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   

Soil acidification during more than 100 years under permanent grassland and woodland at Rothamsted   总被引：8，自引：0，他引：8  

A. E. Johnston  K. W. T. Goulding  P. R. Poulton 《Soil Use and Management》1986,2(1):3-10

Abstract Soil samples have been taken periodically from unlimed plots of the 130-year-old Park Grass Experiment and from the 100-year-old Geescroft Wilderness at Rothamsted. Changes in the pH of the samples show how acidification has progressed. The soils are now at, or are approaching, equilibrium pH values which depend on the acidifying inputs and on the buffering capacities of the soils. We have calculated the contributions to soil acidification of natural sources of acidity in the soil, atmospheric deposition, crop growth and nutrient removal, and, where applicable, additions of fertilizers. The relative importance of each source of acidification has changed as the soils have become more acid. Acid rain (wet deposited acidity) is a negligible source, but total atmospheric deposition may comprise up to 30% of acidifying inputs at near neutral soil pH values and more as soil pH decreases. Excepting fertilizers, the greatest causes of soil acidification at or near neutral pH values are the natural inputs of H⁺ from the dissolution of CO₂ and subsequent dissociation of carbonic acid, and the mineralization of organic matter. Under grassland, single superphosphate and small amounts of sodium and magnesium sulphates have had no effect on soil pH, whilst potassium sulphate increased soil acidity slightly. All of these effects are greatly outweighed under grassland, however, by those of nitrogen fertilizers. Against a background of acidification from atmospheric, crop and natural inputs, nitrogen applied as ammonium sulphate decreased soil pH up to a maximum of 1.2 units at a rate in direct proportion to the amount added, and nitrogen applied as sodium nitrate increased soil pH by between 0.5 and 1 unit.  相似文献   

Folate content in commercial white and whole wheat sandwich breads     

Johnston KE  Tamura T 《Journal of agricultural and food chemistry》2004,52(20):6338-6340

After the U.S. mandate of folic acid fortification of enriched grain products, a report indicated higher than expected fortification. Limited information is available on folic acid in enriched products. We measured the folate content in 92 sandwich breads (46 white breads and 46 whole wheat breads) in Birmingham, Alabama, during 2001-2003. The mean folate content in white bread declined significantly from 2001 to 2002 or 2003, whereas the decline in folate content in whole wheat bread containing enriched flour was not significant. White bread contained significantly more folate than whole wheat bread containing enriched flour in 2001 and 2003. In 2002 and 2003, >40% of breads made of enriched flour contained <115 microg of folate/100 g and >70% contained <160 microg/100 g. These percentages were markedly higher than those in 2001. Our data suggest that folic acid in breads containing enriched flour declined after 2001 and monitoring of fortification may be necessary.  相似文献   

Soil organic matter, effects on soils and crops   总被引：4，自引：0，他引：4  

A.E. Johnston 《Soil Use and Management》1986,2(3):97-105

Abstract. Manurial treatments and cropping history have remained unchanged for many years in classical and long-term experiments at Rothamsted and Woburn, in some cases for more than 100 years. Soil samples taken periodically have been analysed to follow changes in organic carbon content with time and treatment. Data presented here clearly show effects of carbon input and soil texture on equilibrium organic matter content.
Until recently increasing amounts of soil organic matter had little effect on yields of arable crops especially if fertilizer nitrogen dressings were chosen correctly. However the yield potential of many crops has increased and various agronomic inputs have become available to achieve that potential. Yields of many crops are now larger on soils with extra organic matter both on the sandy loam at Woburn and the silty clay loam at Rothamsted. Some of the effect appears to be related to extra water holding capacity, some to availability of nitrogen in ways which cannot be mimicked by dressings of fertilizer N, and some to improved soil physical properties. Responses to fertilizer N have been larger on soils with more organic matter.  相似文献   

母猪分娩的管理     

Lee J.Johnston  吴昊杰 《国外畜牧学(猪与禽)》2002,(4):31-33

从临产到仔猪断奶 ,是养猪业中最为劳动密集的生产阶段之一。本文根据最近在美国全国猪肉生产者协会支持下制订的分娩管理培训课程 ,提出一些要点以求刷新和精练我们的有关技术  相似文献   

Clinical and pathologic features of prostatic adenocarcinoma in sexually intact and castrated dogs: 31 cases (1970-1987).     

