ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Regulatory guidelines in several western states require that diethylenetriamine pentaacetic acid (DTPA) be used as an extracting agent for estimating the availability of several elements in natural soils, reclaimed mine soils, and strip mine overburden. Because different sample preparation methods may result in conflicting analytical results, the effects of different methods of sample preparation are compared for DTPA extraction of cadmium, cobalt, copper, iron, manganese, nickel, lead, and zinc from soil. Samples of A- and C-horizon soils, with known diverse chemical properties, were collected at 21 localities in unglaciated portions of the Northern Great Plains. Each sample was split into three parts. One part was disaggregated to <10 mesh; the second was disaggregated and ground to <100 mesh; and the third was disaggregated and sieved, the <100 mesh portion being retained. The concentration of elements in the DTPA extracts of the samples prepared in these three ways varied by element and by method of preparation. Consistently, for all methods of sample preparation and in both soil horizons, the effect of sample preparation was not significant for nickel; was significant for iron and manganese; and, for cadmium and cobalt, analytical imprecision invalidated the results. Inconsistent results were obtained for copper, lead, and zinc either between methods of preparation or between soil horizons. Significant linear equations relating the various methods were obtained for copper, iron, manganese, nickel, lead and zinc, but, because of poor analytical precision, not for cadmium and cobalt.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

The rate of N2fixation was evaluated in four experiments using Crowley silt loam soil incubated under flooded conditions. When a flooded soil not planted to rice was incubated under light for a period of 2 yr, the N2fixation rate, as determined by15N tracer, was 57 μg/g/yr, whereas the N2fixation rate measured by the increase in total N content was 61 μg/g/yr. Dinitrogen fixation rate, measured by the acetylene reduction method, was increased considerably when N-poor rice straw was added to the soil. In undisturbed soil cores taken from a rice field,15N fixation was relatively low in relation to the plant's need, occurring only under light and only in the surface layer of soil. Aquatic weeds growing in these soil cores contained appreciable amounts of15N. Measurement of N2fixation by the acetylene reduction method in plexiglass enclosures in the field also showed a low fixation of N2.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Heterotrophic nitrogen fixation, as influenced by water treatment, cellulose, and ammonium sulfate was investigated in four tropical, Indian rice soils; the15N tracer technique was used for the first time. Despite high salinity and acidity, appreciable nitrogen fixation occurred in the acid sulfate and the saline soils under both flooded and nonflooded conditions. Soil submergence accelerated nitrogen fixation in all soils. Addition of cellulose to both nonflooded and flooded soils enhanced nitrogen fixation. In flooded alluvial and laterite soils, nitrogen fixation decreased with increasing concentrations of ammonium sulfate; under nonflooded conditions, this inhibition was more pronounced, particularly in laterite soil. Nitrogen fixation was completely inhibited by ammonium sulfate in the acid sulfate and the saline soils.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

A replicated pot experiment was conducted to study the effect of five levels of fluorine (0, 25, 50, 100, and 200 ppm F) and four levels of phosphorus (0, 25, 50, and 100 ppm P), applied to a rice crop grown in soils of two sodicities, exchangeable sodium percentage (ESP) 30 and 70, on their transformations in soil and uptake by a subsequent wheat crop. Application of fluorine resulted in increased water-extractable fluorine in the soil, the relative increase being greater in soil of high ESP, which was associated with high pH. Fluorine uptake by plants increased linearly (r= 0.89) with increased water-extractable fluorine in the soil, and this resulted in a significant reduction in the wheat yield. A fluorine content of 35 ppm in mature wheat straw, which was associated with 22 ppm of water-extractable fluorine in the soil, was observed to be the critical concentration for grain yield. Higher uptake of fluorine by the plant resulted in increased uptake of sodium although composition in respect of other constituents remained unaffected.Application of both phosphorus and fluorine resulted in higher extractability of each other in soil, the relative increase being more at higher fluorine levels. The effect of phosphorus on soil fluorine was more marked at low than at high ESP. From the results it seems that while there is a positive effect of phosphorus on soil fluorine, it has a negative effect on its uptake by the plant. Increasing phosphorus in the soil and in the plant resulted in marked reduction in the chlorine content of the plant (r= 0.79).

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Fluorescein and pyranine were used as solute markers in field experiments under irrigation and under winter rainfall. Dye distribution was recorded by ultraviolet photography and was also measured from analyses of soil extracts.Ultraviolet photographs showed uneven horizontal distribution of fluorescein. The main causes were (1) earthworm channels, which appeared to be more important for solute transport under irrigation than under winter rainfall; (2) fissures about 0.05 to 0.10 millimeters wide; and (3) loosely packed soil with varied pore sizes. Although the dye was adsorbed by soil, the vertical distribution followed a similar pattern to that of chloride, suggesting that it was conducted down the same channels as more mobile solutes.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Laboratory humification experiments were carried out at 27°C and 95 percent relative humidity starting from sawdust, either alone or mixed with different materials, and using watered soil extract as a primer. Increasing yields of humified matter were obtained by the following additions: NH4NO3< sawdust alone < NH4NO3+ sucrose < NH4NO3+ CaCO3< sucrose < CaCO3< NH4NO3+ CaCO3+ sucrose < CaCO3+ sucrose < casein + sucrose < casein + CaCO3+ sucrose < casein < casein + CaCO3. Also, the most favorable molecular size distribution of the humic fractions, with reference to the promotion of the stability of soil structure and to the efficiency of nutrient uptake by roots, was that obtained by incubation of sawdust with casein + CaCO3.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Factors affecting anaerobiosis in soil have been studied by means of computer simulation applied to a model soil composed of spherical aggregates in a hexagonal packing. This schematized geometry implies that two different types of pores are distinguished: intra- and interaggregate pores. The moisture characteristics for the interaggregate water and the non-water-covered area of the aggregates, the so-called air-exposed area, were calculated in general terms. The results give a tool to derive curves for a certain aggregate radius. The interaggregate water content is used to calculate the diffusion properties of the model soil down the profile. The diffusion from interaggregate pores into the aggregates is taken proportional to the air-exposed area of the aggregates.Results of the model are given for an aggregate radius of 0.5 centimeters. They indicate anaerobiosis to occur below a depth of 10 centimeters and in the profile as a whole, before and during rainfall, respectively. The anaerobic soil volume rapidly responds to a shower of rain. However, it is not affected as seriously by the water regime as it is by the magnitude and distribution of the respiratory activity or the diffusion coefficient in the aggregates. The model soil was also used to derive, for a particular case, a soil anaerobiosis characteristic relating soil moisture suction to the anaerobic soil fraction. Some indications are given for further experimental research.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

A technique was developed to partition the soil profile of plotted plants ofAtriplex confertifoliaso that soil water condition could be controlled at specific depths. During an experiment in August in a field environment, plant water status was more stressed when soil water availability was restricted to the top 10 centimeters of the profile compared to the deeper 30 to 40-centimeter zone. Soil water was more beneficial, however, when it was available throughout the profile.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

A modified apparatus that permits measurement of hydraulic conductivity of undisturbed soil cores in the laboratory is described. In this technique the two traditional errors, i.e., side flow and destruction of soil structure, are simultaneously controlled. The results obtained are significantly lower and more realistic than those of the traditional technique.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID