Summary
The addition of 2.5 mg/l of polyacrylamide to 0.5M NaHCO3 used as an extractant for ‘available’ phosphate overcame most of the analytical difficulties associated with the use of activated carbon which was recommended in the original procedure of Olsen et al. (1954). No significant differences in the amount of P extracted were found between polyacrylamide and carbon and with the former, technical problems were greatly reduced. Consequently, the modification of the original method to incorporate polyacrylamide has been adopted in the Agricultural Development and Advisory Service of the Ministry of Agriculture, Fisheries, and Food as a standard method for the determination of available phosphate in soils.
A colorimetric method, using o‐tolidine, for the determination of small amounts of chlorate in soil and plant extracts is presented. Substances known to interfere in the colorimetric procedure are unlikely to be present in significant amount in soil and plant extracts, but if present, compensation for their effects can be made. Examination of different parts of the plant showed that conducting tissue was the most suitable for chemical analysis, although the lamina or the whole plant can be used provided the extract is shaken with activated charcoal. Some observations on several plant species grown in pots containing soil contaminated with chlorate are given.
The method is useful for confirming visual diagnosis of chlorate toxicity in plants and for measuring the residual concentration in the soil.
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