In order to discern any relationship between added nitrate and microbial growth in a field plot, a Hanford sandy loam was infiltrated for 5 weeks at a rate of 5 cm day−1 with a solution containing 100 ppm ‐N and 1.25 meq/liter Cl− as KNO3 and CaCl2 respectively. Nitrate‐N, NO2−‐N and Cl− concentrations in soil solution were determined and corresponding counts of nitrate reducers, denitrifiers, and NH4+‐ and NO2−‐oxidizer populations were made.Ratios of measured to applied concentrations for both NO3−‐N and Cl− were nearly identical in all solution samples taken from the unsaturated soil profile, i.e., nitrate reduction was not pronounced and NO2−‐N was less than 1 ppm.Nitrate reducer populations (6x104–6x105/g soil) were always larger than those of denitrifiers (3x103–3x104/g) and varied little with time and depth. Ammonium oxidizers (101–105/g) generally decreased with depth. In contrast, NO2− oxidizers (101–3x106/g) varied markedly with time at all depths. An increase in numbers of NO2− oxidizers, after 2 to 3 weeks, at a depth of 60 cm, is attributed to NO2− produced by reduction of NO3− at anoxic microsites within the profile. Evidently, a cyclic oxidation and reduction of nitrite and nitrate, occurring simultaneously, is responsible for growth of nitrite oxidizers in the profile.

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Entstehung und Hintergründe der im Stahlbau bis heute bewährten Regeln zur Absicherung gegen Sprödbrüche stehen am Anfang dieser Übersicht. In der Folge ist parallel zur Entwicklung bruchmechanischer Methoden eine enorme Verbesserung der Zähigkeitseigenschaften der Stähle zu sehen. Beides findet seinen Niederschlag in Entwürfen für die Empfehlungen zur Stahlauswahl. Dazu liegt ein Vergleich mit den bestehenden Regeln nahe, wobei auch über Versuchsergenisse zu berichten ist.

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