南水北调与生态平衡

水是人类赖以生存繁衍的重要资源。我国人口逐年增长,而淡水资源数量有限。多变的自然降水及频繁的旱涝灾害,一直决定着我国农业收成乃至整个国民经济的盛衰。     

林农复合经营生态体系的研究

林农复合经营以生态经济学的原理,运用现代生物和生态工程方法技术,组成林、农、牧、副、渔有机结合的复合生产体系。它突破了传统林业的单一生产方式,形成以林为主的一个复合的、开放的、具有整体效应的生态系统。这种复合系统能有效地提高土地资源利用率,促进太阳能和有关物质在系统内的多次循环利用,实现整个系统在空间和时间上的高效利用。多年来的研究表明,这种由多种产业部     

The management of Insular Caribbean mangroves in relation to site location and community type

Mangrove ecosystems occupy different locations on Caribbean island coasts, ranging from open bays (fringe mangals) to totally enclosed salt ponds and salinas. On geomorphologically active coastlines, such as south Jamaica, systems are at varying degrees of maturity and productivity. Furthermore, because of system variability, the interactions between mangroves and associated marine systems, such as coral reefs and seagrass beds, are developed to different degrees.Community structure and productivity of a range of mangals on different islands of the Greater and Lesser Antilles are discussed. Forcing functions and levels of interaction with the marine environment are identified.The rational choice of management options must be based on the range of goods and services provided by the different systems; and a good understanding of their ecology is essential when choosing sites for protection, waste disposal, landfill, marina development and fisheries enhancement. Examples are given from current studies in Jamaica, St. Lucia, the British Virgin Islands and Trinidad, of a flexible management response to mangrove ecosystem diversity.     

Effects of legumes on soil physical quality in a maize crop

The effect of intercropped legumes and three N fertilizer rates in a continuous maize (Zea mays L.) cropping system on the physical properties of two soils were investigated for three years. The legumes, being a mixture of alfalfa, clover and hairy vetch, had a significant cumulative effect on some physical properties of both soil. The lowest stability and smallest mean weight diameter of soil aggregates were associated with monoculture maize plots. Aggregate size and stability were not affected by N fertilization at any of the rates of 0, 70, and 140 kg ha^-1 in intercropped plots, except that aggregate stability was actually reduced by N fertilization in one soil, the Ste. Rosalie clay. In maize plots in both soils, stability and size of soil aggregates were significantly increased with increased added N. Intercropped legumes significantly decreased dry bulk density and soil penetration resistance. Added N had no measurable influence on these compaction factors. Soil water properties were not significantly affected by either intercropping or N fertilization. Positive effects noted on soil aggregation and other physical properties in intercropped plots are the result of enhanced root activity, or incorporation of legumes as green manure, or both. Improvement of soil structure in maize plots associated with increasing N application was the result of increased maize-root residues.     

Genetic variability in the Arabian oryx (Oryx leucoryx)

An electrophoretic survey of blood markers of the Arabian oryx (Oryx leucoryx) was undertaken in order to ascertain the genetic variability in a sample of 85 individuals, mainly from Saudi Arabian (Taíf) and Jordanian herds. Three out of 18 loci were found to be polymorphic (P = 16.7%) and the mean heterozygosity (H = 0.052) appears to be relatively high with respect to the severe demographic bottlenecks expressed by the species since the 1960s. No genetic differentiation was found between Arabian and Jordanian samples considered. Consequences of these findings for the management of the Taíf herd and for such procedures as pedigree determination are discussed, and an example of this latter application is given for a case of doubtful parentage.     

Control of nematode parasites by grazing management—II. Decontamination of sheep and cattle pastures by varying periods of grazing with the alternate host

Commencing in December 1970, paddocks of a uniform series of sheep pastures were grazed for 6, 12 or 24 weeks by either yearling steers is or yearling ewes. Cattle pastures were treated similarly. All ewes and steers were pre-dosed with anthelmintic.At the conclusion of alternate grazing the effectiveness of the grazing treatments was evaluated by grazing each paddock for 1 month with either ten worm-free lambs (sheep pastures) or three wormfree calves (cattle pastures). The test animals were then slaughtered for total worm counts. The grazing of sheep pastures with cattle for 6, 12 or 24 weeks from December onwards resulted in reductions in numbers of Haemonchus contortus and Trichostrongylus colubriformis in test lambs. In comparison with continuous grazing by sheep, Nematodirus spp was only reduced after 24 weeks grazing by cattle. Cattle pastures grazed by sheep for 6 weeks showed no reduction in numbers of Ostertagia ostertagi or Cooperia oncophora in test calves. However after 12 weeks with sheep, numbers of O. ostertagi though not C. oncophora were reduced and after 24 weeks of alternate grazing both these species were reduced.Calves following the 6 week sheep treatments acquired both Haemonchus contortus and Trichostrongylus colubriformis and the calves from the 12 week sheep treatment paddock also carried H. contortus. For sheep the only evidence of cross-transmission was the occurrence of small numbers of Cooperia oncophora in test lambs from the 24 week cattle grazing treatment.The results provide evidence that sequential stocking with cattle and sheep in conjunction with anthelmintic treatment is an effective management strategy for preparing parasitologically safer pastures, but further information is required to determine the optimum timing of sequential stocking in farming situations.     

A global invasion by the thrip,Frankliniella occidentalis: Current virus vector status and its management

Western flower thrip, Frankliniella occidentalis (Pergande), is among the most economically important agricultural pests globally, attacking a wide range of vegetable and horticultural crops. In addition to causing extensive crop damage, the species is notorious for vectoring destructive plant viruses, mainly belonging to the genera Orthotospovirus, Ilarvirus, Alphacarmovirus and Machlomovirus. Once infected by orthotospoviruses, thrips can remain virulent throughout their lifespan and continue transmitting viruses to host plants when and wherever they feed. These irruptive viral outbreaks in crops will permanently disrupt functional integrated pest management systems, and typically require a remedial treatment involving insecticides, contributing to further development of insecticide resistance. To mitigate against this continuing cycle, the most effective management is early and comprehensive surveillance of the pest species and recognition of plant viruses in the field. This review provides information on the pest status of F. occidentalis, discusses the current global status of the viruses vectored by this thrip species, examines the mechanisms involved in transmitting virus‐induced diseases by thrips, and reviews different management strategies, highlighting the potential management tactics developed for various cropping systems. The early surveillance and the utilization of potential methods for control of both F. occidentalis and viruses are proposed.     

Quantifying the damage of red deer (Cervus elaphus) grazing on grassland production in southeastern Slovenia

The influence of red deer (Cervus elaphus) grazing on grassland production for forage conservation at the forest border during the vegetation period was studied on three locations (Mala gora, Cvišlerji, and Mačkovec) in the Kočevje region (SE Slovenia). The experiment lasted from the 25th of March until the 8th of October 2002. Portable cages were used to exclude red deer from grazing the herbage. At four sampling dates in the season, herbage air dry matter (DM) yield was measured at three different observations (cage-protected plot, cage-protected plot only two to three weeks before sampling date, otherwise freely grazed (removed), and unprotected plot). The results from the experiment showed that red deer grazed on grassland through the entire season and that the regeneration capability of sward was the highest in summer, middle in spring and smallest in autumn. On unprotected plots, an average reduction of 50% of herbage DM yield was found with the most damaged sites also up to 80% reduction.