The extraction of Al, Fe and Si from a range of New Zealand soils by hydroxylamine and ammonium oxalate solutions

Abstract

The elements Al, Fe and Si were extracted with acid oxalate and acid (HCl) hydroxylamine by using 36 samples from eight different soils, and the results for each extractant were compared. Parent materials were largely volcanic in nature, but eight samples were from soils derived from quartzo-feldspathic materials. Oxalate extracted significantly greater amounts of Fe from most samples than hydroxylamine. Results for Al and Si were less consistent. Compared with oxalate, hydroxylamine (soil : solution, 1:250) extracted significantly greater amounts of Al and Si from some samples and less from others. Taken over all samples, however, there was no significant difference between the two methods in the amounts of Al and Si each extracted. A decrease in the soil:solution ratio for hydroxylamine from 1:250 to 1:400 had little effect of Fe and Si values, but it did increase the amount of Al extracted in several cases. Soil mineralogy appeared to bear little relationship to observed differences, although the presence of magnetite probably contributed to higher oxalate-Fe values. Although statistically significant, differences between individual values were generally small. Results are compatible with previous studies which indicated that hydroxylamine provides an approximation of oxalate values for Al and Fe. Unlike previous work, however, the present results also suggest that approximate values can be obtained for Si.