Field testing labile soil organic carbon using potassium permanganate in tropical soils

Dr Wipawan Thaymuang1, Miss Aunthicha  Phommuangkhuk1, Miss Sirisuda   Bootpetch1

1Department Of Soil Science, Faculty of Agriculture at Kamphaeng Saen, Kasetsart University, Kamphaeng Saen, Thailand

Permanganate (KMnO4) was used to test for oxidizable organic carbon (POXC) as labile soil organic carbon. Soil samples were collected from five different soil types based on clay mineral types; kaolinite, kaolinite+iron oxides, smectite, siliceous, and mix. Active soil organic matter was estimated visually in a range consisting of 6 levels (0.5%, 1%, 1.5%, 2%, 2.5% and >3%) of KMnO4 to evaluate the quantity of active soil organic matter using the visual solution color of deep purple color (<0.05%OM) to a lighter KMnO4 solution color (>3%OM) based on comparison with the RHS color chart. Then, the color chart was modified based on the percentage of organic carbon compared with Walkley and Black method (the routine method). The results showed that the POXC color chart was strongly correlated with the percentage of organic carbon based on the routine method in all clay mineral types. Where the red color of a clay soil had been interfered by iron oxides added as flocculants or had been allowed to stand for a longer period (10-20 min), the solution became clear. However, about 75% of all samples, potassium permanganate was able to evaluate the quantity of labile soil organic matter in same-colored shades of soil samples with different organic carbon based on the routine method. The relationships to potassium permanganate oxidized organic carbon occurred in clay mineral types and amount of organic carbon. These results suggest that this method can be used as a labile organic matter test kit that is quick and inexpensive to evaluate active soil organic carbon content in the field for use in nitrogen fertilizer recommendations.

Key words: Labile Soil Organic Carbon Test Kit, Potassium Permanganate, Tropical Soils


I received B.A. and M.S. in Agriculture (soil science) in 1997 and 2001 respectively, and Ph.D. in Soil Science in 2013 from Kasetsart University that focus on the stabilization of soil organic matter by iron oxides in highly weathered Tropical Soils.

I have worked for Department of Soil Science, Kasetsart University, since 2001.

My research focus on interaction between clay mineralogy and organic matter, labile and stabilization of soil organic matter in Tropical Soils, including soil fertility and plant nutrient management for crop production such as rice, corn, and sugarcane.

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