Oceanic Rossby waves acting as a "hay rake" for ecosystem floating by-products     

Dandonneau Y  Vega A  Loisel H  du Penhoat Y  Menkes C 《Science (New York, N.Y.)》2003,302(5650):1548-1551

Recent satellite observations of Rossby waves and chlorophyll anomalies propagating in subtropical gyres have suggested that wave-induced upwelling could stimulate photosynthesis. Instead, we show that chlorophyll maxima are located in abnormally warm water, in Rossby wave-induced convergences. This excludes inputs of nutrients from deeper water. We argue that the sea color anomalies are not caused by chlorophyll but by floating particles evolved from the ecosystem and accumulated by Rossby waves, acting as "marine hay rakes," in convergence zones. Such processes may be determinant for the distribution of living organisms in oligotrophic areas.  相似文献   

The Gold Standard of Dental Care : The Geriatric Horse     

Nicole du Toit  Bayard A. Rucker 《Veterinary Clinics of North America: Equine Practice》2013

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Identification and selection of benchmark sites on litholitic soils of the western grassland biome of South Africa     

O.J.H. Bosch  F.P. Janse van Rensburg  S. du T. Truter 《African Journal of Range and Forage Science》2013,30(2):59-62

Abstract

An approach to identify benchmarks for different ecological situations in the grassland biome is described. The approach is illustrated by using information on vegetation change, role of habitat factors and the relative palatability differences between the species of the vegetation on shallow soils of the litholitic complexes in the western parts of the grassland biome. The information was obtained from the ordination and interpretation of vegetation and habitat data gathered at different distances from watering points and in vegetation under different grazing pressures.  相似文献   

The national grazing strategy of the Republic of South Africa Objectives,achievements and future challenges     

P.F. du Toit  A.J. Aucamp  J.J. Bruwer 《African Journal of Range and Forage Science》2013,30(4):126-130

Over the past few years various measures have been applied to address the problem of the retrogression of southern African rangelands. However, it has become apparent that many of these measures were ad hoc and not part of a long‐term strategy aimed at fostering effective management of the rangeland resources. The White Paper on Agricultural Policy, tabled in May 1984, made reference to the alarming deterioration of natural rangelands and led to the drawing up of the National Grazing Strategy (NGS), released to Parliament in May 1985, which was endorsed by the Department of Agriculture and accepted in its entirety by the Government. The NGS committed authorities to reassess approaches to rangeland utilization in South Africa and to achieve a number of clearly‐defined goals within a specified time frame. The implementation of the NGS has been carefully monitored. Despite some progress, few of the goals set have actually been achieved. However, various problems have arisen such as the need to: encourage the cooperation of all range users, develop informed public opinion, increase manpower and establish priorities, all of which must be taken into account when future rangeland strategies are devised. These strategies also need to recognize the dichotomy that exists between programmes aimed at the development of certain industries and those aimed at resource conservation. It is proposed that future implementation of the NGS should be augmented by some of the following important second phase actions: (i) The strategy should be converted into a policy to be applied to all Departmental institutions, (ii) policy makers and politicians must accept liability and must take the lead in the application of stringent measures aimed at agricultural resource conservation and utilization.  相似文献   

JAARSVERSLAG VAN DIE UlTVOERENDE KOMITEE VAN DIE SUrDAFRIKAANSE BOSBOUVEREENIGING VIR DIE JAAR GEEINDIG MEI 31, 1964     

P. E. du PREEZ 《Southern Forests》2013,75(1)

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JAARSVERLAG VAN DIE UITVOERENDE KOMITEE VAN DIE SUID-AFRIKAANSE BOSBOUVERENIGING VIR DIE JAAR GEËINDIG MEI 31, 1960     

P. E. du Preez 《Southern Forests》2013,75(1)

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烟草青枯病菌的田间快速检测     

杜桂萍  肖启明 《湖南农业大学学报(自然科学版)》2010,36(2):192-195

用平板菌落计数法确定7种抗菌素对烟草青枯菌生长和抑制杂菌的最高浓度,通过正交试验确定药剂的最佳组合:安必仙9.996×10-5μg/mL、氧氟沙星9.990×10-7μg/mL、罗红霉素2.998×10-6μg/mL、头孢拉定3.000×10-6μg/mL、乙酰螺旋霉素1.998×10-5μg/mL、克拉霉素2.999×10-5μg/mL、阿奇霉素1.999×10-6μg/mL.利用以上最佳浓度配比的选择培养基检测湖南湘西、永州、郴州烟田土样中青枯菌,结果表明:湘西土样中青枯菌含量较大,永州次之,郴州相对较少,与青枯病发生的严重程度呈正相关,其中加青枯菌拮抗菌肥土壤中的含菌量明显少于未加菌肥土壤.  相似文献   

