PHOSPHORUS TRANSFORMATIONS IN A CHRONOSEQUENCE OF SOILS DEVELOPED ON WIND-BLOWN SAND IN NEW ZEALAND     

J. K. SYERS  T. W. WALKER 《European Journal of Soil Science》1969,20(2):318-324

The rate of transformation of inorganic phosphorus fractions and forms was investigated in a chronosequence of weakly weathered soils developed on windblown sand. The net decline of acid-extractable Ca-P during 10⁴ years of soil development was approximately 2600 kg/ha m profile. This fraction was progressively removed from surface horizons and had virtually disappeared from the oldest soil. Residual inorganic P, considered to be included apatite which is not extracted by 0·5 and 1N HC1, was relatively constant in profiles of the chronosequence but decreased in the oldest soil. In the younger soils, the NH₄F-P fraction was low but, with increasing time, the weight of this fraction increased, initially in surface horizons. The net accumulation of non-occluded secondary inorganic P during 10⁴ years was 360 kg/ha m profile and this was largely due to an increase in the NH₄F-P, rather than the 1st NaOH-P fraction. There was no net shift from non-occluded to occluded secondary inorganic P. Although apatite is initially present as inclusions within primary minerals in the wind-blown sand, an extensive loss of P has occurred during 10⁴ years.  相似文献   

Crystallinity of soil kaolinites in relation to clay particle-size and soil age     

D. J. CHITTLEBOROUGH  P. H. WALKER 《European Journal of Soil Science》1988,39(1):81-86

The crystallinity of soil kaolinites as a function of clay particle-size and soil age was investigated in soil chronosequences of the Shingle House Creek and Hawkesbury River alluvial terraces in south-eastern Australia. The youngest soils (late Holocene) in each sequence are texturally uniform Entisols containing kaolinite and illite. The oldest soils (Pleistocene to late Tertiary) are Ustalfs with strong textural differentiation and are predominantly kaolinitic. With increasing age, textural B horizons are increasingly enriched in kaolinite and in particles of fine clay (< 0.2 μm) size. In two sub-fractions of the fine clay (0.2-0.06 μm; < 0.03 μm), no corresponding changes were observed in the crystallinity of kaolinites (as measured by the index, C _k) with age. However, values of C _k were significantly higher in the coarse clay (2-0.2 μm) than for both fine clay fractions in all except the Ultic Paleustalf of the oldest, possibly late Tertiary, terrace of the Hawkesbury River sequence. In this soil, C _k values are low in all three clay-size fractions.
In these sequences, the effects of both clay particle-size and soil age were identified in the crystallinity of kaolinites. Disorder as a result of pedogenesis, however, was associated only with the most prolonged weathering and the strongest soil textural differentiation.  相似文献   

Mycotic dermatitis in a freshwater gizzard shad, the bony bream, Nematalosa erebi (Günther), in the River Murray, South Australia     

J. T. PUCKRIDGE  K. F. WALKER  J. S. LANGDON  C. DALEY  G. W. BEAKES 《Journal of fish diseases》1989,12(3):205-221

Abstract. The lower Murray population of bony bream is subject to an annual epidemic of the oomycete Saprolegnia (principally S. parasitica ) and the bacterium Aeromonas hydrophila. The epidemic is species-specific; it mainly affects adults whose susceptibility may be increased by stress due to winter cold. Lesions occur on the mid-flank and are characterized by an external mycelium, epidermal erosion, scale loss, hypodermal and muscular oedema, haemorrhage, myofibril degeneration and by the presence of Saprolegnia hyphae at all stages of infection. Although A. hydrophila is common in advanced lesions there is no significant systemic bacterial infection. This appears to be a primary mycotic dermatitis and is noteworthy because Saprolegnia is best-known as a secondary pathogen.  相似文献   

An assessment of the efficacy of two lysine microencapsulation techniques to determine the quantitative lysine requirement of the South African abalone, Haliotis midae L.   总被引：2，自引：0，他引：2  

T.A. SHIPTON  P.J. BRITZ  & R.B. WALKER 《Aquaculture Nutrition》2002,8(3):221-227

The quantification of the essential amino acid requirements of a species is a prerequisite to the formulation of biologically optimized diets. In this study, crystalline L -lysine was used in an attempt to determine the quantitative lysine requirement of juvenile Haliotis midae . Two microencapsulation techniques [gelatine/acacia and cellulose acetate phthalate (CAP)] were used to retard leaching of crystalline L -lysine incorporated into semipurified test diets. An assessment of the efficacy of the encapsulation techniques, revealed that despite effective lysine supplementation, H. midae fed semipurified test diets containing encapsulated crystalline L -lysine failed to promote significant improvements in either growth, feed or protein efficiency ( P  > 0.05). The failure of the crystalline L -lysine to illicit growth and nutritional responses is discussed.  相似文献   

Anorexia and progressive weight loss in long-term feeding experiments with sheep     

K. H. WALKER  J. M. THOMPSON  R. F. BAYFIELD  D. PERRY 《Australian veterinary journal》1984,61(6):193-194

  相似文献   

Aspects of the selective phytotoxicity of methazole. I. Measurements of species response, spray retention and leaf surface characteristics   总被引：1，自引：0，他引：1  

JULIE VERITY  ALLAN WALKER  DONALD S. H. DRENNAN† 《Weed Research》1981,21(5):243-253

