Teruo Asami

A new method for determining free iron in paddy soils

Abstract For pedological or edaphological study, it is very important to find a suitable method for determining free iron in soils. The removal of free iron also facilitates the identification and determination of minerals present in soils and clays by X-ray and thermal analysis and microscopic observation. Up to the presnt time many methods have been proposed for the removal or the determination of free iron in soils and clays. With some exceptions these methods are all based on the principle that the free iron compounds existing mainly as ferric iron in soils are reduced to ferrous iron and extracted with suitable reagents. A short historical review is as follows.

Formation of Methyl Mercaptan in Paddy Soils (II)

Abstract In the previous paper1), the authors proposed a method for determining methyl mercaptan formed in paddy soils. In this method, methyl mercaptan was expelled by nitrogen gas from Paddy soils, and was introduced into 4% mercuric CYanide solution after separation from hydrogen sulfide by hydrous calcium chloride and lead acetate (solid). The methyl mercaptan caught by mercuric cyanide solution was measured by colorimetric method using dimethyl-p-phenylenediamine and ferric chloride solutions. And then, the analysis of several field soils was conducted by using this method.

Beryllium contents of uncontaminated soils and sediments in Japan

Beryllium and aluminum contents of uncontaminated soils (27 soil profiles including 129 horizons) and sediments (8 sediments including 49 layers) in Japan were determined. Means, standard deviations. and ranges of beryllium (oven dry matter) were as follows: surface soils except AO horizons (N = 27), 1.17 ± 0.43 (0.27–1.95) μg/g; subsoils (N = 97), 1.35 ± 0.52 (0.34–3.49) μg/g; all soil horizons except AO horizons (N = 124). 1.31 ± 0.51 (0.27–3.49) μg/g; surface sediments (N = 8), 1.36 ± 0.60 (0.65–2.40) μg/g; subsurface sediments (N = 41), 1.28 ± 0.49 (0.50–2.25) μg/g; all sediment layers (N = 49), 1.29 ± 0.50 (0.50–2.40) μg/g. The correlation coefficient between the contents of beryllium and aluminum in these soils and sediments was 0.567 (p<0.001).

Comparison of several methods for determining free iron in soils.

Abstract In the previous paper (1), for determining free iron in paddy soils the writers proposed a new method in which free iron was removed by reduction with sodium hydrosulfite in disodium ethylendiamine tetraacetate solution. As described in that paper, many methods have been proposed up to the present time. In this paper the writers are to compare their method with some of those methods, especially with both methods using sodium hydrosulfite and dilute hydrochloric acid and using hydrogen sulfide and dilute hydrochloric acid. The latter method has generally been employed for free iron determination of paddy soils in Japan.

SOURCE OF NITROUS ACID VOLATILIZED FROM UPLAND SOILS

In order to identify the source of nitrous acid volatilized from upland soils, two experiments were carried out: a 15N tracer experiment and an experiment on the effect of a nitrification inhibitor (thiourea) on nitrous acid volatilization. The following results were obtained. 1) The contribution rate of ammonium-N to the total nitrite-N volatilized was 63–64% in the Taki soil and 61–69% in the Matsuzawa soil, and that of nitrate-N was 23–26% in the Taki soil and 15–18% in the Matsuzawa soil. Recovery of 15N was about 92–96% in both soils. 2) In both soils, the amounts of nitrous acid volatilized decreased by the addition of thiourea. The addition of thiourea-N at a concentration of 10% of the added ammonium-N almost completely suppressed the oxidation of ammonium-N to nitrite-N and nitrate-N in both soils. From these results, it is concluded that a large part of the volatilized nitrous acid originated from ammonium-N.

Volatilization of Nitrous Acid from Upland Soils

In order to identify the chemical form of the toxic nitrogenous gas volatilized from upland soils especially from vinyl house soils, laboratory experiments were carried out with two Andosols collected from vinyl houses in Ibaraki Prefecture. Results were as follows. 1) Nitrite ion was detected in the alkaline absorbents which absorbed nitrogenous gas volatilized from the soils, but nitrate ion was not detected in these absorbents. 2) The same amount of nitrite-N and nitrate-N was found in the alkaline solution which absorbed nitrogen dioxide (NO2) gas. 3) When sodium nitrite was added to the buffer solutions with various pH (4, 5, and 6), nitrogenous gas volatilization occurred even at pH 6, and nitrite ion was found in the alkaline absorbents whereas nitrate ion was not detected. From the results obtained, it is suggested that nitrous acid is the chemical form of the nitrogenous gas volatilized from upland soils.