Assessing the compaction susceptibility of South African forestry soils. II. Soil properties affecting compactibility and compressibility     

C. W. Smith  M. A. Johnston  S. Lorentz 《Soil & Tillage Research》1997,43(3-4)

Factors affecting the compaction susceptibility of South African forestry soils were assessed. Two traditional measures of compaction susceptibility were used: maximum bulk density (ρ_mbd) determined by the standard Proctor test, defined compactibility, and the compression index using a simple uni-axial test, defined compressibility. Soils were chosen from a broad range of geological and climatic regions and they varied greatly in texture (8 to 66 g 100 g⁻¹ clay) and organic matter content (0.26 to 5.77 g 100 g⁻¹ organic carbon). Soils showed a wide range in ρ_mbd values, from 1.24 to 2.00 Mg m⁻³, and this reflected the wide range of particle size distributions and organic matter contents of the soils. Very good correlations were achieved between measures of particle size distribution, particularly clay plus silt and both compactibility and compressibility. Both compactibility and compressibility were significantly correlated with loss-on-ignition (L_OI) which is a measure reflecting the combined effects of soil texture and organic matter on soil physical properties. Indices of compaction susceptibility were influenced more by particle size distribution than by organic carbon content. Clear effects of organic carbon on compaction behaviour were only evident for soils with low clay contents (< 25 g 100 g⁻¹. No clear relationship between compactibility and compressibility was found. Compactibility generally increased with decreasing clay plus silt content, whereas compressibility increased up to about 70 g 100 g⁻¹ clay plus silt before decreasing again. It is difficult to define compaction susceptibility solely in terms of indices of compactibility or compressibility particularly as there is no clear relationship between these two properties. A classification system for compaction risk assessment is presented, based on the relationship between compactibility (ρ_mbd) and L_OI, and between clay plus silt content and compressibility.  相似文献   

Dry bean production with various tillage and residue management systems     

Edward J. Deibert 《Soil & Tillage Research》1995,36(3-4):97-109

Limited information is available on the influence of high surface residue tillag systems and the interaction of weed control methods, cultivar maturity, and phosphorus fertilizer placement on yield parameters of dry bean (Phaseolus vulgaris L.) A 3-year field study was conducted on a Fargo clay (fine, frigid, montmorillonitic Vertic Haplaquoll) to evaluate the influence of surface or deep band placed phosphorus fertilizer, tillage systems (PLOW, SWEEP, STRIP, NOTILL) and weed control methods on harvest plant populations, seed yield and seed weight of ‘Upland’ (early maturity) and ‘C-20’ (late maturity) dry bean cultivars. Yield variables were influenced by cultivar planted and climatic conditions. Zinc deficient plants and decreased yield were observed with the ‘C-20’ cultivar when grown on PLOW system plots where phosphorus fertilizer was surface applied. Zinc deficient plants were not present when the phosphorus fertilizer was deep banded or none was applied. No zinc deficient plants were observed on NOTILL, STRIP and SWEEP system plots. Both cultivars matured 7 to 10 days earlier with NOTILL, STRIP and SWEEP systems when compared with the PLOW system. Dry bean yields were reduced 180 to 310 kg ha⁻¹ by cultivation for weed control. Little difference in yields occurred among tillage systems when climatic conditions were normal. During a cool wet season, seed yields on PLOW system plots were 150 to 400 kg ha⁻¹ higher than on plots of systems with surface residue. Seed weight, although lower on the late maturity cultivar, was not greatly changed by tillage or weed control method. Results from this study indicate that dry beans can be successfully grown with small grain surface residue systems in northern climatic areas where growing degree days exceed 1200 and growing season precipitation does not exceed 400 mm. Further, deep band placement of phosphorus fertilizer is essential in dry bean rotations to eliminate potential zinc deficiency on soils low in zinc. Switching to a high residue management system may require a special cultivator design to eliminate yield loss due to pruning of shallow roots present with high surface residue.  相似文献   

