淮北矿区地表拉张裂隙区耕地土壤主要养分特征

[目的] 分析采煤沉陷导致的地表拉张裂隙对耕地土壤质量的影响,评估采煤沉陷前后土壤养分变化,为沉陷区土地采前—采中治理提供理论基础。[方法] 以淮北矿区孙疃矿地表拉张裂隙区为研究区域,分别在沉陷前(2019年6月)、沉陷后(2019年12月、2020年7月)采集样品,沉陷前布设5个采样点(T₁—T₅),沉陷后选择两条典型纵向拉张裂隙,由沉陷斜坡坡顶到坡底将沉陷区划分为A,B,C 3个分区,在裂隙两侧设置13个采样点,每个采样点沿深度方向每隔20 cm采集一个土壤样品,分别测试含水率、有机质、速效钾、速效磷、全氮和全磷含量6个指标。[结果] 拉张裂隙区两次采样土壤含水率、有机质、速效钾、全磷含量存在显著差异(p＜0.01),速效磷和全氮差异性不显著(p＞0.05);通过主成分分析得到研究区第一、二主成分分别为有机质、全氮、全磷(受负面影响)和含水率、速效钾(受到正面影响);根据综合养分评价—主成分分析法发现裂隙区综合养分与对照点相比总体下降,但拉张裂隙区内养分从沉陷斜坡坡顶至坡底逐渐上升。[结论] 地表拉张裂隙在采煤沉陷区分布广泛,是造成沉陷区耕地质量下降的主要原因。     

采煤沉陷区不同土地利用类型土壤水分、有机质和质地的空间变异性

探索采煤沉陷区坡面微地形上土壤水分、养分和颗粒迁移转化的作用机理,为促进矿区生态环境综合整治的科学决策提供重要的理论和实践价值。以焦作九里山矿典型平原型采煤沉陷坑内的耕地和林地为研究对象,对比分析了土壤含水率、有机质含量和质地在不同土地利用类型(耕地和林地)、沉陷坡位(中心、坡底、坡中、坡顶和对照)和剖面深度(0~10 cm、10~20 cm、20~30 cm、30~40 cm、40~50 cm)上的空间变异性。结果表明,耕地土壤含水率和黏粒含量较林地显著降低(p0.05),而砂粒含量则显著增加(p0.01)。坡中或坡底处的土壤含水率、有机质和粉粒含量最小,而砂粒和黏粒含量则最大,成为整个沉陷坡面上的极值点。在剖面深度上,土壤含水率、有机质、砂粒含量表现为显著的表层聚集,黏粒含量则为显著深层聚集的特点。通过对土壤含水率、有机质含量和土壤质地在沉陷区坡面微地形空间变异作用机理的分析,建议平原型采煤沉陷区的土地复垦方向应以耕地为主、林地为辅的基本原则,在坡中到坡底的等高段复垦为林灌地,能起到对沉陷区土壤水分与养分流失控制和生态环境效益改善的关键作用。     

采煤沉陷区不同土地利用类型土壤水分、有机质 和质地的空间变异性

探索采煤沉陷区坡面微地形上土壤水分、养分和颗粒迁移转化的作用机理,为促进矿区生态环境综合整治的科学决策提供重要的理论和实践价值。以焦作九里山矿典型平原型采煤沉陷坑内的耕地和林地为研究对象,对比分析了土壤含水率、有机质含量和质地在不同土地利用类型（耕地和林地）、沉陷坡位（中心、坡底、坡中、坡顶和对照）和剖面深度（0~10 cm、10~20 cm、20~30 cm、30~40 cm、40~50 cm）上的空间变异性。结果表明,耕地土壤含水率和黏粒含量较林地显著降低（p<0.05）,而砂粒含量则显著增加（p<0.01）。坡中或坡底处的土壤含水率、有机质和粉粒含量最小,而砂粒和黏粒含量则最大,成为整个沉陷坡面上的极值点。在剖面深度上,土壤含水率、有机质、砂粒含量表现为显著的表层聚集,黏粒含量则为显著深层聚集的特点。通过对土壤含水率、有机质含量和土壤质地在沉陷区坡面微地形空间变异作用机理的分析,建议平原型采煤沉陷区的土地复垦方向应以耕地为主,林地为辅的基本原则,在坡中到坡底的等高段复垦为林灌地,能起到对沉陷区土壤水分与养分流失控制和生态环境效益改善的关键作用。     