Intensive,site-specific silviculture: Manipulating resource availability at establishment for improved stand productivity. A review of South African research     

Ben du Toit  Colin W. Smith  Keith M. Little  Grant Boreham  Robert N. Pallett 《Forest Ecology and Management》2010

An important window of opportunity to increase and sustain productivity in short-rotation plantations is the period from felling through re-establishment to canopy closure. This paper explores the effects, interactions and response mechanisms of intensive silvicultural practices on plantation productivity and sustainability, using five South African case studies (a–e). (a) Land preparation trials showed that complete surface cultivation by ploughing had a significant beneficial effect when afforestation is done for the first time in grasslands, improving basal area growth by 11–52% over pitting only. However, similar treatments have not resulted in significant growth responses under re-establishment conditions. (b) Stand growth suppression resulting chiefly from soil compaction during mechanised harvesting operations is strongly related to soil type, soil textural class and residue management options. Volume growth reduction in short-rotation eucalypt crops ranged from 25% on compaction sensitive loamy soils to less than 2% in resistant sandy soils. (c) The response mechanism whereby vegetation management improves stand productivity is a reduction in both inter-specific and intra-genotypic competition for resources, as well as a decrease in stand variability. Operationally, the most important criteria in a vegetation management programme relate to the timing of control operations across diverse site conditions. In local trials, the primary factors controlling the time taken for competition-induced tree growth suppression to occur were related to altitude, slash burning and the interaction between these factors, which facilitated the development of regional vegetation management strategies. (d) Empirical fertilizer trials in short-rotation hardwood stands have shown significant improvements in final productivity (commonly 20–90 m³ ha⁻¹ in eucalypts and 30–50 m³ ha⁻¹ in Acacia), as well as wood density (15–30 kg m⁻³ for eucalypts) following improvements in early nutrition. Improved nutrition was achieved through fertilization at planting or indirectly through residue management. The response mechanism is primarily due to early canopy development and associated increases in light capture, coupled with a more modest increase in canopy quantum efficiency and above-ground carbon allocation on a dry site. On sites with abundant water supply, increased quantum efficiency is likely to be the dominant response mechanism. (e) A series of operational gains trials tested the interactive effect of genetic tree improvement, site–genotype interaction, stand density and vegetation management + fertilization on eucalypt stand growth across five sites. There were no significant interactions between factors, but importantly, the results were additive, emphasizing the need to optimise each practice in the value chain to achieve maximum productivity.  相似文献   

Determination of the cellulose and lignin content on wood fibre surfaces of eucalypts as a function of genotype and site     

A. Klash  E. Ncube  B. du Toit  M. Meincken 《European Journal of Forest Research》2010,129(4):741-748

We compared the chemical composition of wood fibres and fibre surfaces of several eucalypt species and hybrids originating from various growth sites in South Africa. The objective was to test for differences in chemical surface composition due to genetics or site with the ultimate aim to facilitate a tailor-made supply of wood for pulping that results in an optimal blend of fibres that can be pulped together with similar yields. This, however, requires a sound knowledge of the fibre properties. The surface functionality on the single fibre level is a key property, because it determines how good inter-fibre bonding will be when paper is formed, which depends amongst other fibre properties on the amount of free hydroxyl groups that are available and therefore on the cellulose content on the fibre surface. The cellulose and lignin content on the fibre surface were determined with chemical force microscopy, a variation of atomic force microscopy. Since the general bulk composition of the fibre and the surface composition might differ, both parameters were determined. We found significant differences in the cellulose and lignin content on fibre surfaces, with regard to genotype and site, respectively. In some, but not all, cases, the surface composition of wood fibres followed the bulk composition, and differences were generally more pronounced. Differences due to genotype were significant, especially with regard to the surface lignin content—but variation due to site was also distinctly recognisable. This variation in surface functionality could be the reason why some pulpwood blends result in a lower pulp yield and different quality.  相似文献   

韩国新村运动中的文化建设经验及启示   总被引：1，自引：1，他引：0  

杜丽华 《中国农学通报》2011,27(20):178-181

韩国在20世纪60年代组织实施的“新村运动”中,农村文化建设取得了巨大成功。文章总结了韩国新村运动中的文化建设经验：充分发挥政府的职能;重视农民的“精神启蒙”;注重农民的教育培训;注重村容环境的改观;政府给予财政支持等。指出中国当前在新农村文化建设中应该落实政府责任,发挥政府主导作用;重视农民教育,培养新型农民;创新农村人文生态环境,打造新村镇。  相似文献