基于USLE的广东省山区土壤侵蚀量估算及特征分析

基于通用土壤流失方程(universal soil loss equation,USLE)、遥感和ArcGIS空间分析技术,通过合理选择USLE模型中各土壤侵蚀因子的计算方法,对广东省山区土壤侵蚀量进行了估算,并对山区土壤侵蚀随土地利用类型、土壤类型、坡度及海拔高度的分布特征进行了分析。结果表明,广东省山区2000年土壤侵蚀总量为1.23×10⁸ t,年均侵蚀模数为1 080t/(km²·a),侵蚀强度为轻度。不同土地利用类型中,旱地的侵蚀强度最高,达2 055t/(km²·a),林地和草地的侵蚀模数较小,分别为908和932t/(km²·a)。不同坡度等级的土壤侵蚀特征表现为坡度越陡,侵蚀强度越大。不同海拔高度的侵蚀特征表现为在0~1 600m高度,侵蚀强度随海拔高度的升高而增大;海拔高于1 600m时,侵蚀强度随海拔高度的升高而下降。     

耕作及轮作对土壤氮素径流流失的影响

5年轮作和1年水平沟耕作试验表明:在不同的坡度上,与传统耕作法相比,水平沟减少产流7%,径流液铵态氮浓度提高19%,流失量达到13.01kg/(km²·a),比传统耕作多流失1.11kg/(km²·a);径流硝态氮浓度减少27%,比传统耕作减少7.68kg/(km²·a);径流硝态氮流失减少量和铵态氮增加量相差6倍,水平沟可减少6.57kg/(km²·a)矿质氮流失;水平沟拦截泥沙25%左右,泥沙中全氮富集率提高13%,土壤全氮流失457kg/(km²·a),平均减少18%;一季黑豆和一季黄豆及两季黑豆和一季黄豆参与的5年轮作周期,土壤侵蚀量仅为896t/(km²·a)和984t/(km²·a),不及糜子和土豆参与轮作周期的1/2.     

生态扶贫背景下退耕还林生态产品的经济效益——以核桃和茶树林为例

[目的] 将生态效益纳入成本效益分析,从生态和经济的角度研究退耕还林生态产品价值,为相关地区生态扶贫工作的顺利开展提供决策依据。 [方法] 分别以安徽省和四川省的退耕还茶树林和核桃林为研究对象,将水土保持作为退耕还林的主要生态产品,利用通用土壤流失方程计算其实物量和价值量,并将价值量作为收益的一部分纳入经济分析。 [结果] ①与裸地相比,研究区茶树林和核桃林均可有效减少土壤侵蚀,20 a累计减少侵蚀量分别为3.06×10⁴ t和2.12×10⁵ t。 ②茶树林和核桃林的单位面积水土保持价值分别为681.0和1 285.5元/(hm²·a)。将该价值纳入经济分析后,平均净收益分别为61.3和129.3万元/a,单位面积年均净收益分别为18.43和9.75万元/hm²。 ③退耕还林补助标准对净收益影响较小。标准提高1倍后,预期净收益分别下降2.1%和4.6%。林产品价格减半后,预期净收益分别下降68.1%和77.1%。 ④茶树林和核桃林的生态效益分别占成本的4.4%和6.8%,最高比例达11.9%。 [结论] 经济林的生态效益可以抵消部分成本,应纳入经济分析净收益计算,实现生态产品价值。     

南方稻区绿肥生态服务功能及生态价值评估研究

为探究我国南方稻区绿肥种植的生态服务价值,本文以我国南方稻区农田引入绿肥紫云英为例,界定了稻田种植紫云英的生态服务功能,并运用实际市场法、替代市场法和虚拟市场法等研究方法,构建了绿肥生态价值评估的理论模型,核算了绿肥的生态服务价值,得到了以下研究结论：1）南方稻区绿肥生态服务功能主要涉及调节和支持两类,调节服务包括气体调节、水分涵养和土壤保持3种功能,支持服务则包括土壤有机质累积和土壤营养物质循环两种功能;对应地,南方稻区农田轮作冬绿肥紫云英的生态价值也被界定为以上5种。2）南方稻区冬闲田种植紫云英在一个轮作周期中能够产生1.125万元·hm^-2的生态价值,其中,气体调节价值最大,为0.380万元·hm^-2,其次是土壤有机质累积价值,为0.279万元·hm^-2,营养物质循环价值和土壤保持价值分别为0.204万元·hm^-2和0.214万元·hm^-2,土壤水分涵养价值最小,为0.048万元·hm^-2。3）南方稻区绿肥种植投入成本为0.173万元·hm^-2,绿肥种植所产生的生态价值是种植投入成本的6.5倍。研究表明农田冬种绿肥紫云英的生态服务价值是客观存在的。该研究为南方稻区绿肥引入冬闲田后生态价值的评估提供了较为科学的研究方法和基础参数,同时,也为未来政府制定绿肥种植的生态补偿机制提供了理论依据。     

