Comparison of several methods for determining free iron in soils

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.