微地形对天津滨海吹填土土壤理化性质和植被状况的影响

通过对吹填土6%坡度8%的典型微地形的田间试验研究,分析了微地形坡面(坡底、坡腰、坡顶)对滨海吹填土土壤盐分、养分和植被生长状况的影响。结果表明,吹填1~2 a内,微地形条件形成的坡底湿润区有利于先锋植物碱蓬的着陆和生长,使得碱蓬盖度和生物量坡底湿润区坡腰半湿润区坡顶干旱区,而碱蓬在生长过程中对钠离子的选择性吸收,显著降低了坡底土壤的含盐量和ESP;碱蓬根系的疏土作用,使土壤通气性增强、微生物活动加剧,土壤有机质分解量大于归还量,导致坡底表层土壤有机质的含量远低于坡腰和坡顶;同时碱蓬生长对养分的吸收,导致坡底处速效磷和速效钾含量的快速下降。     

~(137)Cs示踪采煤沉陷坡土壤侵蚀及其对土壤养分的影响

为更好地理解矿区土壤退化机理,该文利用137Cs技术研究了焦作矿区具有15a沉陷历史的采煤沉陷坡土壤侵蚀特征及其对土壤养分的影响。沉陷坡137Cs含量从坡顶到下坡逐渐降低,及至坡脚急剧增大且表现出最高的值。基于137Cs本底(1 645 Bq/m2),沉陷坡坡顶至下坡表现为土壤侵蚀,而坡脚为土壤沉积。沉陷坡土壤侵蚀高达3.75 kg/(m2·a),属于中度侵蚀。沉陷坡土壤黏粒含量沿下坡方向增加,表明水蚀的分选性搬运。与对照区相比,沉陷坡侵蚀区土壤总有机碳(total organic carbon,TOC)、水溶性有机碳(water-soluble organic carbon,WSOC)、全氮、碱解氮、全磷、有效磷含量均出现了显著降低(P0.05);沉积区除WSOC显著降低(P0.05)外,其他养分含量变化不明显(P0.05)。在沉陷坡的侵蚀区,TOC与WSOC含量沿下坡方向逐渐减小,表现出与137Cs一致的分布格局;其他养分含量的坡面变化与137Cs分布不一致。相较于对照区,WSOC/TOC与碳氮比、碳磷比在沉陷坡侵蚀强烈的坡位分别出现了显著增大与降低(P0.05)。研究结果表明:1)焦作矿区自采煤沉陷坡形成以来发生了较严重的水蚀;2)侵蚀引起的土壤再分配影响沉陷坡土壤碳、氮、磷动态,其中,土壤再分配对土壤碳动态的影响最强;3)在土壤侵蚀作用下,采煤沉陷坡侵蚀强烈的坡位土壤有效态碳、氮、磷养分潜在的侵蚀风险大。采煤沉陷坡土壤侵蚀及其对土壤养分的不利影响应引起矿粮复合区土地整治的关注。     

开采沉陷对耕地土壤化学特性影响的空间变化规律

为了给煤矿沉陷耕地的复垦治理提从理论依据,以山东省兖州矿区为例,对沉陷耕地不同下沉位置不同土层的土壤进行了测定和分析,揭示了开采沉陷对时土壤化特性影响的空间变化规律,结果表明,开采沉陷显著影响耕地表层土壤的化学特性,沉陷耕地上中坡1.5m结合处土壤有机质和养分下降的幅度最大,并在坡底积聚,同时坡底土壤有盐渍化趋势,在土壤化学特性中,受到采沉隐影响最大的是土壤盐水,其次是土壤全氮为和机质,再次是土壤速效磷和速效钾,而土壤酸碱性受其影响较小。     

林地开垦对黄土区坡面土壤养分空间分布的影响

研究黄土高原侵蚀环境下林地开垦后坡面土壤养分空间分布状况,确立林地开垦后侵蚀驱动的坡地土壤养分空间变异特征。以黄土高原丘陵区子午岭林地和开垦28年的侵蚀坡面为研究对象,分析土壤主要性质和养分含量的变化情况,运用经典统计学和地统计法分析坡面土壤基本性质和养分空间分布规律。林地开垦后坡面土壤pH增加了0.24个单位,有机质、全氮、全磷和铵态氮、硝态氮、速效磷和速效钾分别降低了13.77,1.14,0.10 g/kg和6.05,1.63,4.99,58.44 mg/kg。林地的土壤有机质、全氮和全磷的变异系数大于开垦地,而pH和各速效养分的变异系数小于开垦地。开垦后中坡位和下坡位养分含量减少幅度较大,上坡位减少幅度较小。林地和开垦地的土壤各指标都呈中等或强烈的空间自相关。林地开垦增强了有机质、全氮、全磷、铵态氮、速效磷和速效钾的空间异质性,但减小了pH的空间异质性,地形等结构性因子主导了土壤养分空间异质性的形成。林地开垦后,pH、有机质、全氮和全磷变程增大,铵态氮、硝态氮和速效钾变程减小,速效磷在2个坡面上的变化趋势不一致。研究结果表明林地开垦极大地减少了坡面土壤养分含量,但减少幅度与坡位和坡面形态有关。同时,开垦增大了坡面土壤有机质、全氮和全磷的空间依赖性,减小了速效养分的空间依赖性。     