The responses of onion (Allium cepa). Veronica persica, Matricaria matricarioides and Stellaria media to post-emergence applications of methazole were measured in field and glasshouse experiments. Stellaria media was the most susceptible species and V. persica the least. Plants of all species became more tolerant the larger they were at the time of treatment, and this was most pronounced in onion. Onion generally retained less spray per unit of dry weight than the other three species and retention was less on old compared with young plants, whereas with the weed species, this did not change appreciably with age. There was a progressive increase in the amount of structured crystalline wax on successive onion leaves which resulted in larger contact angles between droplets and the leaf surfaces and lower spray retention per unit of dry weight. There was less wax development on the leaf surfaces, increased spray retention, and increased susceptibility to methazole in onion treated pre-emergence with ethofumesate thus confirming that these factors are interrelated. While the increased tolerance of onion to methazole with age could be explained in part by decreased retention of herbicide, this was not so for the weed species, and other factors must determine their change in tolerance with age.  相似文献   

Spatial variability in the degradation rates of isoproturon and chlorotoluron in a clay soil     

A WALKER  R H BROMILOW  P H NICHOLLS  A A EVANS  V J R SMITH 《Weed Research》2002,42(1):39-44

Thirty separate soil samples were taken from different locations at the Brimstone farm experimental site, Oxfordshire, UK. Incubations of isoproturon under standard conditions (15 °C; ?33 kPa soil water potential) indicated considerable variation in degradation rate in the soil, with the time to 50% loss (DT₅₀) varying from 6 to 30 days. These differences were confirmed in a second comparative experiment in which degradation rates were assessed in 11 samples of the same soil in two separate laboratories using an identical protocol. There was a significant negative linear relationship (r²= 0.746) between the DT₅₀ values and soil pH in this group of soils. In a third experiment, degradation rates of the related compound chlorotoluron were compared with those of isoproturon in 12 separate soil samples, six of which had been stored for several months, and six of which were freshly collected from the field. Degradation of both herbicides occurred more slowly in the stored samples than in the fresh samples but, in all of them, chlorotoluron degraded more slowly than isoproturon, and there was a highly significant linear relationship (r²=0.916) between the respective DT₅₀ values.  相似文献   

A COMPARISON OF REAL-TIME ULTRASOUND, PALPATION AND RADIOGRAPHY IN PREGNANCY DETECTION AND LITTER SIZE DETERMINATION IN THE BITCH     

ROBERT L. TOAL  DVM  MS    MICHAEL A. WALKER  DVM    GEORGE A. HENRY  DVM 《Veterinary radiology & ultrasound》1986,27(4):102-108

Fifty-five bitches were examined once, at different intervals for pregnancy. Manual Papation, B-mode real-time ultrasoungraphy, and radiography were used to confirm pregnancy and to count the number of fetuses present. Predicted numbers were compared to whelping data obtained from owners. Radiography was confined to the last trimester of pregnancy and had an overall accuracy of 100% in pregnancy detection and 93% in correct litter size determination. A proor qualtiy radiograph contributed to the one incorrect count estimate. Ultrasound and palpation were used in all three trimester phases starting 3 weeks post coitus. For pregnancy detection ultrasound was 94% accurate (no false positives) and palpation was 88% accurate (one false positive). For fetal counting, ultrasound was 36% accurate and palpation was 12% accurate. Recommendations for the use of ultrasound and radiography in pregnancy evaluation are reviewed.  相似文献   

Bilateral Calcaneal Epiphysiolysis in a Dog     

RENE T. VAN EE dvm  TOMMY L WALKER dvm  ms  Dipiomateacvs  C. S. PATTON dvm  ms JAMIE R. BELLAH dvm 《Veterinary surgery : VS》1986,15(1):60-64

Ununited epiphyses were seen in the calcanei of a 13-month-old Rottweiler with abnormal rear limb conformation. Histologic examination of the tissues showed a nonunion with neoarthrosis formation. Surgical management included use of tension band and lag screw techniques to achieve epiphysiodesis that was radiographically evident 12 weeks postsurgery. There was no sign of lameness when examined 8 months after surgery. Similarities exist between this case and that of osteochondrosis in other domestic species, and with Osgood-Schlatters disease in humans. Osteochondrosis and/or abnormal angulation of the hocks were suspected as the underlying cause of the epiphyseal separations.  相似文献   

Germination, persistence, and emergence of flaxleaf fleabane (Conyza bonariensis [L.] Cronquist)     

HANWEN WU  STEVE WALKER  MICHAEL JONATHAN ROLLIN  DANIEL KEAN YUEN TAN  GEOFF ROBINSON  JEFF WERTH 《Weed Biology and Management》2007,7(3):192-199

Flaxleaf fleabane ( Conyza bonariensis [L.] Cronquist) is a difficult-to-control weed in dryland minimum tillage farming systems in the northern grains region of Australia. Experiments under field and controlled environments were conducted to study the seed germination, emergence, and persistence of C. bonariensis . The base, optimum, and maximum temperatures for seedling germination were estimated at 4.2, 20, and 35°C, respectively, with light stimulating germination. The soil types and burial depths had significant effects on seed persistence and emergence. The persistence pattern showed an initial rapid drop, followed by a slow but steady decline over time. After 3 years of burial, there were ≈ 7.5%, 9.7%, and 1.3% viable seeds at 10, 5, and 0–2 cm soil depths, respectively. Conyza bonariensis predominantly emerged from the soil surface or from the burial depth of 0.5 cm. Very few seeds emerged from a depth of 1 cm and none emerged from ≥ 2 cm. The emergence was greater in lighter soils. On-farm monitoring of the field emergence over time in a light sandy loam soil showed that 99% emergence occurred in late autumn, early and late winter, and a small fraction of 1% emerged in mid-spring. The predominant emergence from the soil surface suggests that the fleabane problem is a result of weed species shift toward the minimum tillage systems that provide moist conditions for better emergence compared to conventional tillage systems. The seed longevity of at least 3 years in the soil and the prolonged emergence patterns between autumn and spring have posed great difficulties for the long-term management of C. bonariensis .  相似文献