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991.
Ng A Parker ML Parr AJ Saunders PK Smith AC Waldron KW 《Journal of agricultural and food chemistry》2000,48(11):5612-5617
The structure and mechanical properties of onions are important factors affecting their textural quality. The onion bulb consists of several layers of pigmented, papery scales surrounding fleshy storage scales that comprise an upper epidermis, an intermediate parenchyma tissue, and a lower epidermis. The purpose of this study was to examine the chemical composition of cell walls from the papery scales and outer fleshy scales of onion (Allium cepa L. cv. Sturon) in relation to their mechanical properties. Cell-wall material (CWM) was prepared from the component tissues and analyzed for its carbohydrate and phenolic composition. The CWMs were rich in uronic acid and glucose, with smaller quantities of arabinose, galactose, and xylose. In the fleshy scales, the lower epidermis contained relatively more galactose-rich pectic polysaccharides, whereas the upper epidermis and the papery scales contained virtually no galactose. Analysis of mechanical properties showed that the order of strength of the tissues was papery scales > fleshy scales, which were in the order lower epidermis > upper epidermis > intermediate parenchyma. The upper epidermis of fleshy scales was stronger in the vertical than the horizontal direction, and both orientations showed negligible notch sensitivity. Cyclohexane-trans-1,2-diaminetetraacetate-induced vortex-induced cell separation of the intermediate layer of fleshy scales indicated that calcium cross-linking may play an important role in cell-cell adhesion. A small but significant amount of ferulic acid was found in the walls, predominantly in the thick cuticle of the lower epidermis of fleshy scales. Alkali-labile wall-bound flavonoids were also detected. 相似文献
992.
Ten different topsoils representing members of three soil chronosequences were pre-treated with 0.1 M HC1 and extracted with neutral 0.1 M Na4P2O7 followed by 0.5 M NaOH. Extracts were purified and fractionated into five different nominal molecular weight fractions using gel filtration. With increasing soil development, the proportion of large molecules (>200 000) in the organic matter decreased with an increase in the proportion of intermediate size molecules (200 000 – 10 000). This effect was more evident in the mild Na4P2O7 extracts than in the subsequent NaOH extracts, and in soils of the Manawatu chronosequence than in those of the other two chronosequences and are attributed to changes in the nature and humification of soil organic matter during soil development. 相似文献
993.
Changes in soil properties and yield response in relation to tillage and residue management treatments in an irrigated groundnut (Arachis hypogea L.)—wheat (Triticum aestivum, L.) rotation on a sandy soil (1972–1974) and on a sandy loam soil (1974–1976) were evaluated. Tillage treatments (T1 and T2) did not cause significant changes in soil properties. Incorporation of crop residues (5 t residue per ha per crop, T3) caused a substantial increase in organic C, available N, and NaHCO3 -extractable P contents in the top 15 cm of both soils. Residue management treatments (T3, T4 and T5) showed no significant effect on soil bulk density and exchangeable K. Crop yields under no-tillage (T1) and conventional tillage (control, T2) were comparable on sandy soil but on the sandy loam soil, no-tillage yielded significantly lower than conventional tillage. Compared with the control, incorporation of crop residues (T3) caused higher yields on sandy soil for groundnut and wheat by 34.1 and 47.4%, respectively, and on sandy loam by 17.1 and 7.2%, respectively. Mulching with crop residues conserved soil moisture and reduced maximum soil temperature (1.5–5.3°C in groundnut and 1.5–2.9°C in wheat) but other measured soil properties were not significantly affected. Significant yield increase due to residue mulching (T4) was observed in sandy soil but it was significantly less than when total crop residue was incorporated (T3). Increased wheat root-weight density in the top 15 cm soil with residue mulching was not reflected in grain yield. Compared with the incorporation of the total amount of crop residue (T3), incorporation of half the amount and application of the other half as mulch (T5) caused lower yields — on sandy soil for groundnut and wheat by 31.5 and 15.7%, respectively, and on sandy loam by 4.8 and 3.6%, respectively. 相似文献
994.
Up to 1978 51% of brown trout populations and 27% of perch populations in the four southernmost counties of Norway were lost. During 1983 the fish status of lakes in the two southernmost counties which in the period 1974 to 1978 still had fish were updated. During the period 1978 to 1983, 30% of the remaining brown trout populations and 12% of the perch populations were lost. By 1983 71% of brown trout populations and 43% of perch populations in this area have been lost. In October 1983, 623 (77%) of the lakes were sampled for analyses of water quality. The status and change in fish populations during the period from 1974–78 to 1983 were highly related to water quality status. 相似文献
995.