植物篱对紫色土物理性质及养分的影响

在四川盆地紫色土区通过标准径流小区试验研究香根草植物篱对不同坡度的坡耕地表层(0-20cm)土壤容重、颗粒分布及养分流失的影响.结果表明,香根草植物篱有利于土壤容重减小,但总体上效果不显着.在植物篱的影响下,土壤细颗粒(粉粒、粘粒)在坡脚、坡腰明显富集,且总体上细颗粒流失减少,所以砂粒含量相对降低.香根草植物篱能有效控制表土各养分的流失,保持土壤肥力;能减少各养分在坡顶的流失,但全氮的流失依然严重;能加剧各养分在坡脚的富集,其中对有机质的影响最明显;能明显提高篱带前土壤肥力,尤其是总磷和速效钾含量.有机质、全氮、总磷、有效磷、速效钾的变化量分别与牯粒变化量呈显著线性正相关(r=0.859,0.896,0.821,0.807,0.927),与粉粒变化量相关性不强,所以它们在坡面上的变化趋势与粘粒基本一致.在植物篱小区,坡度对有机质、全氮、碱解氮、全钾的富集影响不明显,但坡度较小时,有效钾、坡顶碱解氮和坡顶有效磷的流失显著减少,所有小区坡面上的全钾含量均增加.因此,该区紫色土坡耕地要注意补充氮肥,减少钾肥,加强坡顶和远篱带处土壤的培肥.     

渝西丘陵区土地利用方式、景观位置对土壤养分的影响

运用实地调查与数理统计分析方法,研究了渝西丘陵区土地利用方式、景观位置对土壤有机质和氮磷钾养分的影响。结果表明,水田耕层土壤有机质、氮素和全钾含量显著高于旱作地类,菜地耕层土壤有效磷含量显著高于其他地类,各地类耕层土壤的全磷和速效钾含量无显著差异。不同景观位置下的耕层土壤有机质和氮素含量按冲沟、坡脚、平坝、坡腰、坡顶的顺序明显减少;全钾按冲沟、坡腰、坡顶、坡脚、平坝的顺序明显减少;坡脚、坡腰、冲沟部位耕层土壤速效钾显著高于坡顶、平坝;平坝、坡脚、坡腰部位耕层土壤有效磷显著高于冲沟、坡顶;各景观位置的耕层土壤全磷含量无显著差异。不同土地利用方式的土壤有机质和速效钾含量的剖面变化强弱程度是,园地菜地旱地;有效氮、磷则是菜地园地旱地。不同景观位置的土壤有机质含量的剖面变化强弱程度为,平坝坡脚坡腰坡顶;有效氮,平坝坡脚坡腰≈坡顶;有效磷,平坝坡脚坡腰≈坡顶;速效钾,坡顶坡脚坡腰平坝。     

采煤塌陷对风沙区土壤性质的影响

以毛乌素沙地东南缘大柳塔矿区为典型研究区,将灰色关联度模型引入土壤性质研究体系,对近20年陕北风沙区采煤塌陷造成的土壤性质变异性进行分析.结果表明：1）沉陷区坡中部位土壤含水量明显减小（P＜0.01）;坡中和坡顶部位土壤孔隙度增大（P＜0.05）;土壤粒级变粗;沉陷区土壤有机质和速效氮质量分数与未沉陷区相比差异显著（P＜0.01）;沉陷区土壤过氧化氢酶活性明显降低且在相当长的一段时间内不可修复（P＜0.01）.2）从不同土层深度上,风沙区采煤塌陷主要对表层（0 ～ 20 cm）土壤性质影响显著,对土壤养分的影响主要表现在碳和氮元素上,特别是不利于土壤中氮元素的保持与利用,同时塌陷裂缝和风蚀、水蚀作用加剧了土壤水分流失.     

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.     

Potential of wild species for genetic enhancement of some semi-arid food crops

Discovery and incorporation of genes from wild species provide means to sustain crop improvement, particularly when levels of resistance in the cultigens are low and virulent strains of pests and pathogens overcome the host plant resistance. The extent of utilization and the potential of the wild genepool for genetic enhancement were reviewed in five important food crops viz. sorghum, pearl millet, chickpea, pigeonpea and groundnut grown in the semi-arid tropics. Introgression from compatible wild germplasm in the primary gene pool resulted in transfer of new cytoplasmic male sterility systems in pearl millet and pigeonpea, development of high protein, cleistogamous flower and dwarf pigeonpea lines and foliar disease resistant groundnut cultivars. Utilization of wild species in secondary and tertiary gene pools has been generally limited due to sterility, restricted recombination or cross incompatibility. Nevertheless, these species are extremely important as they contain high levels of resistance to several important biotic and abiotic stresses. Several of them, like those belonging to the Parasorghum section and the rhizomatous Arachis species are sources of multiple resistances and hold great promise to sustain crop productivity.