Environmental factors and cultural measures affecting the nitrate content in spinach

Ingestion of high amounts of nitrate by man can be considered hazardous to human health. In the human body, nitrate can be reduced to nitrite which may cause methemoglobinemia. Furthermore, the possible formation of N-nitroso-compounds from nitrite and secondary nitrogen compounds in the human stomach constitutes a risk, as for laboratory animals many N-nitroso-compounds have been shown to act as potent carcinogens.In the Netherlands, acceptable daily intakes of nitrate and nitrite, as set by the FAO/WHO for additives, are sometimes exceeded. The intakes of nitrate and nitrite therefore should be reduced. As nitrite intake is linked to nitrate intake which for about 75% is of vegetable origin, the nitrate contents of vegetables should be suppressed as much as possible.Spinach is one of the vegetables frequently having a high nitrate content. In the Netherlands, most spinach is grown for the processing industry and a portion of the processed spinach is used as baby food.Many environmental factors and cultural measures can affect the nitrate content in spinach. A review of relevant literature is presented in chapter 2. In the present study, some of these environmental factors have been investigated with respect to their influences on nitrate content and yield of spinach. Most attention, however, has been given to cultural measures, especially those concerning application of nitrogen fertilizers.The materials and methods used in this study are discussed in chapter 3 .In chapter 4, the results of experiments carried out indoors, with water-, sand- and soil-cultures, are described. In water-culture experiments, the cation:anion uptake ratio for spinach supplied with nitrate as sole nitrogen source, proved to be close to unity. When nitrogen (NO 3 ) was withheld from the spinach plants over a 3- or 9-day period, the nitrate contents in the aerial parts significantly decreased (section 4.2).In sand-culture experiments spinach showed very poor growth when supplied with ammonium-nitrogen only. With both ammonium- and nitratenitrogen added, the nitrate contents in spinach proved to be not always lower than with nitrate-nitrogen only. On a whole-plant basis, the carboxylate (C-A) : organic nitrogen ratio was found to reflect the extent of nitrate- or ammonium nutrition fairly closely (section 4.3).In soil-culture experiments both the nitrate contents and dry-matter yields of spinach were found to be strongly affected by the amount of nitrate applied. Yields usually showed a maximum, whereas nitrate contents did not. The nitrate contents in petioles of spinach were considerably higher than in laminae, and nitrate accumulated mainly in older leaves. In most soil-culture experiments, the nitrate contents in the aerial parts of spinach decreased with increasing age of the plants. Nitrate contents in autumn-grown spinach were higher than those in spinach grown in spring. Variations in timing of application of nitrate-nitrogen did not affect the nitrate contents. Compared with a normal soil- moisture content, a low soil-moisture content was found to increase, and a high sod- moisture content was found not to affect the nitrate content in spinach. Liming a sandy soil, resulting in increased soil pH-values, caused the nitrate contents in spinach to decline. Molybdenum applied as a spray onto the leaves of spinach, grown on a sandy as well as on a clayloam soil, did not have any effect on the nitrate contents in the aerial parts, but differences in soil type appeared to affect these contents (section 4.4).In a soil-culture experiment with a sandy soil, NH 4 -N dressings produced higher nitrate contents and lower dry-matter yields of spinach than did NO 3 -N-dressings. With the use of a nitrification inhibitor (DCD), however, lower nitrate contents were found with NH 4 -N-dressings. With a clay-loam soil used in a growth-chamber experiment, replacement of about 30% of the NO 3 -N by NH 4 -N with a nitrification inhibitor (nitrapyrin) added, did not result in a decrease in nitrate content, but replacement of about 60% of the NO 3 -N by NH 4 -N did. In the same experiment, a decrease in light intensity from 70 to 33 W per m 2and a rise in temperature from 12 to 22°C caused the nitrate content in spinach to increase (section 4.5).In a comparison of different N-carriers in a soil culture, positive results were obtained with sulphur-coated urea (section 4.6), with farmyard manure and pig- manure slurry (section 4.7), when plant-available N was taken into account. Variations in P-dressings as well as in soil P-status did not affect the nitrate content and yield of spinach (section 4.8). K-dressings in general increased the nitrate contents and yields of spinach, with K 2 SO 4 more than KCl being responsible for increases in nitrate contents (section 4.9).Large differences among spinach varieties were found with respect to nitrate contents in leaves (section 4. 10).In chapter 5, the results of experiments conducted outdoors are described. In the field experiments, yield, NO 3 - and N(total)-contents and total N in the aerial parts of spinach increased with increasing amounts of NO 3 -N applied. With the highest NO 3 -dressings, NO 3 -N accounted for 9-27% of the total N in spinach. The corresponding NO 3 -contents ranged from 300 to 1100 mmol per kg DM. In one experiment, varietal differences in N03 -content ' could be attributed to differences in age of the crop. Differences in NO 3 -contents between 'morning' and 'evening' harvests were found only on a bright day with high irradiation and with high NO 3 -levels in the plants.Available N in the sod profile before sowing ranged from 32 to 72 kg N per ha in the five spring experiments and from 40 to 132 kg N per ha in the two autumn experiments. In general, the net mineralization of organic N during the experimental periods was about 35 kg N per ha. Nitrogen appeared to be taken up by spinach mainly from the top 60 cm of the soil profile. Of the plant nutrients other than N only the contents of SO 4 and H 2 PO 4 were not affected by variations in NO 3 -dressing (section 5.1).Variations in timing of nitrogen applications affected yields in one, but not in another field experiment. NO3- and N(total)-contents and total N in the aerial parts of spinach in general decreased due to a partitioning of total N applied in one field experiment, whereas in another one, top-dressed N applied as NH 4 or NH 4 +NO 3 resulted in lower values than did comparable dressings of NO 3 (section 5.2).Due to partial or complete replacement of NO 3 -N by NH 4 -N, yields, NO 3 - and N(total)-contents, total N and the ratio (C-A):organic N in the aerial parts of spinach decreased in three field experiments, the effects in general being more pronounced with than without a nitrification inhibitor added. In two other field experiments, the effects of variations in NO 3 :NH 4 -ratio were much less pronounced or absent (section 5.3).On farmers' fields with 'low' N-dressings, plant-available N (= N-dressings plus the amount of available N in the soil before sowing) ranged from 135 to 175 kg N per ha, while with 'high' N-dressings plant-available N ranged from 200-415 kg N per ha. Compared with 'high' N-dressings, yields with 'low' N-dressings on the average were 17% lower, while NO 3 -contents were 64% lower (section 5.4).A discussion of the results is presented in chapter 6. Measures aimed at utilizing or manipulating environmental and soil conditions, at exploiting varietal differences and those aimed at regulating nutritional conditions, other than the ones governed by nitrogen, with the purpose of growing spinach with an economically acceptable yield level and with a low NO 3 -content, are dealt with in section 6.1.Experimentation aimed at finding the proper amount, the proper form and the proper timing of application of N for attaining the above-mentioned goal, is discussed in section 6.2. In the latter, special attention is paid to the relationship between the quantity of plant-available N (= N-dressing plus the amount of available N in the soil before sowing) and the NO 3 -content in spinach leaves. Based on data from spring field experiments and from experiments on farmers' fields, the amounts of plant- available N with which critical levels of NO 3 -contents are not surpassed, are presented. Recommendations for practical use in commercial spinach growing are formulated in the final portion of section 6.2