Yield and N uptake as affected by soil tillage and catch crop     

E.Møller Hansen  J. Djurhuus 《Soil & Tillage Research》1997,42(4):241-252

Two field trials with spring barley (Hordeum vulgare L.) were conducted at two locations in Denmark in order to evaluate the effects of tillage and growth of a catch crop on yield parameters under temperate coastal climate conditions. Ploughing in autumn or spring in combination with perennial ryegrass (Lolium perenne L.) as a catch crop was evaluated on a coarse sand (Orthic Haplohumod) from 1987 to 1992 at three rates of N fertiliser application (60, 90 and 120 kg N ha⁻¹ year⁻¹). Rotovating and direct drilling were also included as additional tillage practices. The experiment was conducted on a 19-year-old field trial with continuous production of spring barley. Ploughing in autumn or spring in combination with stubble cultivation and a catch crop, in addition to minimum tillage, was evaluated in a newly established field trial on a sandy loam (Typic Agrudalf) from 1988 to 1992. Yield parameters and N concentrations in grain and straw were determined. On the coarse sand, N uptake in the grain in ploughed plots without a catch crop was significantly greater when spring ploughed as opposed to autumn ploughed, but grain and straw yields did not differ significantly. Grain yield, straw yield and total N uptake did not differ significantly between direct drilled and autumn ploughed plots, but the trend was for grain yield to be lower with direct drilling. After 19 years of catch crop use, yield parameters in ploughed plots were greater than in plots without catch crops. This was most pronounced in the autumn ploughed plots. Rotovating the catch crop in the spring decreased grain yield compared with underploughing the catch crop in autumn or spring. No significant interactions were found between tillage and N rates. On the sandy loam, grain as well as straw yield and total N uptake were not significantly affected by catch crop or time of ploughing. Grain yield was significantly lower with reduced tillage (stubble cultivation in autumn) than in all other treatments.  相似文献   

Conservation tillage systems, fungal complexes and disease development in soybean and barley rhizospheres in Prince Edward Island     

A. V. Sturz  M. R. Carter 《Soil & Tillage Research》1995,34(4):225-238

A potential for reduced soil macroporosity (below 12% soil volume) under direct drilling, with a concomitant increase in soil relative saturation, is associated with an increase in crown and root rots in Prince Edward Island field crops. Four long-term tillage systems (moldboard plowing, paraplowing-direct drilling, rotary cultivation and direct drilling) were compared in relation to the pathogenic fungal complexes formed in a two crop rotation in spring barley (Hordeum vulgare L.) and soybean (Glycine max L. Merrill) over a 3 year period in a cool humid region of eastern Canada. The principal phytopathogenic fungal complex of Rhizoctonia solani Kühn, Fusarium avenaceum (Fr.) Sacc. and F. oxysporum Schl. remained constant over the treatments. Tillage practice did not affect the number of colony forming units of R. solani in the rhizosphere. The recovery of R. solani from root tissues tended to be lower following conservation tillage and was attributed to antagonism associated with elevated numbers of saprophytic trash microflora concentrated at the soil surface. Disease levels in potato (Solanum tuberosum L.) plantlet bioassays were not influenced significantly by soil source or tillage regime. However, plantlet growth tended to be depressed following transplantation into soil from soybean plots in 1993. Under optimum soil physical conditions conservation tillage did not appear to influence disease levels in barley and soybean rotations.  相似文献   

Effect of soil macroporosity and aggregate size on seed-soil contact     

A. D. Brown  A. R. Dexter  W. C. T. Chamen  G. Spoor 《Soil & Tillage Research》1996,38(3-4):203-216

The influence of soil structure on the degree of seed-soil contact within a seedbed is poorly understood. This paper presents a simple analogue of seed-soil contact which allows the examination of the influence of macroporosity and relative aggregate size on the degree of contact within a bed of deformable spheres. A method is described in which a rigid disc or sphere representing a seed is placed within a bed of deformable spheres of uniform size representing soil aggregates. The structure is then compressed uniaxially to a given macroporosity. Contact areas were measured by a technique involving the use of paint, dismantling of the sample, and image analysis. Results show that degree of contact increases as macroporosity decreases. Greatest levels of contact are achieved where rigid and deformable spheres are of similar size. This result appears to be a consequence of maximum stress concentration occurring at this size ratio. Contact points were unevenly distributed over the surface of the rigid sphere. The applicability of these findings is considered.  相似文献   

Serotypes of Escherichia coli strains isolated from piglets with diarrhea in swine industrial farms     

D. Ciosek  M. Truszczy&#x;ski 《Comparative immunology, microbiology and infectious diseases》1982,5(4):405-412

Serotypes of E. coli strains isolated from piglets, which died with symptoms of diarrhea in 9 swine industrial farms, were determined. Large numbers of serotypes (from 16 to 27) in individual farms were detected. The sets of serotypes from 9 investigated farms differed among each other significantly, depending on the farm and time of examination. It was found that more than one serotype of E. coli may exist in the pig body and contribute to the development of disease. The predominant serotypes, i.e. those comprising more than 10% of serologically determined strains, were found to exist in 6 of the investigated farms and not in the remaining ones. Among the predominant serotypes, particularly important seem to be strains with K88 antigen. For prophylaxis of piglet colibacteriosis in industrial farms in Poland two vaccines for sows are recommended: one containing the K88 antigen only and the other the following serotypes: 0149:K91,K88; 020:K57; 020:K83; 0157:K88; 01:K1; 0136:K78; 024:K?; 078:K80 and 0118:K? Strains belonging to these serotypes were the most prevalent in our strain collection.  相似文献   

Development of a leukocytopenic baby guinea pig model with azathioprine and cyclophosphamide     

Ashir Kumar  Mark C. Leonard  Ronald P. Cleveland 《Comparative immunology, microbiology and infectious diseases》1989,12(4):91-94

