A critical examination of some common field tests to assess the acid‐sulphate condition in soils

Abstract

Acid-sulphate soils are of major environmental concern in many wetlands. Severe acidification episodes have occurred worldwide because of the oxidation of iron sulphides to sulphuric acid by human activities, and diverse techniques have been set up to determine the presence of acid-sulphate soils. This paper evaluates the usefulness of four common easy-to-apply field survey tests for potential acidsulphate diagnosis in some Histosols and Entisols in wetlands: incomplete oxidation by fast air-drying, incubation, fast oxidation with hydrogen peroxide, and the indirect determination of sulphide with lead acetate. Samples of 227 surface-organic and underlying mineral soils of poorly drained Histosols and Entisols of the Orinoco river delta plain were tested. Results showed that for highly organic samples the interpretation of results obtained from the acid-sulphate soil tests may be misleading, because they cannot be unambiguously related to the production of sulphuric acid derived from pyrite oxidation. Mineral samples yielded more reliable results. The incomplete oxidation by fast air-drying test did not induce significant acidification either in organic or in mineral samples; the final pH values were dependent on the original pH values. The fast oxidation with hydrogen peroxide test was effective with mineral samples. During the incubation test, the slower rate of pH decrease and the final values obtained with the organic samples suggested retardation in the rate and amount of acid generation by pyrite oxidation because of the concurrent oxygen consumption by organic matter and bacterial activity. The indirect determination of sulphide with lead acetate yielded only qualitative results in organic samples, but worked well in mineral samples, indicating a higher content of pyrite intermediates. Effective estimation of the actual presence and potential for acidification of soil is important, in order to avoid excessive or inappropriate amelioration techniques to prevent acid production.

The importance of soil carbon and nitrogen for amelioration of acid sulphate soils

“…In places where ASS are present, appropriate management practices need to be employed to minimize soil oxidation and acid production (Vegas‐Vilarrubia et al ., ; Melville & White, ). Strategies focusing on two key principles have been proposed, tested and established (Baldwin & Fraser, ).…”

Impact of land use on Histosols properties in urban agriculture ecosystems of Rio de Janeiro, Brazil

“…In our study, this process is demonstrated by the high correlations between the SO 4 2content, pH values, and ECe ( Figure 7). The observed low soil pH values and the soluble sulfate contents (SO 4 2-) also indicated acid-sulfate soil potential (Vegas-Vilarrúbia et al, 2008).…”

Chemical processes and sustainability of rice-shrimp farming on saline acid sulfate soils in mekong delta

“…[ 35 , 36 ], a simple field test on sulfide materials is as follows: after applying 30% hydrogen peroxide to the fresh sample, within a couple of minutes, it will froth and its pH will fall from neutral to less than 2.5. Although in general, pyrite oxidation generated acidity and proceeded faster in mineral samples [ 37 ], note that the hydrogen peroxide test was not effective for soils with high organic matter content because acidity may have been generated by the oxidation of organic matter to organic acids [ 35 , 37 ], which leads to lower pH values.…”