New limits on a cosmological constant from statistics of gravitational lensing

We present new limits on cosmological parameters from the statistics of gravitational lensing, based on the recently revised knowledge of the luminosity function and internal dynamics of E/S0 galaxies that are essential in lensing high-redshift QSOs. We find that the lens models using updated Schechter parameters for such galaxies, derived from the recent redshift surveys combined with morphological classification, are found to give smaller lensing probabilities than earlier calculated. Inconsistent adoption of these parameters from a mixture of various galaxy surveys gives rise to systematic biases in the results. We also show that less compact dwarf-type galaxies which largely dominate the faint part of the Schechter-form luminosity function contribute little to lensing probabilities, so that earlier lens models overestimate incidents of small separation lenses. Applications of the lens models to the existing lens surveys indicate that reproduction of both the lensing probability of optical sources and the image separations of optical and radio lenses is significantly improved in the revised lens models. The likelihood analyses allow us to conclude that a flat universe with Omega=0.3(+0.2-0.1) and Omega+Lambda=1 is most preferable, and a matter-dominated flat universe with Lambda=0 is ruled out at 98 % confidence level. These new limits are unaffected by inclusion of uncertainties in the lens properties.Comment: 30 pages, 9 ps figures, AASTeX, ApJ in pres

Expected constraints on the generalized Chaplygin equation of state from future supernova experiments and gravitational lensing statistics

This paper aims to study the use of future SNAP data together with the result of searches for strong gravitational lenses in future large quasar surveys to constrain the Generalized Chaplygin Gas (GCG) model. The GCG is considered as a possible unification scheme for dark matter-dark energy. It is found that both experiments should be able to place important constraints on the model, especially when both tests are used together.Comment: Submitted to the Astrophysical Journal, 33 pages, 8 Figures, uses aastex.cls. Changed for publication. Sections where the GCG is used as a dark energy candidate have been eliminated, plus minor change