太湖流域春季不同土地利用类型蒸散速率的比较

运用静态箱/红外气体分析仪法(static chamber/IRGA),研究了太湖流域茶园、油菜地、小麦地和撂荒地4种不同土地利用类型春季蒸散速率的变化特征,分别对3-5月不同生育期以及6：00-15：00不同时段4种土地利用类型蒸散速率进行了比较。结果表明,太湖流域春季不同土地利用类型蒸散速率总体呈现逐渐增大的趋势,但茶园修剪后蒸散速率大幅下降(36.73%),油菜地在始花期亦突现一峰值〔2.14mmol/(m²·s)〕;4种土地利用类型蒸散速率的日变化呈以12：00-15：00为峰值的单峰曲线,但茶园修剪后蒸散速率的日变化平缓,油菜地和小麦地蒸散速率的日变化幅逐渐增大。4种土地利用类型3-5月蒸散速率日均值从大到小依次为：茶园〔2.24mmol/(m²·s)〕 > 油菜地〔1.48mmol/(m²·s)〕 > 小麦地〔1.28mmol/(m²·s)〕 > 撂荒地〔1.16mmol/(m²·s)〕;3月下旬12：00-15：00,以及4月中旬9：00-15：00为茶园蒸散速率极显著高于油菜地、小麦地和撂荒地的关键时期,差异最大。     

广西石灰岩地区水土流失及其治理措施的探讨

广西石灰岩分布较广,喀斯特现象发育,山多石头多,土地零散坡地多,成土缓慢,土层薄。石灰岩地区土壤允许流失量仅为68t/(km²·a),而现在该区土壤流失量一般为100～200t/(k²m·a),大大超过允许流失量。作者针对广西实际情况提出并论述了:1.造林绿化;2.封育恢复植被;3.修筑石坎梯田;4.增施肥料,深翻改土;5.建立生态目标责任制等水土保持措施。     

南水北调中线水源地土壤侵蚀经济损失估算

在GIS的支持下,通过气象数据分析、实地调查、野外采样及室内分析、DEM计算、遥感解译等,构建了南水北调中线水源地丹江口水库库区流域地理信息数据库,并利用USLE估算了研究区的土壤侵蚀量。以1990年的价格为基准,利用市场价格法、机会成本法和影子工程法估算了水源区年均土壤侵蚀带来的经济损失。结果表明,水源区的年均土壤侵蚀模数为2394 t/(km²·a)。研究区表土流失造成的全氮、全磷、全钾和有机质损失量在分别换算成标准化肥磷酸二铵、氯化钾及薪柴后的经济损失分别为1.64×10⁸,7.25×10⁷,1.17×10⁹和2.97×10⁷元;年均侵蚀的土壤相当于61.94 km²的土地被废弃,经济损失为3.71×10⁷元。土壤侵蚀导致的涵养水分、泥沙淤积和泥沙滞留方面的经济损失分别为3.22×10⁵,1.88×10⁷和1.95×10⁶元。水源区年均土壤侵蚀总经济损失达1.50×10⁹元,其中养分损失占96.11%。     

基于GIS与RUSLE的榆林市土壤侵蚀空间分布研究

利用3S技术,采用美国通用的水土流失方程(RUSLE),对榆林市2001和2010年的土壤侵蚀状况及其空间分布特征进行了计算分析。结果表明,榆林市2001年平均土壤侵蚀模数为4411 t/(km²·a),年均侵蚀总量为1.93×10⁸t;2010年的平均土壤侵蚀模数为6237 t/(km²·a),年均侵蚀总量为2.72×10⁸t。2001-2010年榆林市各区县的土壤侵蚀变化状况有着明显的空间差异,府谷、神木、榆阳、横山、靖边、佳县和子洲7个区县的土壤侵蚀类型发生了由中强度向高强度侵蚀的转化,土壤状况不断恶化。而定边、米脂、吴堡、绥德和清涧5县的土壤侵蚀类型由高强度向低强度侵蚀转变,水土流失状况得到有效遏制。     

生态工程对科尔沁沙地主要生态服务功能的影响

[目的] 研究生态工程实施下科尔沁沙地主要生态服务功能的变化特征,为该区今后生态保护建设提供科学依据。[方法] 运用已有的生态服务评估方法定量评估了2001—2018年科尔沁沙地固碳量、水源涵养及水土保持服务功能的时空变化情况。[结果] ①科尔沁沙地土地利用类型主要以耕地、林地和草地为主,生态工程实施期间,林地、耕地面积分别增加8 448 km²,3 280 km²,草地面积减少12 639 km²; ②科尔沁沙地固碳量稳步增长,林地和耕地的固碳量均增加,草地的固碳量减小,但草地固碳量依然最高; ③科尔沁沙地水源涵养量呈先增加后略微减少的趋势,所有土地类型中林地水源涵养量持续升高; ④科尔沁沙地水土保持量持续上升,约增加1.38×10⁷ t,林地水土保持量增加最显著。受地势的影响,区域水土保持总量呈西高东低的分布特征。[结论] 科尔沁沙地生态工程建设效果良好,创造了显著的生态效益。     

基于GIS的福建省水土保持功能重要性评价

[目的] 对福建省水土保持功能重要性进行评价，为该省生态保护红线划定提供科学参考。[方法] 基于GIS技术，利用降水、土壤、数字高程和植被指数等数据，采用修正通用水土流失方程（RUSLE），估算福建省土壤保持量，并对其分级。[结果] 全省土壤保持总量为2.65×10⁹ t/a，平均土壤保持模数为20 789.82 t/（km²·a）。水土保持功能极其重要区、高度重要区、中等重要区、较为重要区和一般重要区面积分别为3 192.54，8 205.54，15 547.71，21 519.81，74 000.20 km²，分别占全省面积的2.61%，6.70%，12.70%，17.57%和60.42%。[结论] 福建省水土保持功能极其重要区、高度重要区和中等重要区主要分布在闽西和闽中2大山带及其周边丘陵山地区。     

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