Amelioration of a hardsetting Alfisol through deep mouldboard ploughing, gypsum application and double cropping. III. Crop production and profitability     

D.J.M. Hall  D.C. McKenzie  D.A. MacLeod  I.D. Toole 《Soil & Tillage Research》1994,28(3-4):287-300

Deep mouldoard ploughing to 0.45 m, gypsum application (5 t ha⁻¹), and double cropping were evaluated, alone and combined, as ameliorants for a hardsetting red-brown earth (Alfisol). The double cropped treatment consisted of winter wheat (Triticum aestivum) and a summer forage crop consisting of sudax (Sorghum sudanese) intersown with cowpea (Vigna unguiculata). This paper describes the effect of these treatments on crop development, yield, crop-water relations and economic returns. Crop emergence was not affected by any treatment. Mouldboard ploughing significantly increased wheat grain yield from 1.86 to 2.15 t ha⁻¹, in 1984, but not in 1985. Yield was also increased from 5.18 to 5.68 t ha⁻¹ as a result of gypsum addition in 1985—after no significant difference in 1984. Double cropping significantly increased yield (by 0.6 t ha⁻¹) in 1985. Greater increases were obtained with the summer cropping phase where higher evaporative demand during the summer would have aggravated soil structural problems associated with hardsetting. Sudax-cowpea dry matter yields were increased from 13.6 to 17 t ha⁻¹ and from 13.0 to 17.5 t ha⁻¹ during summer 1984–1985 by gypsum and mouldboard ploughing, respectively. The higher yields are attributed to increased water storage and depletion, and reduced soil strength for the mouldboard ploughed and gypsum main treatments. No interactions were found between the main treatments, except at the end of the 1985 winter cropping phase when there was a negative interaction between mouldboard ploughing and gypsum application for dry matter, equivalent root length and yield. The yield increases associated with mouldboard ploughing did not persist beyond the second year of the experiment. Double cropping combined with mouldboard ploughing (Mb+DC) was the most profitable treatment, whereas mouldboard ploughing with gypsum (Mb+G) was the least profitable for the crops grown in this experiment.  相似文献   

Inhibition of the complement cascade by the major secretory protein of vaccinia virus   总被引：28，自引：0，他引：28  

G J Kotwal  S N Isaacs  R McKenzie  M M Frank  B Moss 《Science (New York, N.Y.)》1990,250(4982):827-830

The complement system contributes to host defenses against invasion by infectious agents. A 35-kilodalton protein, encoded by vaccinia virus and secreted from infected cells, has sequence similarities to members of a gene family that includes complement control proteins. Biochemical and genetic studies showed that the viral protein binds to derivatives of the fourth component of complement and inhibits the classical complement cascade, suggesting that it serves as a defense molecule to help the virus evade the consequences of complement activation.  相似文献   

Venus volcanism: initial analysis from magellan data     

Head JW  Campbell DB  Elachi C  Guest JE  McKenzie DP  Saunders RS  Schaber GG  Schubert G 《Science (New York, N.Y.)》1991,252(5003):276-288

Magellan images confirm that volcanism is widespread and has been fimdamentally important in the formation and evolution of the crust of Venus. High-resolution imaging data reveal evidence for intrusion (dike formation and cryptodomes) and extrusion (a wide range of lava flows). Also observed are thousands of small shield volcanoes, larger edifices up to several hundred kilometers in diameter, massive outpourings of lavas, and local pyroclastic deposits. Although most features are consistent with basaltic compositions, a number of large pancake-like domes are morphologically similar to rhyolite-dacite domes on Earth. Flows and sinuous channels with lengths of many hundreds of kilometers suggest that extremely high effusion rates or very fluid magmas (perhaps komatiites) may be present. Volcanism is evident in various tectonic settings (coronae, linear extensional and compressional zones, mountain belts, upland rises, highland plateaus, and tesserae). Volcanic resurfacing rates appear to be low (less than 2 Km(3)/yr) but the significance of dike formation and intrusions, and the mode of crustal formation and loss remain to be established.  相似文献   