Critical drainage and nitrate leaching losses from manures applied to freely draining soils in Great Britain 总被引:1,自引:0,他引:1
Abstract. Pig slurry was applied by open-slot injection to experimental plots on a sandy loam site at ADAS Gleadthorpe, Nottinghamshire. Volume and distribution of over-winter drainage were adjusted through the use of rainfall exclusion covers or irrigation. The resultant slurry N leaching over the range of drainage values tested (up to 300 mm) could be satisfactorily described by curve-fitting, using a quadratic or exponential function. Initial simulations of slurry N leaching using the manure nitrogen decision support system manner (v. 3.0) compared poorly with the experimental data, predicting both earlier and greater amounts of nitrate leaching. However, the lack of fit could be explained by consideration of the likely ammonia emissions following slurry injection, the actual volumetric soil moisture capacity at the experimental site and the likely time delay for the nitrification of slurry N following application. Good agreement between modelled and observed data was achieved when these factors were taken into account. The manner model was used to simulate nitrate leaching beyond the range of drainage treatments tested in the experiments and the anticipated sigmoidal relationship between nitrate leaching and drainage was observed. The model was then used to study the effects of manure application timing and the likely impact on nitrate leaching, across the range of rainfall conditions found in Great Britain. Simulations for a range of manure types were undertaken, with manures applied at rates up to the limit of permitted N loading on freely draining sandy loams. Rainfall inputs for these simulations were based on long-term average climatic data. Results are presented for two contrasting manure types, cattle slurry and poultry manure, both of which are subject to controls in Nitrate Vulnerable Zones (NVZs) in Great Britain. 相似文献
996.
Ingrid K Thomsen Per SchjønningJørgen E Olesen Bent T Christensen 《Soil biology & biochemistry》2003,35(6):765-774
The turnover of native and applied C and N in undisturbed soil samples of different texture but similar mineralogical composition, origin and cropping history was evaluated at −10 kPa water potential. Cores of structurally intact soil with 108, 224 and 337 g clay kg−1 were horizontially sliced and 15N-labelled sheep faeces was placed between the two halves of the intact core. The cores together with unamended treatments were incubated in the dark at 20 °C and the evolution of CO2-C determined continuously for 177 d. Inorganic and microbial biomass N and 15N were determined periodically. Net nitrification was less in soil amended with faeces compared with unamended soil. When adjusted for the NO3-N present in soil before faeces was applied, net nitrification became negative indicating that NO3-N had been immobilized or denitrified. The soil most rich in clay nitrified least N and 15N. The amounts of N retained in the microbial biomass in unamended soils increased with clay content. A maximum of 13% of the faeces 15N was recovered in the microbial biomass in the amended soils. CO2-C evolution increased with clay content in amended and unamended soils. CO2-C evolution from the most sandy soil was reduced due to a low content of potentially mineralizable native soil C whereas the rate constant of C mineralization rate peaked in this soil. When the pool of potentially mineralizable native soil C was assumed proportional to volumetric water content, the three soils contained similar proportions of potentially mineralizable native soil C but the rate constant of C mineralization remained highest in the soil with least clay. Thus although a similar availability of water in the three soils was ensured by their identical matric potential, the actual volume of water seemed to determine the proportion of total C that was potentially mineralizable. The proportion of mineralizable C in the faeces was similar in the three soils (70% of total C), again with a higher rate constant of C mineralization in the soil with least clay. It is hypothesized that the pool of potentially mineralizable C and C rate constants fluctuate with the soil water content. 相似文献
997.
In the Lower Cell of the Heath Steele mine tailings arealocated 50 km north of the city of Miramichi, New Brunswick,Canada, tailings and lime treatment sludge were co-depositedand the effluent occasionally exceeded regulatory dischargelimits for total suspended solids (TSS), especially on verywindy days. A combined field and laboratory investigationwas undertaken during 1998-1999 to identify the cause of thehigh TSS. The methodology included field measurement of windvelocity and sampling of bed tailings, sludge,suspended sediment, and the water cover. The samples werethen subjected to various laboratory examinations using x-raydiffraction, scanning electron microscopy interfacedwith energy dispersion x-ray spectroscopy, critical shearstress measurements, and water chemistry analysis. Thesuspended sediment was found to be composed primarily ofcalcite and metal hydroxides derived from the bed sludge inthe cell. Only a very small amount of tailings (less than5%) was detected in the suspended sediment. The sludge,which covered the tailings in the shallow western section ofthe Lower Cell at depths less than 1 m, was a loose, low-densitymaterial with a low critical shear stress (approximately 0.058 Pa). In shallow water cover (less than 1 m), calculated bed shearstress mobilized by wind-induced waves and return currents exceeded the critical shear on a number of occasions, resultingin resuspension of the sludge and hence high TSS. Although occasional elevated zinc concentrations appeared to follow a similar pattern to high TSS, there was no evidence that thesuspended sludge sediments would release metals into the watercover, due to the high pH of the Lower Cell water cover. Since the tailings did not resuspend significantly, it was clear thatat water cover depth less than 1 m, sludge was eroded instead oftailings, and thus provided a barrier against tailings resuspension. As part of the final closure scheme for the HeathSteele tailings area, sludge and tailings were dredged and relocated from areas where the water cover was < 1 m to deeperwater cover areas to ensure that the effluent met required totalsuspended solids discharge criteria. 相似文献
998.
