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41.
Water and nutrients were supplied to an Eucalyptus globulus plantation in a controlled experiment in west central Portugal. The trees were planted in a sandy soil at a spacing of 3 × 3 m. The experiment consisted of four treatments: irrigation, irrigation plus fertilization, fertilization without irrigation, and a rain fed and unfertilized control. The quantification of root biomass was carried out 13 mo after planting.When the plantation was 31 mo old, a trench was dug in the soil to uncover the distribution of the roots of individual trees. In the irrigated treatments root biomass was higher than in the control and in the fertilized plots. Differences in fine and coarse root distribution along the soil profile were also observed. In both irrigated treatments roots were concentrated along tree rows, where the irrigation tubes were dripping water or water plus nutrients. 相似文献
42.
Guillaume Laberge Per Ambus Henrik Hauggaard-Nielsen Erik Steen Jensen 《Soil biology & biochemistry》2006,38(7):1998-2000
The decline of N from 15N-labelled mature pea residues was followed in unplanted soil over 16.5 yr. Eight years after residue incorporation, 24% of the residue 15N input was still present in the soil and, after 16.5 yr, 16% of the residue 15N input remained. A double exponential model successfully described the decay of N from 15N-labelled pea residues. The total residual 15N declined with average decay constants of 1.45 yr−1 for the 30 d to 1 yr period and of 0.07 yr−1 for the 1-16 yr period. Sixteen years following incorporation of the residues, indicator plants growing in residues-amended soils were obtaining 1.7% of their N from residue N. This is, to our knowledge, the longest study on decay of N in soils from 15N-labelled crop residues. The current study thus provides a unique data set for our empirical understanding of N-dynamics in agricultural systems, which is a prerequisite to parameterize and validate N-simulation models. 相似文献
43.
Inter-observer agreement for assessment of faecal consistency in pigs was evaluated using a scoring system with 3 categories. In a pilot study, 3 observers performed an examination of faecal samples post-collection. The samples were obtained from pigs (12-13 weeks old) in 4 herds with a history of diarrhoea associated with Lawsonia intracellularis, Brachyspira spp. and/or Porcine Circovirus Type 2. Observer 1 examined all the faecal samples from the 4 herds. Observer 2 only examined the faecal samples from herds 1 and 2. Observer 3 only examined the faecal samples from herds 3 and 4. We observed a substantial agreement in faecal consistency scores between Observers 1 and 3 (kappa=0.64, 95% CI: 0.51-0.78). In contrast, only a fair agreement was observed between Observers 1 and 2 (kappa=0.24, 95% CI: 0.14-0.34). The variations in inter-observer agreement detected in the current study suggest that misclassification error can be a problem in studies assessing faecal consistency. Solutions may include developing a standardized system for scoring the consistency of pig faeces, calibration when more than one observer is involved in clinical studies and using a more objective measure of faecal consistency. 相似文献
44.
Steen Bech-Nielsen Goran Hugoson Maria Wold-Troell 《Preventive veterinary medicine》1983,1(4):303-320
An attempt to predict the rate of spread of and economic losses due to Parafiliaria bovicola infections in Swedish cattle was made for a 20-year period using the best epidemiological data available. By 1990, yearly losses in the absence of a control program may amount to 40 million Swedish crowns (8 million U.S.$). The estimated losses were compared to four presumptive eradication measures: (i) pharmaceutical treatment of cows with cutaneous Parafilaria bleeding, (ii) culling of bleeding cows, (iii) indoor management of bleeding cows, and (iv) pharmaceutical treatment of young livestock going to slaughter. Only the first three control programs will theoretically result in eradication of the parasite. The calculated benefit—cost ratios were 30.0, 5.9, 5.9 and 1.9 for (i), (ii), (iii) and (iv), respectively. 相似文献
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Summary The frequency of PMTV-spraing and TRV-spraing increased during storage in several cultivars. The only exception was cv. Saturna,
where a decrease was observed in 1992. A spraing inducing treatment of one week at 18 °C followed by one week at 8 °C immediately
after an early harvest increased the frequency and provided a rough estimate of the development of spraing in untreated tubers
during storage. Under most circumstances wound healing at 25 °C compared with 15 °C resulted in a lower frequency of spraing
during the storage period. The date of harvest had an important influence on development of spraing during storage and on
the effect of post harvest temperature treatments. Therefore, physiological processes that induce or erase spraing are strongly
related to tuber maturity. The mechanisms controlling development of symptoms seemingly are identical for the two spraing
inducing vira. 相似文献
49.
Summary Seventeen weed species common in the potato fields in Denmark were grown in a hydroponic system infested with viruliferous
zoospores ofSpongospora subterranea f.sp.subterranea carrying potato mop-top virus (PMTV). The plants were examined for infection with PMTV andS.s.s. using DAS-ELISA and based on visible symptoms. Only two weed species were found to be infected with PMTV,Chenopodium album andSolanum nigrum, whereas 13 became infected withS.s.s. C. album was infected with PMTV by mechanical inoculation were the infection became systemically and the leaves showed necrotic spots.S. nigrum became local infected with PMTV by mechanical inoculation. By inoculation with viruliferousS.s.s. the roots ofS. nigrum became infected but in three weeks PMTV had not spread into the top of the plants.Nicotiana benthamiana was used as a control susceptible toS.s.s. and PMTV. 相似文献
50.
Lars M. Hansen Steen L. Nielsen 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(2):132-137
Abstract Aphids are major vectors of plant viruses. Potato virus Y (PVY) is the most important aphid-transmitted virus affecting potato crops in Denmark. Because of a changed seed potato growing strategy, the seed potato area in Denmark is changing from regions with a low average temperature to regions with a higher average temperature. This means that the aphids may infest the potato crops earlier and the population development of the aphids may be faster, and consequently PVY may more easily become epidemic in seed potato crops. With a view to reducing the spread of PVY a 3-year experiment was carried out with a combination of mineral oil and insecticides. In 2005 and 2007 when a very high number of aphids were present, nearly all plants were infected with PVY. In 2006 with a lower number of aphids a smaller proportion of the plants were infected, and a tendency to a lower PVY incidence in mineral-oil treated plots was found, but more than the 8% threshold value. Even in plots where systemic neonicotinoids were applied and very few aphids were recorded, no significant reduction in infestation level of PVY was found. The present experiment shows that mineral oil and insecticides applied to potato crops each week for a 6-week period as protection against aphid transmission of PVY did not significantly reduce the level of PVY infestations in potatoes. 相似文献