Spontaneous formation of macroscopic chiral domains in a fluid smectic phase of achiral molecules     

DR Link  G Natale  R Shao  JE Maclennan  NA Clark  E Korblova  DM Walba 《Science (New York, N.Y.)》1997,278(5345):1924-1927

A smectic liquid-crystal phase made from achiral molecules with bent cores was found to have fluid layers that exhibit two spontaneous symmetry-breaking instabilities: polar molecular orientational ordering about the layer normal and molecular tilt. These instabilities combine to form a chiral layer structure with a handedness that depends on the sign of the tilt. The bulk states are either antiferroelectric-racemic, with the layer polar direction and handedness alternating in sign from layer to layer, or antiferroelectric-chiral, which is of uniform layer handedness. Both states exhibit an electric field-induced transition from antiferroelectric to ferroelectric.  相似文献   

Biogeochemistry. Sulfate reducers--dominant players in a low-oxygen world?     

Vasconcelos C  McKenzie JA 《Science (New York, N.Y.)》2000,290(5497):1711-1712

Sulfate reducing bacteria can adapt to extreme physical and chemical conditions and play an important role in global geochemical cycles, but their role in the formation of ore deposits has remained controversial. Strong support for such a role is provided by Labrenz et al., who have discovered sulfate-reducing bacteria that can tolerate low levels of oxygen and can precipitate zinc sulfide minerals. The results may have implications for bioremediation and may provide clues to processes that may have been more widespread in the geologic past.  相似文献   

Lead, cadmium, and fluoride levels in market milk and infant formulas in Canada   总被引：2，自引：0，他引：2  

R W Dabeka  A D McKenzie 《Journal of the Association of Official Analytical Chemists》1987,70(4):754-757

Lead, cadmium, and fluoride were determined in 68 samples of market milk and about 115 infant formulas. Mean and median levels (ranges) in ng/g found for cow milk were as follows: lead, 1.12, 1.19 (0.01-2.48); cadmium, 0.10, 0.039 (0.005-0.74); and fluoride, 41, 40 (7-86). In canned, ready-to-use formulas, lead, cadmium, and fluoride levels averaged 37.3, 1.50, and 840 ng/g, respectively. In concentrated liquid formulas, the respective levels were 21, 3.54, and 600 ng/g. In powder formula concentrates, respective levels were 73.7, 6.78, and 1130 ng/g. On the basis of this study and literature data, lead levels in market milk exceeding 5 ng/g appeared to signify contamination of the milk either directly or via the cow. For formulas considered on an as-consumed basis, lead levels exceeding about 10-15 ng/g were attributed to contamination from either the can used to store the formula or the formula ingredients. Infant formulas in lead-free cans contained about 1.7 ng/g of lead on a ready-to-use basis. Milk-based formulas contained about 0.26 ng/g of cadmium on a ready-to-use basis. Soy-based or milk-free formulas contained about 8-15 times more cadmium than did milk-based formulas. Canadian and U.S. ready-to-use formulas contained 900 and 230 ng/g fluoride, respectively, and this difference was attributed to the level of fluoride in the processing water used by the manufacturers.  相似文献   

Calving rates in a tropical beef herd after treatment with a synthetic progestagen, norgestomet, or a prostaglandin analogue, cloprostenol     

