Asian Journal of Soil Science and Plant Nutrition

Aims: The aim of the study was to determine the concentration of soluble Cd and selected chemical properties after the application of humic acid in Inceptisols and Entisols.

Study Design: The experiment used a completely randomized design (CRD) with 2 factors. The first factor was the soil sample (Entisols and Inceptisols), while the second factor was the rate of humic acid application, consisting of 0 g kg^-1 (control); 10 g kg^-1; and 20 g kg^-1.

Place and Duration of Study: The experiment was located in Soil Science Laboratory, Faculty of Agriculture, University of Bengkulu. Inceptisols were collected from Seginim, Air Nipis District, South Bengkulu Regency, Bengkulu Province and Entisols were sampled from Muara Bangka Hulu District, Bengkulu Province. Each treatment combination was repeated three times.

Methodology: Three hundred g of soil was treated with 100 mg kg^-1 Cd and placed in a 500 ml plastic glass. Humic acid was added according to the treatment and mixed homogeneously. The sample was maintained at field capacity moisture content by adding distilled water every day. Medium pH was monitored every week.

Results: Results showed that the application of humic acid to the rate of 20 g kg^-1 did not significantly reduce the solubility of Cd. Nonetheless, humic acid at the same rate increased soil pH by 23%, organic-C by 32% and CEC by 45% compared with the control. Entisols had higher soil pH and organic-C but lower CEC than Inceptisols. The concentration of soluble Cd was not significantly different between the two soil samples.

Conclusion: The findings indicates that while humic acid improves vital soil chemical properties, its effectiveness in immobilizing Cd may be dependent on application rate and soil types. Further optimization of humic acid formulations and management practices is necessary to improve Cd-contaminated soils.