Root characteristics of selected field crops: data from the Wageningen Rhizolab (1990-2002)

Since being built in 1990, the rhizotron facility in Wageningen, the Wageningen Rhizolab, has been used for experiments on crops (e.g. Alfalfa, Brussels sprouts, common velvet grass, field bean, fodder radish, leeks, lupins, maize, potato, beetroot, ryegrass, spinach, spring wheat, winter rye and winter wheat). In the experiments, horizontal glass minirhizotron tubes combined with auger sampling were used to assess rooting characteristics. For this paper we took the root data from these experiments and looked for a general relationship between thermal time/time after planting and rooting depth, the velocity of the root front and root proliferation. For certain depths (fixed by the depth at which the horizontal minirhizotrons were installed) a simple linear regression was established between the average root number per cm2 minirhizotron surface area and thermal time after planting. The compartments selected for each crop were those in which there had been a control treatment and/or in which conditions for rooting were considered to be optimal. We performed regression analyses per compartment and per depth, but only for the period after planting in which a linear increase of root numbers vs. thermal time was observed. After averaging the results, the regression procedure yielded two parameters of rooting for each crop: (a) the actual or thermal time at which the first root appeared at a certain depth and (b) the root proliferation rate after the first root had appeared. In this way, inherent crop differences in rooting behaviour (rooting depth and root proliferation) became apparent. For each crop, the velocity of the root front after planting could be established (calculated in cm(°C day)-1). This parameter differed greatly between crops. Some crops (such as leeks and common velvet grass) explored the soil profile slowly: the root front moved at a velocity of only 0.07cm(°C day)-1. Among the crops whose roots grew down much faster (0.18-0.26cm (°C day)-1) were cereals and fodder radish. For a day with an average temperature of 15°C these rates would have corresponded with the root front travelling approximately 1-4cm per day. In the crops studied the root front velocity did not correlate with the root proliferation rat

Metingen en berekeningen van afbraak van organische stof in grond

In een rotatie met suikerbieten voor aardappelen werd geconstateerd dat er meer en langere blauwkleuring van de grond optrad, veroorzaakt door anaerobe afbraak van het ondergeploegde bieteblad en de bietekoppen, dan in de andere rotaties. Uit laboratoriumproeven werd geconcludeerd dat belemmeringen in de zuurstofaanvoer eerder oorzaak hiervoor zijn dan een bijzondere verteringskarakteristiek van de bietenresten. Uit verder onderzoek bleek nog dat de grootste omzettingssnelheden plaatsvonden vlak na het onderploegen en in mei en jun

De relatie tussen de samenstelling van koeie-urine en het optreden van urinebrandplekken in grasland

Het gehalte aan ureum, stikstof, hippuurzuur, kalium, natrium en de geleidbaarheid van elke urine-lozing van 10 melkkoeien werd gemeten, waarbij de bijbehorende schade aan de grasmat werd geregistreerd, om de relatie tussen urine-samenstelling en de mate van verbranding van de graszode nader te onderzoeken. De lozingen van 6.00-12.00 uur hadden gemiddeld het hoogste gehalte aan ureum en N-totaal en de lozingen van 18.00-24.00 uur het laagste. Hetzelfde geldt voor de geleidbaarheid. Het ureumgehalte in de urine bleek de mate van verbranding het beste te verklare

The Physical Principles of Quantum Mechanics. A critical review

The standard presentation of the principles of quantum mechanics is critically reviewed both from the experimental/operational point and with respect to the request of mathematical consistency and logical economy. A simpler and more physically motivated formulation is discussed. The existence of non commuting observables, which characterizes quantum mechanics with respect to classical mechanics, is related to operationally testable complementarity relations, rather than to uncertainty relations. The drawbacks of Dirac argument for canonical quantization are avoided by a more geometrical approach.Comment: Bibliography and section 2.1 slightly improve

Estimating incidence of venous thromboembolism in COVID-19:Methodological considerations

Background Coagulation abnormalities and coagulopathy are recognized as consequences of severe acute respiratory syndrome coronavirus 2 infection and the resulting coronavirus disease 2019 (COVID-19). Specifically, venous thromboembolism (VTE) has been reported as a frequent complication. By May 27, 2021, at least 93 original studies and 25 meta-analyses investigating VTE incidence in patients with COVID-19 had been published, showing large heterogeneity in reported VTE incidence ranging from 0% to 85%. This large variation complicates interpretation of individual study results as well as comparisons across studies, for example, to investigate changes in incidence over time, compare subgroups, and perform meta-analyses. Objectives This study sets out to provide an overview of sources of heterogeneity in VTE incidence studies in patients with COVID-19, illustrated using examples. Methods The original studies of three meta-analyses were screened and a list of sources of heterogeneity that may explain observed heterogeneity across studies was composed. Results The sources of heterogeneity in VTE incidence were classified as clinical sources and methodologic sources. Clinical sources of heterogeneity include differences between studies regarding patient characteristics that affect baseline VTE risk and protocols used for VTE testing. Methodologic sources of heterogeneity include differences in VTE inclusion types, data quality, and the methods used for data analysis. Conclusions To appreciate reported estimates of VTE incidence in patients with COVID-19 in relation to its etiology, prevention, and treatment, researchers should unambiguously report about possible clinical and methodological sources of heterogeneity in those estimates. This article provides suggestions for that.Thrombosis and Hemostasi