.5%。因此,秸秆转化为生物质炭后还田可作为一项重要的农田土壤固碳减排措施进行秸秆利用。     

基于大比例尺数据库的福建省耕地土壤固碳速率和潜力研究

明确土壤固碳速率和潜力是制定耕地固碳减排措施的基础。以我国典型亚热带地区—福建省不同地理位置的闽侯、浦城、同安、武平和永定5个县为研究区,运用生物地球化学过程模型DNDC（DeNitrification and Decomposition）,模拟这5个县在目前区域尺度最详细的1:5万土壤数据库下1980─2009年和2010─2039年有机碳动态变化,并运用尺度上推的方法估算出全省耕地土壤固碳速率和潜力。结果表明,福建省耕地土壤1980─2009年的固碳总量为7.37 Tg,而2010─2039年的固碳潜力为7.04 Tg,两个时段的年均固碳速率分别为：190 kg·hm-2和176 kg·hm-2,说明目前的农田管理措施有利于研究区长期固碳。其中,水稻土和盐渍水稻土分别在土类和亚类级别中固碳速率最大,不同时段均大于175 kg·hm-2·a-1;而红壤在土类和亚类级别中固碳速率皆最小,不同时段均小于3 kg·hm-2·a-1。总体来看,1980─2009年和2010─2039年水稻土的固碳总量均占全省耕地固碳总量的92%以上,是今后制定固碳减排措施的重点。     

长江中下游地区耕地土壤有机碳密度变化率驱动因素

为探究长江中下游地区耕地土壤固碳增汇措施,该研究收集与整理长江中下游地区59处长期定位试验观测数据,量化不同类型耕地土壤有机碳密度变化率的差异特征,运用随机森林模型与线性规划探究土壤有机碳密度变化率的驱动因素与提升途径。结果表明:水田和旱地土壤有机碳密度变化率范围分别为-1 548.15～3 577.10 kg/(hm²·a)和-261.89～3 245.01 kg/(hm²·a),差异不显著(P=0.85)。有机肥氮量、土壤pH值、化肥氮量、秸秆氮量对水田土壤有机碳密度变化率的影响较大;有机肥氮量和化肥氮量对旱地影响较大。因此,建议长江中下游地区可通过有机无机肥科学配施,合理调控水田土壤pH值和秸秆还田量。该研究可为长江中下游地区耕地固碳增汇的技术推广提供参考。     

氮肥减施和秸秆还田对土壤固定态铵含量的影响

【目的】固定态铵作为土壤氮素的暂存库,其含量的变化能够影响土壤的保氮供氮功能,而深入探究氮肥减施对土壤固定态铵的影响及其对秸秆还田的响应,可为优化农田氮肥管理提供理论依据。【方法】依托位于中国东北黑土区玉米种植系统连续9年全量玉米秸秆覆盖归还的保护性耕作试验平台,通过设置玉米秸秆不还田(S0)、秸秆还田量33%(S33)和秸秆全量覆盖还田(S100)3个秸秆还田量处理,以及240 kg hm^-2(N240)、190 kg hm^-2(N190)、135kg hm^-2(N135)、0 kg hm^-2(N0)4个氮素施用水平,研究氮素减施3年后土壤固定态铵总量的变化以及不同秸秆还田量对固定态铵的影响。【结果】秸秆不还田时,土壤固定态铵总量随施氮量降低而逐渐下降,且在不施氮肥处理(N0)时显著低于施氮肥处理;在S33N190时土壤-作物系统出现氮素缺乏,并且随施氮量的下降土壤固定态铵降低量与氮素缺乏量之间具有显著的正相关关系。在所有氮肥水平,秸秆还田尤其是全量秸秆还田均有利于缓解固定态铵的释放,但在N135...     

保护性耕作下农田表土有机碳含量变化特征分析——基于中国农业生态系统长期试验资料

本文收集整理1979--2008年有关中国保护性耕作的长期试验文献,整合分析了长期保护性耕作下中国农田表土有机碳的变化特征。采用的48篇有效文献涉及18个省（区、市）的59个长期试验点,涵盖12种土类。总样本88个（其中早地51个,水田37个）。结果表明,保护性耕作处理下旱地和水田表土有机碳年变化分别介于一0．30～0．75g·kg^-1·a^-1和-0．20～2．71g·kg^-1·a^-1,平均增幅分别达0．21g·kg^-1·a^-1和0．51g·kg^-1·a^-1。可见长期保护性耕作下,农田表土有机碳含量总体呈上升趋势,水田下增长高于旱地。和少免耕相比,秸秆还田更有利于促进表土有机碳的积累。统计分析还表明,结合秸秆还田的综合保护性耕作措施可以使水田和早地的有效固碳期限分别持续27a和23a,水田在保持较高固碳速率的同时,延长了有效固碳年限。耕地表土有机碳含量在保护性耕作下特别是秸秆还田可以较大幅度地提高,实行保护性耕作可以具有农业稳产与土壤固碳的双重意义。     

秸秆还田年限及还田量对稻田净温室效应的影响

本文研究了不同秸秆还田年限（2 年和13 年）和还田量（0、1.6 、3.2和4.8 t/hm2）对稻田CH4和N2O排放、土壤固碳速率和净温室效应的影响。结果表明：稻田CH4排放量在第2年和第13年均随秸秆还田量的增加呈线性增加，但第13年单位秸秆还田量对CH4排放的平均促进效应比第2年降低3%；各处理N2O排放量在第2年无显著差异，第13年显著促进N2O排放55% ~ 171%，且随秸秆还田量的增加呈线性增加；土壤固碳速率在第2年随秸秆还田量的增加呈线性增加，但第13年下降80% ~ 84%，且各处理间无显著差异；净温室效应随秸秆还田量的增加呈线性增加，但从第2年到第13年经历了从汇到源的过程，这说明秸秆还田量对净温室效应的影响受还田年限调控，其增加的温室效应逐步完全抵消了土壤固碳的减排效益，加剧了全球气候变暖。因此，稻田在长期秸秆还田条件下是一个重要的碳源，亟待优化秸秆还田技术，进一步固碳减排，以实现农业可持续发展。     

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