Browsing by Author "S. SINGH"

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STUDIES ON HUMIC ACIDS OF SEVEN TYPICAL SOILS OF RAJASTHAN
(1965) S. SINGH; G.S. BHANDARI
Humic acids from seven different cultivated irrigated soils of the semi‐arid and arid regions were extracted with N/2 NaOH and were analysed for their elementary composition and cation exchange capacity. The methoxyl contents of the cids were determined before and after methylation. There were marked differences in the carbon and nitrogen and in the ash constituents of the acids obtained from different soils. The humic fractions obtained from three darkgrey soil types had higher carbon and lower methoxyl contents than the others. The nitrogen contents of the fractions from three of the soils were comparatively high, being about 8 per cent. These results show that the humic acids of the darkgrey soils are of a more condensed nature than the others. The hydrogen content varied only a little and was less characteristic of the fractions. The high ash contents of all the humic acids is interesting, the figures ranging from 5.8 to 10.6 per cent. Of the ash 31.7 to 39.5 per cent occurs as silica, 19.7 to 24.6 per cent as alumina, 17.5 to 29.0 per cent as iron oxide, 8.3 to 14.5 per cent as phosphorus pentoxide, and 0.54 to 1.88 as the oxides of calcium and magnesium together. The presence of silica is possibly the result, partly at least, of its dissolution during alkali extraction of the soils so that it is held up by humic‐acid particles on acidification of the extracts. The oxides of iron and aluminium, forming about 50 per cent of the ash, appear to be partly present chelated with the humicacid molecules. The methoxyl content varied with the soil type from 0.3 to 1.6 per cent and was increased by methylation of the humic acids by between 5.3 and 7.8 per cent. Methylated humic acids had a much smaller cation exchange capacity than the unmethylated acids. Copyright © 1965, Wiley Blackwell. All rights reserved