基于SWAT模型的长江源土地利用/土地覆被情景变化对径流影响研究

土地利用/土地覆被变化对流域水资源循环过程及配置影响显著。为了研究土地利用/土地覆被情景变化对径流影响情况,以长江源流域为例,构建了适合该流域的分布式水文模型(SWAT),并模拟了不同土地利用/土地覆被情景下的流域年均径流量和径流深。模拟结果如下:当流域林地和草地面积增加到最大,径流量减少了16.7%,达到304.12m3/s,径流深减少14.02mm;当林地和草地面积减少,并逐步变为沙地、裸地,流域径流量增加16.1%,达到424.32m3/s,径流深也增加了13.49mm;当林地和草地面积减少到无植被覆盖,将使流域径流量增加28.4%,达到469.67m3/s,径流深增加23.88mm;在草地覆被最佳状况下,径流量有所增加,但增加幅度不大,只有5.6%,达到385.98m3/s,径流深增加4.72mm。综上所述,长江源流域林地和草地面积增加,导致径流减少,而沙地和裸地面积增加导致径流量增加。     

基于SWAT模型的张家口清水河流域土地利用情景变化对径流影响研究

土地利用是区域气候和环境变化的重要影响因素。以3S技术为依托,分析25年来张家口清水河流域土地利用类型变化特征,建立了流域SWAT模型并评价了其在张家口清水河流域的适用性,通过设置5种土地利用变化情景,定量分析了张家口清水河流域主要土地利用类型对流域径流的影响。结果表明:SWAT模型在张家口清水河流域具有很好的适用性。1990—2015年,张家口清水河流域的土地利用类型以林地、草地和耕地为主,3种土地利用类型面积总和均占流域总面积的96%以上。其中林地对径流量的影响系数为1.908 m~3/(km~2·h),草地对径流量的影响系数为1.836 m~3/(km~2·h),说明林地和草地都具有截留径流的作用,且林地的作用大于草地;耕地对径流量的影响系数为3.168 m~3/(km~2·h),说明耕地对径流起增加作用。因此,合理开发耕地资源,保护林草资源有利于促进张家口清水河流域生态环境质量的改善。     

基于SWAT模型的丹江流域土地利用变化对径流影响研究

为定量分析土地利用类型变化对径流的影响,基于SWAT模型,通过分析丹江流域近20年来的土地利用变化,并设置3种不同土地利用情景模式,探究了土地利用类型对流域径流的影响作用。结果表明:SWAT模型率定期和验证期的决定性系数R²和纳什效率系数NS分别为0.8,0.73和0.86,0.78,适用于丹江流域径流模拟。2000—2020年,丹江流域土地利用变化引起的径流变化为-0.18%; 情景1中,把林地、草地全变为耕地的情况下,模拟的年均径流变化率为61.65%,情景2中,把耕地和草地全转换为林地的情况下,模拟的年均径流变化率为-12.69%,情景3中,把耕地和林地全转换为草地的情况下,模拟的年均径流变化率为24.24%。耕地对径流深度的影响系数为0.26 mm/hm²,林地对径流深度的影响系数为-13.35 mm/hm²,草地对径流深的影响系数为-0.01 mm/hm²。由此得出,耕地对产流起促进作用,草地和林地对产流起抑制作用。为维护丹江流域生态环境,增强丹江流域径流供给,应科学开发耕地资源。     

土地利用和气候变化对流溪河水库流域径流的影响

[目的]探究径流对土地利用与土地覆被变化(LUCC)和气候变化的响应，为华南地区流溪河水库流域未来水资源的合理利用开发及社会经济可持续发展提供依据。[方法]通过构建分布式生态水文模型CHESS和设置情景模式，定量分析了土地利用和气候变化对径流的影响，同时结合CA-Markov模型，对流域未来径流变化进行了预测。[结果]CHESS模型在流溪河水库流域径流模拟中有很好的适用性，率定期的纳什系数(NS)为0.82,R²为0.91,验证期的NS为0.74,R²为0.86;土地利用变化方面，耕地转化为林地或草地会导致年均径流量减少，林地或草地转化为耕地会导致年均径流量的增大，耕地、林地、草地对径流形成的贡献能力为耕地>草地>林地；气候变化方面，年均径流量与降水量成正比，与温度成反比；2000—2020年，流域年均径流量逐渐增大，气候变化促进了径流的形成，土地利用变化抑制了径流的形成，且气候变化的影响占主要地位；未来预估情景下，2030年、2050年流域内建筑用地面积会增大，林地、草地面积会减小，耕地、水体面积变化不大，且在2040—2050...     

修河中上游流域土地利用变化对径流的影响

[目的]土地利用的变化对流域水文过程产生了重要的影响,研究土地利用变化下的水文响应已成为水文学科研究的一个热点。[方法]以修河中上游流域作为主要研究区域,分析了35年来修河中上游流域各种土地利用类型的变化特征,并利用1987—2000年水文气象数据资料,构建了SWAT模型,通过设置1980年、1990年、2005年和2015年4种土地利用情景,定量分析了修河中上游流域土地利用变化对径流的影响。[结果]SWAT模型在研究区具有较好的适用性。1980—2015年,修河中上游流域主要用地类型为林地、耕地和草地,三者面积之和占流域的98%。其中高利用城市用地和耕地对径流的影响系数是正值,说明高利用城市用地和耕地对径流起促进作用;林地、草地对径流的影响系数均表现为负值,说明林地和草地对径流有抑制作用,且草地的抑制作用更加显著。此外,林地和草地在丰水季会减少径流,在枯水季却会增加径流,有类似海绵的作用。[结论]模拟研究土地利用变化对修河中上游流域径流的影响在合理规划水土资源、改善生态环境方面具有十分重要的现实意义。     

