Methylene Blue Spot Test for Cation Exchange Capacity (CEC) Estimation in Acid Soils of India

Abstract

In order to establish a simple, rapid and cost effective method of estimating cation exchange capacity (CEC) of acidic soils, we tested the utility of methylene blue spot test (MBST) vis-à-vis commonly used neutral 1N ammonium acetate method (NAAM) in twenty acidic soils. The soils collected from ten different states of India varied widely in pH, organic carbon content and texture. Averaged across the soils, MBST-CEC was 37% lower than the NAAM-CEC, due possibly to the differences in pH at which the two methods operate. The CEC values estimated by MBST correlated strongly (R=0.89) with those obtained by NAAM, implying that MBST can be used satisfactorily to measure CEC of acidic soils. An equation for inter-conversion of CEC values obtained by the two methods was also worked out. Since NAAM is a time taking and tedious procedure, we recommend MBST method for routine estimation of CEC in acidic soils of India. The method is easily applicable with simple test equipments including filter papers, a glass rod or dropper and methylene blue dye. More than 60 samples a day can easily be analyzed for CEC using MBST method. Being a simple, rapid and cost effective method, the MBST can be included in rapid soil testing kits. Given the importance of CEC in soil fertility and plant nutrition, MBST-CEC may also be included in the soil health cards distributed to the farmers.