Field method for the determination of molybdenum in plants

This paper examines the use of short extraction times, and the determination of aluminium with chrome azurol S (CAS), for the estimation of 0.02 M CaCl2-soluble aluminium in soils. It reports the correlation between CAS-reactive aluminium in 5 min extracts and percent maximum yield of white clover (Trifolium repens) for a series of acid soils. The reactivity of soluble and colloidal aluminium species with the metallochromic reagent CAS has been assessed. ~ l ( a q ) ~ + , simple hydroxy species and complexes of weakly binding ligands (salicylic acid, tannins) are CAS-reactive (2 rnin). In contrast, complexes of strongly binding ligands (citric acid, fulvic acid) are not CAS-reactive ([Al] ~ [L] ~ [CAS] ~ 1-2~10-5 M). For a series of six limed phosphated topsoils and subsoils (pH 4.2-5.5), 0.02 M CaCl2- soluble aluminium, as determined with CAS, was negatively correlated against the percent maximum yield of white clover; r2 = -0.73** (5 min extraction), n = 20. This correlation is similar to that for yield against total aluminium as determined by atomic absorption spectroscopy after 60 min extraction (r2 = -0.77**). However, the colorimetric analysis is more convenient and sensitive; further, it does not measure colloidal and polymeric aluminium species (which may not be plant-available). The satisfactory correlation achieved for short extraction times suggests use of CAS for a rapid field method for aluminium toxicity in soils.

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Field method for the determination of aromatic primary amines in air. Part II. Development of a sensitive field test

The Analyst ◽

10.1039/an9810601088 ◽

1981 ◽

Vol 106 (1267) ◽

pp. 1088 ◽

Cited By ~ 3

Author(s):

D. W. Meddle ◽

A. F. Smith

Keyword(s):

Field Test ◽

Field Method ◽

Primary Amines

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Determination of bearing capacity of shallow foundations without using superposition approximation

Canadian Geotechnical Journal ◽

10.1139/t02-105 ◽

2003 ◽

Vol 40 (2) ◽

pp. 450-459 ◽

Cited By ~ 18

Author(s):

D Y Zhu ◽

C F Lee ◽

K T Law

Keyword(s):

Bearing Capacity ◽

Field Method ◽

Ultimate Bearing Capacity ◽

Shallow Foundation ◽

Closed Form Expression ◽

Safe Side ◽

Superposition Approximation ◽

Bearing Capacity Factor ◽

Rigorous Procedure

The Terzaghi superposition assumption has been widely used to determine the bearing capacity of shallow footings. Although this assumption always errs on the safe side, a rigorous procedure to calculate the bearing capacity is still of engineering value. This paper presents such a procedure that is free from errors as a result of the superposition assumption. It demonstrates that the ultimate bearing capacity can be precisely expressed by the Terzaghi equation, except that the bearing capacity factor Nγ is dependent upon the surcharge ratio. A recently developed numerical method, i.e., the critical slip field method, is used to calculate the modification coefficient for modifying Nγ. It is found that this modification coefficient increases with the surcharge ratio at small values of surcharge ratio and then remains constant for large values of surcharge ratio. However, the errors invoked by the superposition assumption do not exceed 10%. On the basis of numerical calculations, a simple closed-form expression of the modification coefficient is proposed that yields the theoretically rigorous ultimate bearing capacity. In the later part of the paper, errors in bearing capacity calculations owing to the use of conventional procedures are analyzed. It is concluded that the continued use of conventional procedures is justified, but the inherent errors should not be neglected in assessing the performance of shallow foundations.Key words: shallow foundation, strip footing, ultimate bearing capacity, critical slip field.

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