The Hertz Corporation

About: The Hertz Corporation is a based out in . It is known for research contribution in the topics: Population & Soil water. The organization has 9562 authors who have published 11044 publications receiving 447929 citations. The organization is also known as: Hertz Rental Car & Hertz Rent-a-Car.

Kinetic study of the retrogradation of gelatinised starch

Abstract: A method was developed for the study of starch retrogradation by differential thermal analysis. The kinetics of the crystallisation process were studied using the expression θ8 = exp (-ktn), where θ = the fraction of crystallisable starch remaining uncrystallised at time t. The values for the Avrami exponent (n) and the rate constant (k) were found to coincide with values previously obtained for the staling of bread, as followed by measurement of crumb elastic modulus. No difference between the time constants of gels cooled slowly and rapidly after gelatinisation was found, indicating that the nucleation process in starch crystallisation is instantaneous in the systems studied. The fact that the Avrami exponent is unity also suggests that the nucleation process is instantaneous, and that it is followed by rod-like growth of crystals.

Is the dehydrogenase assay invalid as a method to estimate microbial activity in copper-contaminated soils?

Abstract: Soil dehydrogenase activity is commonly estimated from the conversion of triphenyltetrazolium chloride (TTC) to triphenylformazan (TPF). There are many reports of larger proportional decreases in dehydrogenase activity than in other indices of microbial activity in Cu-contaminated soils or in soils recently amended with Cu-contaminated sewage sludge. We describe four experiments which measured the effects of Cu on the dehydrogenase assay. In the first, soil microbial biomass, soil dehydrogenase activity and biomass specific dehydrogenase activity were compared in a soil contaminated with heavy metals, including Cu, and in an uncontaminated soil. The specific dehydrogenase activity of the biomass was about 35% less in the metal-contaminated soil than in the uncontaminated soil. In contrast, previous work showed that the biomass specific respiration rate was about 1.5 times faster in the metal-contaminated soil. In the second experiment, sewage sludges (uncontaminated, contaminated singly with Cu, Ni, Cd or Zn and a sludge containing the metals in combination) were added separately to an uncontaminated soil and incubalcd for 7 days at 25°C. Large, similar increases in biomass C, CO2 evolution and biomass specific respiration were measured within all sludge-amended soils at 1 and 7 days after sludge addition. Soil dehydrogenase activity increased similarly in the soils amended with sludges which contained no added Cu. Thus the specific dehydrogenase activity of the biomass was very similar in all these treatments. In contrast, soil dehydrogenase activity and specific dehydrogenase activity of the biomass in the soils amended with Cu-rich sludge or with the sludge containing all the metals, including Cu, were 2–3 times smaller than in the other treatments. In the third experiment, TPF was incubated with separate solutions (0–100 mg l−1) of heavy metals in the absence of soil. Absorbance of TPF was virtually unaffected at any concentration of Ni, Cd or Zn but declined almost to zero between 0 and 20 mg Cu l−1. If this abiological reaction occurred in soil it would be reported, incorrectly, as decreased dehydrogenase activity. This was tested in the fourth experiment by adding TPF to soils previously incubated with the various metal-rich sludges. Absorbance due to TPF was significantly decreased in the soils containing Cu-rich sludges, but was unaffected in the other treatments. It thus appears that the main reason why soils contaminated with Cu apparently have significantly decreased dehydrogenase activities is the abiological reaction between TPF and Cu. Previous research on the effects of Cu on soil dehydrogenase activity has not considered this phenomenon and much of it, therefore, is probably invalid.

Determination of ammonia and nitrate in soil

Abstract: 1. Methods for the determination of ammonia and nitrate in soil are described. The ammonia and nitrate are extracted at pH 1·0–1·5 with a mixture of potassium sulphate and sulphuric acid, and the ammonia is determined by distillation with magnesium oxide at 25° C. in a modified Conway microdiffusion unit. Ammonia plus nitrate is determined on a separate sample of the same extract by reduction of the nitrate to ammonia with titanous hydroxide and subsequent distillation with magnesium oxide, both the reduction and distillation being carried out in a modified microdiffusion unit at 25° C.2. The methods are applicable to coloured extracts and are not affected by substances found to interfere with other methods of determining ammonia and nitrate.3. It is suggested that the methods may also prove useful for the determination of ammonia and nitrate in plant materials.

Soil conditions and the take‐all disease of wheat

Abstract: SUMMARY A study has been made of the decline in viability of Ophiobolus graminis as resting mycelium in artXcialIy infected wheat straw buried in the soil. The pieces of straw were buried in variously treated soils set up in glass tumblers, and were examined at intervals for the presence of still viable Ophiobolus mycelium by means of a wheat seem test. The experimental results suggest that the disappearance of Ophiobolus from the straws was due to natural decomposition by the other soil microorganisms since, in its resting phase, the fungus tolerated adverse physical conditions of the soil better than conditions optimum for microbiological activity. Decline in viability of the fungus appeared to be indefinitely postponed in air-dry soil, in soil at 2–3°C., and under sterile conditions in the culture flask; it was less rapid in a waterlogged soil than in one maintained at medium moisture content. The soil conditions least favourable for the advance of Ophiobolus along the host roots in its parasitic phase (Garrett, 1936) may best preserve it during its resting phase because they are also unfavourable for general microbiological activity. Loss of viability was hastened by the addition of energy materials poor or entirely lacking in nitrogen, such as glucose, starch, and rye-grass meal, to the soil; it was more rapid in a partially sterilized and reinoculated soil than in an untreated soil. These results may be attributed to the rise in numbers and activity of soil micro-organisms following upon the treatments. The rate of decline of the fungus varied with soil type, being more rapid in rich and heavy soils than in poor, light soils. Rate of decline was apparently not directly affected by soil reaction, nor appreciably by moisture content of the soil over the range 30–80% saturation. Decline of the fungus was more rapid under conditions of fluctuating soil moisture and improved aeration in unglazed flower-pots than under more uniform conditions in glass tumblers; it was slowest in soil maintained under still and uniform conditions in a small closed incubator. The most rapid disappearance of the Ophiobolus resting mycelium, therefore, seems to have been secured by conditions favouring maximum microbiological activity in the soil. The decline in viability of the fungus did not necessarily proceed parallel with gross decomposition of the infected straw as a whole. It was delayed by the addition of dried blood, containing 13% nitrogen, to the soil, whereas this treatment accelerated decomposition of the straw. Decline of the fungus was accelerated by addition of rye-grass meal, which delayed decomposition of the straw by taking up the available nitrogen. It is suggested that the Ophiobolus mycelium may itself serve as a source of nitrogen for the decomposition of the straw, and that the rapidity of its disappearance may be related directly to the degree of nitrogen scarcity in the soil and straw medium. I have much pleasure in thanking Dr A. G. Norman for various useful suggestions, and for all the nitrogen determinations. I am especially indebted to Miss L. Cunow and to Miss M. M. Browne for help in the carrying out of the experiments.