Hora est! On dissertations

Catalogue of an exhibition in Leiden University Library, December 8, 2005-February 4, 2006ASC – Publicaties niet-programma gebonde

Determining the Hubble Constant from the Gravitational Lens PG 1115+080

For the quadruple gravitational lens PG 1115+080, we combine recent measurements of the time delays with new lens models to determine the Hubble constant H_0. We explore the effects of systematic uncertainties in the lens models on the estimates of H_0, and we discuss how the uncertainties can be reduced by future observations. We find that the lens cannot be fit by an isolated lens galaxy, but that it can be well fit by including a perturbation from the nearby group of galaxies. To understand the full range of systematic uncertainties it is crucial to use an ellipsoidal galaxy and to let the group position vary. In this case, the existing constraints cannot break degeneracies in the models with respect to the profiles of the galaxy and group and to the position of the group. Combining the known time delays with a range of lens models incorporating most of the plausible systematic effects yields H_0 = 51_{-13}^{+14} km s^{-1} Mpc^{-1}. The constraints on the lens models, and hence on H_0, can be improved by reducing the standard errors in the lens galaxy position from 50 mas to \sim10 mas, reducing the uncertainties in the time delays to \sim0.5 days, and constraining the lens mass distribution using HST photometry and the fundamental plane. In particular, the time delay ratio r_{ABC} = \Delta\tau_{AC} / \Delta\tau_{BA} may provide the best constraint on the mass profile of the galaxy.Comment: revised to use the updated time delays of Bar-Kana astro-ph/9701068; 30 pages, 7 Postscript figures, to appear in Ap

Shear and Ellipticity in Gravitational Lenses

Galaxies modeled as singular isothermal ellipsoids with an axis ratio distribution similar to the observed axis ratio distribution of E and S0 galaxies are statistically consistent with both the observed numbers of two-image and four-image lenses and the inferred ellipticities of individual lenses. However, no four-image lens is well fit by the model (typical $\chi^2/N_{dof} \sim 20$), the axis ratio of the model can be significantly different from that of the observed lens galaxy, and the major axes of the model and the galaxy may be slightly misaligned. We found that models with a second, independent, external shear axis could fit the data well (typical $\chi^2/N_{dof} \sim 1$), while adding the same number of extra parameters to the radial mass distribution does not produce such a dramatic improvement in the fit. An independent shear axis can be produced by misalignments between the luminous galaxy and its dark matter halo, or by external shear perturbations due to galaxies and clusters correlated with the primary lens or along the line of sight. We estimate that the external shear perturbations have no significant effect on the expected numbers of two-image and four-image lenses, but that they can be important perturbations in individual lens models. However, the amplitudes of the external shears required to produce the good fits are larger than our estimates for typical external shear perturbations (10-15% shear instead of 1-3% shear) suggesting that the origin of the extra angular structure must be intrinsic to the primary lens galaxy in most cases.Comment: 38 pages, 9 figures, submitted to Ap

Sagopilone (ZK-EPO, ZK 219477) for recurrent glioblastoma. A phase II multicenter trial by the European Organisation for Research and Treatment of Cancer (EORTC) Brain Tumor Group

Background: Sagopilone (ZK 219477), a lipophylic and synthetic analog of epothilone B, that crosses the blood-brain barrier has demonstrated preclinical activity in glioma models. Patients and methods: Patients with first recurrence/progression of glioblastoma were eligible for this early phase II and pharmacokinetic study exploring single-agent sagopilone (16 mg/m2 over 3 h every 21 days). Primary end point was a composite of either tumor response or being alive and progression free at 6 months. Overall survival, toxicity and safety and pharmacokinetics were secondary end points. Results: Thirty-eight (evaluable 37) patients were included. Treatment was well tolerated, and neuropathy occurred in 46% patients [mild (grade 1) : 32%]. No objective responses were seen. The progression-free survival (PFS) rate at 6 months was 6.7% [95% confidence interval (CI) 1.3-18.7], the median PFS was just over 6 weeks, and the median overall survival was 7.6 months (95% CI 5.3-12.3), with a 1-year survival rate of 31.6% (95% CI 17.7-46.4). Maximum plasma concentrations were reached at the end of the 3-h infusion, with rapid declines within 30 min after termination. Conclusions: No evidence of relevant clinical antitumor activity against recurrent glioblastoma could be detected. Sagopilone was well tolerated, and moderate-to-severe peripheral neuropathy was observed in despite prolonged administratio