Shivashankara KS Isobe S Al-Haq MI Takenaka M Shiina T 《Journal of agricultural and food chemistry》2004,52(5):1281-1286
Greenhouse-grown tree ripe (TR) and mature green (MG) mangoes (cv. Irwin) were exposed to high electric field treatment before 20 and 30 days of storage at 5 degrees C. MG fruits were allowed to ripen at room temperature after low-temperature storage. Fruit physical quality attributes, ascorbic acid, carotene, quercetin, total phenols, and antioxidant capacity were estimated before and after the storage period. Antioxidant capacity of fruit juice was estimated using the ferric reducing antioxidant power (FRAP) assay. Fruit firmness decreased significantly during storage. Titratable acidity decreased 20 days after storage. Total soluble solids did not change during storage. Antioxidant capacity of fruits remained unchanged up to 20 days of storage period and decreased thereafter. Total phenol and carotenes increased during storage. Antioxidant capacity of fruits was significantly correlated only to ascorbic acids. Peel color and carotenes were higher in TR fruits, whereas titratable acidity and firmness were higher in MG fruits. There was no significant difference in other parameters between the stages of picking. Electric field pretreatment affected the respiration and antioxidant capacity of TR fruits and did not have any significant affect on other parameters. TR mangoes of cv. Irwin are more suitable for low-temperature storage and can be successfully stored for up to 20 days at 5 degrees C without any significant losses in functional properties and quality attributes. 相似文献
999.
There is conflicting evidence about toxic effects of heavy metals in soil on symbiotic nitrogen fixation. This study was set-up to assess the general occurrence of such effects. Soils with metal concentration gradients were sampled from six established field trials, where sewage sludge or metal salts have been applied, or from a transect in a sludge treated soil. Additional contaminated soils were sampled near metal smelters, in floodplains, in sludge amended arable land and in a metalliferous area. Symbiotic nitrogen fixation was measured with 15N isotope dilution in white clover (Trifolium repens L.) grown in potted soil that was not re-inoculated, and using ryegrass (Lolium perenne L.) as reference crop. The fraction nitrogen in clover derived from fixation (Ndff) varied from 0 to 88% depending on soil. Pronounced metal toxicity on Ndff was only confirmed in a sludge treated soil where nitrogen fixation was halved from the control value at soil total metal concentration of 737 mg Zn kg−1, 428 mg Cu kg−1 and 10 mg Cd kg−1. The Ndff was significantly reduced by increasing metal concentration in soils from two other sites where Ndff was low throughout and where these effects might be attributed to confounding factors. No significant effects of metals on Ndff were identified in all other gradients even up to elevated total metal concentration (e.g. 55 mg Cd kg−1). The variation of Ndff among all soils (n=48), is mainly explained by the number of rhizobia in the soil (log MPN, log (cells g−1 soil)), whereas correlations with total or soil solution metal concentrations were weak (R2<0.25). The is significantly affected by the presence or absence of the host plant at the sampling site. No effects of metals were identified at even at total Zn concentrations of about 2000 mg Zn kg−1, whereas metal toxicity could be identified at lower most probable number (MPN) values. This survey shows that the metal toxicity on symbiotic nitrogen fixation cannot be generalized and that survival of a healthy population of the microsymbiont is probably the critical factor. 相似文献
1000.
Previous laboratory research has shown that biofilters have the potential to reduce CH4 emissions from landfills by as much as 83%. However, to achieve this level of CH4 reduction biofilters must be properly designed. The present study was conducted to develop a method for properly designing biofilters based on landfill size and location. A quadratic equation was developed to describe the dependence of CH4 oxidation rate in a sandy loam textured soil as a function of soil temperature, soil moisture and ammonium nitrogen concentration. Using this equation and the average monthly soil temperature and moisture contents for the largest cities of each of the 48 contiguous states, the monthly CH4 oxidation rate at each location was calculated. Then, assuming a standard landfill depth of 27.6 m, and a standard area of 121,500 m2, the required biofilter size was calculated. Finally, the ratio of biofilter size to landfill size was calculated. Design calculations for biofilters located in the states of Alabama, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina and Texas where the CH4 oxidation rates are relatively high throughout the year indicate that the necessary biofilter sizes are small. In addition, biofilters in these states may be expected to be effective throughout the year. In contrast, the calculations indicated biofilter systems in the states of Idaho, Minnesota and North Dakota will have much lower efficiencies during much of the year due to unfavorable soil moisture and temperature ranges. Given proper design, installation and management, a biofilter should be capable of achieving a significant reduction in atmospheric CH4 emission as compared to emissions from the same landfill without a biofilter. 相似文献