F W Bell  J S Klausner  D W Hayden  D A Feeney  S D Johnston 《Journal of the American Veterinary Medical Association》1991,199(11):1623-1630

The medical records of 31 dogs diagnosed with prostatic carcinoma at the teaching hospital between January 1970 and October 1987 were reviewed to determine whether gender status had an effect on the clinical features or biologic behavior of the disease. The only significant difference between sexually intact and castrated dogs was increased prevalence of pulmonary metastasis in castrated dogs.  相似文献   

Progesterone receptors in feline mammary adenocarcinomas   总被引：1，自引：0，他引：1  

S D Johnston  D W Hayden  D T Kiang  B Handschin  K H Johnson 《American journal of veterinary research》1984,45(2):379-382

Estradiol and progesterone receptors were measured in tumor cytosols from 3 intact and 4 neutered female cats with spontaneously occurring mammary adenocarcinomas. Serum from 2 of the intact cats which had been in estrus 4 and 4 to 6 weeks before tumor excision contained progesterone concentrations of 16.2 and 2.2 ng/ml, respectively; serum progesterone in the other cats was less than 2 ng/ml. Estradiol receptors were not detected in any cytosols. Progesterone receptors were detected in all of the cytosols, in concentrations ranging from 4.0 to 11.7 (mean = 7.2) fmol/mg of protein. Scatchard plot analysis of tumor cytosol from an 8th cat with mammary adenocarcinoma revealed presence of high affinity progesterone binding with a dissociation constant (Kd) of 3.47 nM. Tumor receptor content could not be correlated with stage of the estrous cycle nor with whether the cat was intact or neutered.  相似文献   

Nematodes and fungal diseases in barley and wheat on Prince Edward Island     

J. Kimpinski  R. V. Anderson  H. W. Johnston  R. A. Martin 《Crop Protection》1989,8(6):412-416

A total of 31 genera and 28 species of plant and soil nematodes were identified from 30 commercial fields each of barley and wheat on Prince Edward Island. Root-lesion nematodes, primarily Pratylenchus penetrans, were the dominant plant parasites, and the only endoparasitic nematodes recovered from roots. Root-lesion nematodes were the dominant genus in soil, but stunt nematodes (Tylenchorhynchus spp., primarily T. dubius, and Merlinius spp.), and pin nematodes (Paratylenchus spp.) were also recovered frequently. Common root rot, barley net blotch, and wheat leaf blotch, incited by Cochliobolus sativus, Pyrenophora teres, and Leptosphaeria nodorum, respectively, were prevalent in barley and wheat. The nematicide aldicarb reduced the numbers of root-lesion nematodes in roots and soil in experimental plots during 1984–1987, except from soil in wheat and barley in 1984 and in barley in 1986. Aldicarb treatments also increased grain yields significantly by 10% and 19% in 1984 and 1987, respectively. Aldicarb treatments did not affect the incidence of common root rot, barley net blotch, or wheat leaf blotch disease. Correlation and regression analyses of data from experimental plots did not indicate any significant relationships between population levels of root-lesion nematodes in roots or soil and severity of root or foliar diseases in barley or wheat.  相似文献   

Patent ductus arteriosus in the dog: characteristics of occurrence and results of surgery in one hundred consecutive cases.     

G E Eyster  J T Eyster  G B Cords  J Johnston 《Journal of the American Veterinary Medical Association》1976,168(5):435-438

The results of surgical repair of patent ductus arteriosus (100 dogs) were compared with the results of nonsurgical treatment of this defect (14 dogs). The death rate for dogs surgically treated was 8%, with 2 deaths at surgery and 6 late postoperative deaths. In the nonsurgical group, 64% died within one year of the examination. The increased survival rate for the surgically treated group was significant ( P less than 0.001). Surgical death rate was high for dogs more than 2 years old and weighing more than 23 kg. It was concluded that surgery is the preferred method of treatment and that early surgery increases the survival rate of dogs with patent ductus arteriosus, compared with the survival rate for older, heavier dogs with the defect.  相似文献   

Canine prostatic disease--comparison of radiographic appearance with morphologic and microbiologic findings: 30 cases (1981-1985)     

D A Feeney  G R Johnston  J S Klausner  V Perman  J R Leininger  M J Tomlinson 《Journal of the American Veterinary Medical Association》1987,190(8):1018-1026

A retrospective analysis was made of radiographs from 24 clinically normal young adult male Beagles used in previously reported base-line research on the distal male urinary tract. The ventrodorsal and craniocaudal prostate gland dimensions were measured, as visualized on the lateral radiographic view, and expressed as a ratio of the distance between the cranial aspect of the public bone and the sacral promontory. In 17 of these 24 dogs, there was sufficient image clarity to permit confident measurement of prostatic dimensions. From these data, the largest acceptable prostatic dimension, as visualized on the lateral radiographic view, was 70% of the public-promontory distance. A retrospective analysis was made of 30 cases of canine prostatic disease, with the objective of identifying the radiographic (survey and distention retrograde urethrocystogram) appearance most often associated with the various spontaneous prostatic diseases. Prostatomegaly was not specific for the cause of prostatic disease, except if the apparent parenchymal dimensions were greater than or equal to 90% of the public-promontory distance wherein neoplasia, abscess, and paraprostatic cysts (readily differentiated from diffuse intraparenchymal disease by ultrasonography) were the principle considerations. Multifocal, irregularly shaped, parenchymal mineral densities were observed only in dogs with prostatic carcinoma (4/7 cases) or prostatitis (1 case of chronic prostatitis). Narrowing of the prostatic portion of the urethra was observed only in association with abscess, neoplasm, or noninflammatory nonneoplastic disease (possibly benign hypertrophy/hyperplasia), whereas widening of this part of the urethra was not observed.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献