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51.
Using a previous model as a base, data derived in field trials in wheat ( Triticum aestivuort L.) and bailey ( Hordeum vulgare L.) were assessed to estimate the yield penalty, and resulting reduction in economic benefit, from progressive spraying of herbicides up to late crop tillering. Compared with early post-emergence application, yield penalties from delayed spraying began at early tillering. For median values of weed-free yield and weed density in the data set. the loss in potential yield increase when spraying at late tillering compared with early post-emergence was 71%, Crops with higher weed-free yield potential and with greater initial weed density showed a proportionately (as well as absolutely) larger yield penalty from a moderate delay in spraying, indicating an earlier and more intense onset of competition with weeds. 相似文献
52.
BLACK DM 《Science (New York, N.Y.)》1953,118(3063):308-309
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TH Jones LJ Thompson JH Lawton TM Bezemer RD Bardgett TM Blackburn KD Bruce PF Cannon GS Hall SE Hartley G Howson CG Jones C Kampichler E Kandeler DA Ritchie 《Science (New York, N.Y.)》1998,280(5362):441-443
In model terrestrial ecosystems maintained for three plant generations at elevated concentrations of atmospheric carbon dioxide, increases in photosynthetically fixed carbon were allocated below ground, raising concentrations of dissolved organic carbon in soil. These effects were then transmitted up the decomposer food chain. Soil microbial biomass was unaffected, but the composition of soil fungal species changed, with increases in rates of cellulose decomposition. There were also changes in the abundance and species composition of Collembola, fungal-feeding arthropods. These results have implications for long-term feedback processes in soil ecosystems that are subject to rising global atmospheric carbon dioxide concentrations. 相似文献
54.
BRYAN A. BLACK ROBERT J. ALLMAN ISAAC D. SCHROEDER MICHAEL J. SCHIRRIPA 《Fisheries Oceanography》2011,20(5):347-356
Dendrochronology (tree‐ring analysis) techniques were applied to develop chronologies from the annual growth‐increment widths of red snapper (Lutjanus campechanus) and gray snapper (Lutjanus griseus) otoliths sampled from the northern Gulf of Mexico, USA. Growth increment widths showed considerable synchrony within and across species, indicating that some component of environmental variability influenced growth. The final, exactly dated red snapper chronology continuously spanned 1975 through 2003, while the gray snapper chronology continuously spanned 1975 through 2006. To determine baseline climate‐growth relationships, chronologies were compared to monthly averages of sea surface temperatures, U winds (west to east), V winds (south to north), and Mississippi River discharge. The gray snapper chronology significantly (P < 0.01) correlated with winds and temperature in March and April, while the red snapper chronology correlated with winds in March. Principal components regression including springtime winds and temperature accounted for 28 and 52% of the variance in the red and gray snapper chronologies, respectively. These results indicate that snapper growth was favored by warm sea surface temperatures and onshore winds from the southeast to the northwest in March and April. Overall, this study provides preliminary, baseline information regarding the association between climate and growth for these commercially important snapper species. 相似文献
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PF LEWIS 《Australian veterinary journal》1994,71(5):130-132
SUMMARY Common tiger snake (Notechis scutatus) venom was injected into mice and dogs at various dose rates calculated on the known lethal dose (LD) for each species. The larger the dose of venom, the earlier was the onset of clinical signs and the more rapid and severe the course of the disease in both species. In dogs injected with 32 LD of venom, there was sudden collapse and death in about one hour from the time of injection without recovery from premonitory depression and before mydriasis occurred. Dogs given 5 to 16 LD of venom developed preparalytic signs (vomition, salivation or defaecation) in 5 to 30 min, mydriasis in 2 to 4h, became paralysed and died in about 2.5 to 5 h. When doses of venom of about 1 LD were injected, vomition and salivation occurred within 2 h and mydriasis in about 4 h. The dogs were unable to close the mouth completely despite retention of jaw muscle tone. At the site of injection of venom there was occasional but slight erythema and oedema. Sublethally envenomed dogs did not show preparalytic signs nor did they have general skeletal muscle paralysis. Even at the lowest dose tested (0.25 LD), however, they developed mydriasis and photophobia, which persisted for several days. 相似文献
58.
Objective To assess the persistent activity of injectable formulations of abamectin and doramectin against gastrointestinal nematodes of cattle.
Design Controlled slaughter study assessing residual efficacy.
Procedure Nematode-free calves were treated with abamectin or doramectin (each at a dose of 200 μg/kg) and infections then induced with repeated doses of infective larvae of Trichostrongylus axei, Haemonchus placei, Ostertagia ostertagi and Cooperia species. The duration of challenge ranged from 14 to 28 days. The calves were slaughtered at either 38/39 or 45/46 days after the treatments and nematodes recovered from the gastro-intestinal tract.
Results Significant reductions in numbers of O ostertagi occurred for both abamectin and doramectin treatments (> 93%) relative to counts in untreated calves, when challenge was administered up to 21 days after treatment. For T axei and Cooperia spp significant reductions occurred when the challenge occurred for 14 days after treatment (99%). Although differences from untreated animals were not significant, the results for H placei suggested high efficacy (> 85%) for up to 21 days for doramectin and up to 28 days for abamectin.
Conclusion There was no significant difference between abamectin and doramectin for any parasite at any challenge point, indicating that there is equivalent persistent activity of doramectin and abamectin against important gastrointestinal nematodes of cattle. 相似文献
Design Controlled slaughter study assessing residual efficacy.
Procedure Nematode-free calves were treated with abamectin or doramectin (each at a dose of 200 μg/kg) and infections then induced with repeated doses of infective larvae of Trichostrongylus axei, Haemonchus placei, Ostertagia ostertagi and Cooperia species. The duration of challenge ranged from 14 to 28 days. The calves were slaughtered at either 38/39 or 45/46 days after the treatments and nematodes recovered from the gastro-intestinal tract.
Results Significant reductions in numbers of O ostertagi occurred for both abamectin and doramectin treatments (> 93%) relative to counts in untreated calves, when challenge was administered up to 21 days after treatment. For T axei and Cooperia spp significant reductions occurred when the challenge occurred for 14 days after treatment (99%). Although differences from untreated animals were not significant, the results for H placei suggested high efficacy (> 85%) for up to 21 days for doramectin and up to 28 days for abamectin.
Conclusion There was no significant difference between abamectin and doramectin for any parasite at any challenge point, indicating that there is equivalent persistent activity of doramectin and abamectin against important gastrointestinal nematodes of cattle. 相似文献
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PF LEWIS 《Australian veterinary journal》1994,71(5):136-139
SUMMARY The myotoxicity and neurotoxicity of common tiger snake (Notechis scutatus) venom are major factors in the pathogenesis of envenomation in the dog. Histological examination of the tissues of experimentally envenomed dogs has demonstrated the importance of muscle damage in affecting the clinical syndrome of tiger snake envenomation. Within one hour of injection of the venom into dogs, there was selective involvement of some muscles. Cardiac and smooth muscles were not significantly affected. The severity of myofibre damage was influenced by the amount of venom injected. Immobilisation under general anaesthesia resulted in significant protection against the myotoxic effects of high doses of venom. Lesions in the kidneys of experimentally envenomed dogs were acute tubular necrosis and the variable presence of a small amount of proteinaceous material in tubules. These lesions, which were similar to those in cases of natural snake bite, were indicative of a direct nephrotoxic effect, which could be complicated by the effects of myoglobinuria. These findings emphasise the need for supportive treatment aimed at maintenance of renal function in the treatment of dogs suffering from tiger snake envenomation. 相似文献