渭河流域径流对土地利用变化的时空响应

为定量分析渭河流域土地利用变化对径流的时空影响,该文基于渭河流域1985年,1995年和2005年3期土地利用数据,分析了流域近20 a的土地利用变化特征,结合SWAT(soil and water assessment tool)水文模型,设置5种土地利用变化情景,研究了流域土地利用变化与年、季径流的响应关系。结果表明,SWAT模型在渭河流域有较好的适用性;耕地、林地和草地为流域主要土地利用类型,面积变化小于10%,但它们在空间上的位置发生了较大转移;流域近20 a土地利用变化对径流影响小于15%;极端土地利用情景下,产流量总体趋势为耕地草地林地。退耕还林对年、季径流的影响程度均为干流大于支流,退耕还草对年径流(干流中游、下游、泾河)和季径流(冬季)的影响程度较大。该研究成果对于流域土地利用格局的合理规划及极端水文事件的控制具有重要意义。     

1980—2020年渭河中上游流域土地利用演变及其对径流的影响

[目的] 研究渭河中上游流域不同土地利用情景下径流的响应规律,为渭河中上游流域的发展规划及水资源管理提供科学支撑。[方法] 基于1980—2020年土地利用数据,分析流域40 a的土地利用变化特征,并结合SWAT模型,设置5种历史土地利用情景、两种综合土地利用情景和3种极端土地利用情景,探究径流在不同土地利用情境下的响应。[结果] ①流域40 a间耕地、水域及未利用土地面积逐渐减小,林地、草地和居民用地面积逐渐增加。②1980—2020年共5个时期模拟年均径流深分别为72.24,72.27,72.31,71.86,72.25 mm,退耕还林、退耕还草、耕地型、林地型及草地型模拟年均径流深分别为68.59,69.70,72.60,64.81,66.82 mm。[结论] 40 a间土地利用类型的变化对渭河中上游流域径流的影响小于10%;退耕还林、退耕还草对径流主要起抑制作用。在3个极端土地利用情境下径流大小为：耕地型＞草地型＞林地型,且耕地型与林地型、草地型情境下的差异明显。     

基于SWAT模型和SUFI-2算法的石羊河流域月径流分布式模拟

[目的]揭示石羊河流域径流量对土地利用变化的响应机制,为旱区水资源的合理配置和优化利用提供理论依据。[方法]利用石羊河流域DEM、气象、土壤、1995与2000年2期土地利用等数据,结合RS和GIS技术,构建SWAT分布式水文模型。基于SWAT模型及SUFI-2算法,对石羊河流域1980—2009年的月径流过程进行模拟。[结果]流域内1995与2000年土地利用均以耕地、林地、城乡工矿居民用地面积显著增加,草地、水域、未利用地减少为主;影响SWAT模型模拟效果前3位的参数分别是CN2,Alpha_Bf,Timp;校正期和验证期月流量的模拟值和实测值拟合较好,其Nash Suttcliffe系数Ens和相关系数R2均大于0.8,相对误差|Re|均小于10%。[结论]采用SUFI-2算法的SWAT模型在石羊河流域月径流模拟中具有一定程度的适宜性。     

基于SWAT模型的南渡江流域土地利用/覆被变化的径流响应

为了探究热带岛屿性流域土地利用/覆被变化(Land Use/Cover Change,LUCC)的水文效应,以海南岛典型热带岛屿性流域南渡江流域为研究区,构建本地化SWAT模型,模拟流域水文过程及其对LUCC的响应,揭示流域径流的变化规律,对比不同土地利用类型的水文过程及调蓄能力,探讨了典型热带岛屿性流域LUCC的径流效应。结果表明:SWAT模型在南渡江流域的适用性良好,径流模拟对植被蒸散发、产生径流的坡面状况、土壤状况和地下水过程较敏感。不同土地利用类型对流域的产流贡献顺序为耕地>其他林地>橡胶林地; 耕地产流能力最强,其他林地和橡胶林地具有一定的截流蓄水作用。综上所述,与1990年相比,2015年南渡江流域河流径流量减少,流域LUCC导致的地表径流减少是河流径流量减少的直接原因,而蒸散发加剧是地表径流减少的主要原因。     

基于SWAT模型的衢江流域土地利用变化径流模拟研究

以衢江流域作为研究对象,收集流域植被、气候、土壤、水文和地图资料,基于ArcGIS 10.3平台建立了衢江流域SWAT(Soil and Water Assessment Tool)模型。结果表明:率定期和验证期模拟月径流与实测值的相关系数(R2)大于0.83,纳什系数(Ens)大于0.69,模型可以较好地模拟衢江流域径流过程。2000—2015年衢江流域土地利用类型均以林地和农地为主,二者约占流域总面积的98%,其他土地利用类型面积合计不足2%;研究时段内,建设用地面积大幅增加,其他土地利用类型变幅较小。2000年、2005年、2010年、2015年四期土地利用情景下月径流过程变化趋势基本一致,2015年径流量比2000年增加0.27%,水量平衡各分量在四期土地利用情景下差值为1.1～3.8mm。不同情景模拟分析发现,流域内草地面积较小,草地转化为林地对地表径流和水量平衡的影响较小,而农地全部转化为林地,地表径流比当前土地利用模式减少15.0%,同时深层水分渗漏增加5.7%。因此,2000—2015年土地利用方式的微小变化不会显著影响衢江流域径流和水量平衡,研究区林地面积持续增加,将进一步减少地表径流,增加深层水分渗漏,补给地下水。     

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