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61.
62.
L. Blake K. W. T. Goulding C. J. B. Mott P. R. Poulton 《European Journal of Soil Science》2000,51(2):345-353
The usefulness of stored soils from long‐term experiments is often questioned because of changes that might occur during storage. We examined changes during long‐term storage (8–69 years) in the chemical properties of soils with a range of pH values (3.4–8.1 in water) from woodland and grassland experiments at Rothamsted Experimental Station in the UK. No significant changes during storage were measured for total C and N. Large but erratic changes in exchangeable Na+ content between 1959 and 1991 were probably caused by contamination of the 1959 samples by perspiration and from sodium‐based glassware. Exchangeable K+ increased during storage but only by a small amount. Small changes in exchangeable Ca2+ and Mg2+ were measured in some samples but not in others. Generally the amount of exchangeable cations increased slightly during storage. This is probably linked to the decreases of 0.4 units in the pH of acid soils, which we attribute to the hydrolysis of approximately 0.25% of the exchangeable Al3+. A doubling of the amount of exchangeable Mn2+ during storage for 32 years was probably caused by re‐equilibration of Mn species. The most practicable way to prepare soil samples for long‐term storage is to dry them in air. However, those who study changes in soil by re‐analysing samples of the soil stored for a long time must (i) use the same methods of analysis, or (ii) demonstrate that different methods lead to the same results, and (iii) know what changes can arise during storage. 相似文献
63.
Soluble organic nitrogen in agricultural soils 总被引:36,自引:0,他引:36
D. V. Murphy A. J. Macdonald E. A. Stockdale K. W. T. Goulding S. Fortune J. L. Gaunt P. R. Poulton J. A. Wakefield C. P. Webster W. S. Wilmer 《Biology and Fertility of Soils》2000,30(5-6):374-387
The existence of soluble organic forms of N in rain and drainage waters has been known for many years, but these have not
been generally regarded as significant pools of N in agricultural soils. We review the size and function of both soluble organic
N extracted from soils (SON) and dissolved organic N present in soil solution and drainage waters (DON) in arable agricultural
soils. SON is of the same order of magnitude as mineral N and of equal size in many cases; 20–30 kg SON-N ha–1 is present in a wide range of arable agricultural soils from England. Its dynamics are affected by mineralisation, immobilisation,
leaching and plant uptake in the same way as those of mineral N, but its pool size is more constant than that of mineral N.
DON can be sampled from soil solution using suction cups and collected in drainage waters. Significant amounts of DON are
leached, but this comprises only about one-tenth of the SON extracted from the same soil. Leached DON may take with it nutrients,
chelated or complexed metals and pesticides. SON/DON is clearly an important pool in N transformations and plant uptake, but
there are still many gaps in our understanding.
Received: 10 June 1999 相似文献
64.
SUMMARY The clinical, pathological and biochemical manifestations of maple syrup urine disease (MSUD) are similar in Poll Hereford and Poll Shorthorn X Poll Hereford calves. No significant differences were observed in branched-chain amino acid concentrations in plasma, or of branched-chain keto acid dehydrogenase activity in fibroblasts, between Poll Herefords homozygous normal and heterozygous for the mutation responsible for MSUD. Haemopoietic chimerism resulted in incorrect diagnosis of the MSUD genotype in 30% of non-identical twins when blood DNA was analysed using allele-specific amplification. Hair roots are shown to be a suitable source of target DNA for genotyping Poll Hereford cattle for the MSUD mutation. Twelve of 203 (5.8%) aged Poll Hereford bulls, sampled at saleyards during the last 4 months of 1993, were found to be heterozygous for the mutation. In contrast, the mutant sequence was detected in only 1 of 150 (0.7%) 2- and 3-year-old Poll Hereford bulls offered for sale at 2 stud sales held during 1993, suggesting that the prevalence of the disease may decline over the next few years. 相似文献
65.
66.
Since October 1982 three cases of cowpox infection of the cat have been presented at a veterinary practice. The disease began as a focal dermatitis on the face or paws which spread after several days to the rest of the body. Two weeks after appearing the pocks scabbed over and fell off leaving hairless skin. There were few systemic signs and therapy did not appear to influence the course of the disease. Diagnosis was confirmed by the demonstration of pox virions or inclusion bodies in skin biopsy or scab material using electron microscopy and by isolation of cowpox virus in chick embryos. High antibody titres to cowpox were observed in the sera of two cats. 相似文献
67.
68.
The comparative pathogenicity of four serovars of Actinobacillus (Haemophilus) pleuropneumoniae 总被引:1,自引:0,他引:1
The pathogenicity of 2 isolates of each of serovars 7, 3, 1 and 2 of Actinobacillus pleuropneumoniae was tested by intranasal inoculation into 60, 6-week-old large white pigs. Four dose rates varying from 0.27 to 560 x 10(6) organisms per pig with 10-fold serial dilutions were used. Surviving pigs were necropsied 7 days after inoculation. The proportion of pigs dying and developing gross lesions following infection was significantly greater for pigs given serotype 1 than for each of the other 3 serotypes, which did not differ significantly from each other. Twelve of 16 pigs given either of the 2 isolates of serovar 1 died after acute illness and 1 of 44 pigs given either of the 2 isolates each of serovars 7, 3 and 2 died. Pigs given serovar 1 showed high temperatures, severe respiratory distress, frothy haemorrhagic nasal discharge and weight loss. Lung lesions were produced in all 16 pigs given serovar 1, in 7 of 14 pigs given serovar 7, 7 of 14 pigs receiving serovar 3 and in 5 of 16 pigs given serovar 2. The lethal infections were characterised by a severe acute fibrinohaemorrhagic necrotising pleuropneumonia, whereas non-lethal cases had lung lesions ranging from necrotising purulent pleuropneumonia to abscessation. Significant differences between isolates in proportions of tissues culture positive for A. pleuropneumoniae for serovars 7 and 2, but not for serovars 3 and 1 suggested that isolates may vary in virulence within serovars, but more detailed studies are needed to clarify this point. 相似文献
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70.