Immunosuppressive agents were given to baby guinea pigs to develop a leukocytopenic baby guinea pig model. Azathioprine in different doses, and cyclophosamide and methylprednisolone combinations did not result in predictable leukocytopenia without significant mortality. A combination of azathioprine 20mg and cyclophosphamide 20mg administered once daily for 5 days to 42 baby guinea pigs resulted in a mean white blood cell count of 2531/mm³ ±1198 (a reduction of 3931 ± 1413 from pretreatment values). The mean counts for polymorphonuclear leukocytes and lymphocytes on day 6 were 398/mm³ and 2035/mm³, respectively. Only 7% mortality was seen in these animals. This model can be utilized to study a variety of bacterial and viral infections in “immunocompromised hosts”.  相似文献   

Affinity of microorganisms of the genus Ureaplasma to the reproductive organs of cattle     

J Pilaszek  M Truszczyński 《Comparative immunology, microbiology and infectious diseases》1988,11(3-4):177-180

The purpose of this work was to define more precisely the role of Ureaplasma organisms in the aetiology of granular vulvovaginitis and balanoposthitis (GVVBP) of cattle. To contribute to this question the frequency and degree of infection with Ureaplasmas in two main groups of cattle was taken into account: (a) in cattle with symptoms of the mentioned disease, (b) in cattle without clinical symptoms. The samples of semen from 301 sires with symptoms of GVVBP and from 43 healthy sires as also vaginal mucus swabs from 96 cows with GVVBP and from 40 cows mated by the sire infected with Ureaplasma organisms and from 50 cows inseminated with semen which contained Ureaplasma organisms were taken for bacteriological examinations. The control group in relation to the above mentioned cows constituted of 22 heifers free from symptoms of GVVBP and neither inseminated nor mated naturally. It has been shown that on an average 78.1% of sires with pathological changes in the mucosa of the penis or prepuce and only 25.6% of healthy sires were infected with Ureaplasma organisms. The concentration of Ureaplasma organisms was also significantly higher in material obtained from sires with symptoms of the disease than in that from healthy animals. Ureaplasma organisms were demonstrated more frequently (72.7%) in cows with GVVBP than in cows without these symptoms (13.3%). Similarly, as in the material obtained from sires, in the material taken from cows with symptoms of the disease the concentration of Ureaplasma organisms was significantly higher than that in the material originating from the healthy cows. The obtained findings may indicate that Ureaplasma organisms play a role in the aetiology of GVVBP.  相似文献   

Experimental infection and cross protection tests in calves with cytopathic strains of bovine rotavirus     

G Castrucci  M Ferrari  F Frigeri  V Cilli  F Caleffi  V Aldrovandi  L Rampichini  F Tangucci 《Comparative immunology, microbiology and infectious diseases》1983,6(4):321-332

Four cytopathic strains (81/32F, 81/36F, 81/40F, 82/80F) of bovine rotavirus were shown to be pathogenic for conventionally reared newborn calves. Calves were infected orally, using 3 calves for each isolate. All became febrile, were depressed and diarrhoeic. Two calves, one of which in the group of those infected with 81/36F isolate, and the other infected with strain 81/40F, were killed when moribund. A 3rd calf from the 81/36F infected group, died. At necropsy localized lesions of the small intestines, which are considered to be typical of rotavirus infection, were found. Virus was consistently isolated from the fecal samples of the inoculated calves up to 13 days post-inoculation. It was speculated that some differences existed in the virulence of the bovine rotaviruses tested. The cross protection tests revealed that 1 strain (81/36F) might be antigenically more complex than the others.  相似文献   

Influence of sodium diethyldithiocarbamate (Imuthiol) on lymphocyte function and growth in weanling pigs     

K.P. Flaming  R.C. Thaler  F. Blecha  J.L. Nelssen 《Comparative immunology, microbiology and infectious diseases》1988,11(3-4):181-187

Mitogen-stimulated lymphocyte proliferation, delayed-type hypersensitivity (DTH) reactions, interleukin-2 (IL-2) production, and growth performance were evaluated in 3-week-old pigs treated with imuthiol. Lymphocyte proliferative responses to Con A and PWM were reduced (P < 0.05) in pigs treated with imuthiol at 25 mg/kg; PHA proliferative responses were not influenced by imuthiol treatment. Imuthiol at 2.5 mg/kg and 25 mg/kg lowered IL-2 production when compared to saline-treated controls. Delayed-type hypersensitivity responses to PHA were higher in 25 mg/kg imuthiol-treated pigs; however, 2.5 mg/kg imuthiol-treated pigs had lower DHT reactions. Imuthiol at 2.5 mg/kg and 25 mg/kg reduced (P < 0.05) average daily feed intake. These data suggest that in vivo imuthiol treatment in pigs lowers lymphocyte proliferative responses, IL-2 production, and growth performance.  相似文献