Boron Fixation and Its Release in Soils and Bark Compost

Abstract

Batch studies were conducted to investigate the fixing and release behavior of boron (B) in the soils from Haruo-cho, Kochi, and a bark compost (BC). Boron fixation on river sand (RS) was extremely low. The amount of B fixed was 6.3 mg kg−1 for the greenhouse soil (GS). However, BC showed a 10-fold higher fixation of B (64.1 mg kg−1) compared to GS, indicating that BC here displayed a significant capacity for B trapping. In GS, only around 9% of the adsorbed B was released during a 1-month period of incubation. Bark compost showed the highest amount of release during the incubation period, accounting for 64% of the adsorbed B. Moreover, the ratio of B release increased to 77% in the case of the soil mixed with BC. These results, suggest that different kinds of fixation-releasing mechanisms operate in the soil and BC. The B fixation on soil is considered as specific adsorption on minerals. A possible mechanism for B fixation on BC is ligand exchange. B-diol complexes might be formed with BC, and then after decomposition by microorganisms, they may release B during the incubation period.