JE FRISCH  CJ O'NEILL 《Australian veterinary journal》1996,73(3):98-102

Maiden heifers and lactating cows of known ovarian status and of several breeds were treated with a synthetic prostaglandin, cloprostenol, or a synthetic progestagen, norgestomet, at the start of an artificial insemination (AI) program. Animals in the cloprostenol treatment received 2 injections 10 days apart. Over the next 26 days those animals that showed oestrous behaviour were inseminated. Synchronisation rates and calving rates to insemination over the first 7 days were calculated. Those in the norgestomet treatment received an implant of norgestomet plus an injection of norgestomet and oestradiol valerate. The implant was removed 10 days later and the animals were given an injection of pregnant mare serum gonadotrophin (PMSG). They were inseminated at 48 h (maiden heifers) or 56 h (lactating cows) after implant removal. Calving rates to fixed-time insemination were recorded. After completion of the AI program the animals in both treatments were joined with bulls. Overall calving rates (AI plus bulls) were calculated. By day 7 of the program, 82% of the maiden heifers and 76% of the lactating cows in the cloprostenol treatment had been detected in oestrus. By day 21 the respective figures were 99% and 81% Norgestomet treatment had an immediate and a prolonged effect on ovarian activity in those females classified as having inactive ovaries at the start of the AI program. Calving rates of those females to fixed-time AI and overall were similar to those of the females with active ovaries in both treatments. Their calving rates to fixed-time insemination, and overall calving rates for the lactating females, were significantly higher than the corresponding values of their contemporaries treated with cloprostenol and inseminated on observed oestrus over 7 days. For those females classified as having active ovaries at the start of the AI program, calving rates to first insemination and overall were similar for both treatments. Overall calving rates of lactating cows of each breed were, with one exception, higher in the norgestomet treatment than in the cloprostenol treatment. Although norgestomet treatment was more expensive than cloprostenol treatment, the advantage in calf crop resulted in an overall monetary advantage to the norgestomet treatment.  相似文献   

The effect of artificial photoperiod at the end of the breeding season on plasma testosterone concentrations in stallions     

JE COX  PH REDHEAD†  NMA JAWADS‡ 《Australian veterinary journal》1988,65(8):239-241

Testosterone concentrations in stallions showed a seasonal trend with peak concentrations in the spring (April and May in Britain) and lowest concentrations in the period from December to February. The effect on this pattern of changing the length of the photoperiod at the end of the normal breeding season (mid-summer's day) was studied in 2 experiments. In the first experiment artificial illumination was organised from 21 June to mimic the effect of transfer to a southern hemisphere spring and summer, that is short days becoming longer. The stallions had low concentrations of testosterone in February and high concentrations in April. Concentrations in July, August and September were extremely low with a return to high values in late November/early December. In the second experiment, illumination was maintained at the equivalent of a 16 1/2-hour day from 21 June to mid December. These stallions had high testosterone concentrations in April, after which they fell until August, later rising to a maximum in October. These results are discussed in relation to transfer of stallions between the northern and southern hemispheres.  相似文献   

Intraruminal controlled release of cyromazine for the prevention of Lucilia cuprina myiasis in sheep     

N Anderson  J A McKenzie  R H Laby  M B Strong  R G Jarrett 《Research in veterinary science》1989,46(2):131-138

The efficacy of cyromazine, continuously released from intraruminal capsules at dose rates from 0.5 to 2 mg kg-1 d-1, was evaluated against implants of eggs and first instar larvae of Lucilia cuprina on Merino sheep. Estimates from the non-linear relationship between the success of implants and plasma concentrations showed that 95 per cent protection of sheep could be achieved at a mean release rate of 1.39 mg kg-1 d-1 cyromazine which gave rise to a mean plasma concentration of 0.26 mg litre-1. Present formulations allowed protection for about 90 days in a 40 kg sheep. The 'square wave' type of release profile provided negligible suboptimal dosing thus limiting the potential for selection of resistance. Systemic application of cyromazine provides control of covert and overt strike among sheep and could be used in ecologically based strategies for the control of L. cuprina populations.  相似文献   

Aetiology and Endocrinology of Pseudopregnancy in the Goat     

MAM Taverne  JW Hesselink    MM Bevers  HA van  Oord JE Kornalijnslijper 《Reproduction in domestic animals》1995,30(4):228-230

  相似文献