粤西地区三种不同土壤上的热带绿肥牧草引种试验

我国热带地区具有高温多雨、雨量分布不均匀且多暴雨的特点,容易引起水土流失,土壤有机质分解快,养分淋溶流失强烈,因此热带地区的红壤和砖红壤的有机质和速效养分含量都很低。热带经济林木和果园间种绿肥覆盖作物可以保持水土,增进地力,促使主作物速生高产^[1,2],而建立牧草基地以发展畜牧业和种植绿肥是增加优质有机肥料来源的有效途径。这样才有可能增施大量有机肥料,不断提高土壤肥力,保证农林作物稳产高产。     

Hillslope Evolution by Bedrock Landslides

Bedrock landsliding is a dominant geomorphic process in a number of high-relief landscapes, yet is neglected in landscape evolution models. A physical model of sliding in beans is presented, in which incremental lowering of one wall simulates baselevel fall and generates slides. Frequent small slides produce irregular hillslopes, on which steep toes and head scarps persist until being cleared by infrequent large slides. These steep segments are observed on hillslopes in high-relief landscapes and have been interpreted as evidence for increases in tectonic or climatic process rates. In certain cases, they may instead reflect normal hillslope evolution by landsliding.     

Yolk and serum cholesterol and production traits,as affected by incorporatinga supraoptimal amount of copper in the diet of the leghorn hen

1. An experiment was conducted to investigate the possibility of lowering the yolk cholesterol of the egg by supplementing the diet with supraoptimal amounts of copper (50, 150 or 250 mg/kg) as sulphate or acetate. 2. A significant reduction in egg production and a negative effect on food conversion was found when 250 mg/kg of copper was added compared to the control (no added copper). Acetate seemed significantly less harmful in both cases. 3. A significant linear reduction was found in plasma and yolk cholesterol (20% and 14%) and in plasma and yolk triglycerides (24% and 30%) as the dietary copper content was increased from 0 to 250 mg/kg. 4. Regardless of type or quantity of copper, cholesterol and lipids were decreased linearly as birds remained longer on the treatments. A significant interaction between quantity and period showed a greater reduction at a later time. 5. If slightly lower egg production can be accepted, the addition of 250 mg/kg copper might be beneficial in reducing the cholesterol content of the yolk.     

Tick transmission of Anaplasma centrale

Anaplasma centrale was isolated from a field collection of Rhipicephalus simus. Transstadial transmission of A. centrale with adult ticks was demonstrated, but the infection was not carried transovarially. Ticks from this collection were subsequently reared as a non-infected, laboratory strain. It was proved that the Onderstepoort live blood vaccine strain of A. centrale, isolated by Theiler in 1911, is still tick transmissible after more than 75 years of needle passage through cattle in the laboratory. Attempts to demonstrate transstadial transmission of the vaccine strain with Boophilus decoloratus and Boophilus microplus failed.     

Analysis of ruminant respiratory syncytial virus isolates by RNAse protection of the G glycoprotein transcripts.

Two different respiratory syncytial virus (RSV) radiolabeled probes were used to characterize the genetic heterogeneity of 25 ruminant RSV isolates by the ribonuclease protection assay. A 32P-radiolabeled antisense RNA probe was transcribed from cloned ovine and bovine RSV G glycoprotein genes and then hybridized with total RNA isolated from infected cells with various ruminant RSV isolates. The results of this study, along with previously published nucleotide sequence data of the ovine RSV G glycoprotein gene, suggest the presence of at least 2 ruminant RSV subgroups. One subgroup is represented by RSV isolated from respiratory disease outbreaks from calves and goats, and the other is represented by RSV isolated from sheep.     

Prevalence of bluetongue virus antibodies in sheep in central Ethiopia

Competitive ELISA was applied to detect antibodies against bluetongue virus in sheep sera collected from different agro-climatic areas in Ethiopia. A total of 90 serum samples were tested and 42 (46.67%) were positive for bluetongue virus antibodies. A prevalence rate ranging from 9.67% for sheep sampled in the highland to 92.85% for sheep sampled in the lowland was recorded. The prevalence correlated with the probable distribution of the Culicoides vector. This is the first report indicating the presence of bluetongue virus infection in animals from Ethiopia.     

Fire behaviour in the Kruger National Park

Abstract

Fire research in the Kruger National Park has largely been focussed on the effect of the season and frequency of burning on the vegetation. Very little information is available on the effect of fire behaviour and in particular fire intensity, on the flora of the Park. Consequently a research project was conducted to develop statistical models for predicting fire intensity, flame height and rate of spread in the field. The devleopment of these models constitutes the initial phase of determining the relationship between fire behaviour and vegetation response.     

A CASE ASSESSMENT OF THE MECHANISMS INVOLVED IN HUMAN‐INDUCED LAND DEGRADATION IN NORTHEASTERN KUWAIT

Soil degradation and vegetation deterioration in contrasting areas (open desert versus protected desert) in the northeastern part of Kuwait were investigated, using field measurements, and laboratory methodologies. The average infiltration rate of compacted soils studied was found to be 52 per cent lower than that of the undisturbed soils we investigated. The bulk density of the compacted soils was 19 per cent higher than that of the non‐compacted soils. The average topsoil resistance of severely compacted soils was 13 per cent greater than that of undisturbed soils and is mainly due to overgrazing, and off‐road vehicle use. We found that the overall vegetation cover status of open areas investigated was approximately 70 per cent less than for the protected areas studied. As a consequence of soil compaction and vegetation deterioration, sand deflation processes, and sand movement prevail in open areas. The total average percentages of course grain sizes in unprotected soils and heavily disturbed soils by vehicles (off‐road) are 51 and 103 per cent greater, respectively. The annual rate of sand transport during the last 20 years, from the prevailing wind direction (NW) in the area has increased by 81 per cent. The delicate balance between soil and natural vegetation cover is easily disturbed by off‐road vehicle use associated with overgrazing and recreation activity. A restoration plan is needed in order to reduce land degradation and to allow natural vegetation recovery. Copyright © 2011 John Wiley & Sons, Ltd.