Abstract
The application of organic matter to agricultural soils is believed to be effective for an increase in the cation-exchange capacity (CEC) of soils; however, quite few attempts have so far been made at the detailed charge characteristics of soils affected by long-term organic matter application. The objectives of the present study are to evaluate the CEC and anion-exchange capacity (AEC) of Andisols, where cattle manure and/or crop residues have been incorporated for 25 years, by using the repeated equilibration method, and to reveal the effect of continuous application of organic matter on the charge characteristics of Andisols. The CEC values measured by the repeated equilibration method of the organic matter applied soils were slightly higher than that of the soil without application of organic matter. The differences in the CEC values between these soils were approximately 20% in the slightly acidic range (pH 5.5) and less than 10% in the neutral range (pH 6.5) . When the usual amount of cattle manure (15 Mg ha^<-1>) has been incorporated, the increase in the CEC could not be expected in case of Andisols. On the other hand, the AEC values decreased remarkably with the continuous application of organic matter. These results could be induced by the change in the soil colloidal constituents after the long-term application of organic matter. The greater part of organic matter applied to the fields would remain in soils as microbial-resistant constituents without a positive interaction with soil mineral components. It was supposed that the appearance of the charge characteristics of the remnant organic matter should result in the slight increase in CEC and the remarkable decrease in AEC of Andisols.
