Decontamination of Chlorate in Longan Plantation Soils by Bio-Stimulation with Molasses Amendment

Potassium chlorate is widely used as an active substance for flower induction in longan plantation fields for off-season production of longan fruits in northern Thailand. Contamination of groundwater with residual chlorate in soil is a cause for concern because of its toxicity to human health. Based on our previous finding that the addition of glucose or sucrose to soil was effective for accelerating the disappearance of residual chlorate in soil, the effect of the addition of molasses, which contains a high concentration of sucrose, as a substitute for glucose or sucrose was examined in laboratory and pot experiments. Under laboratory conditions, the addition of molasses to soil at the concentrations of 100 to 200 g kg⁻¹ soil strikingly enhanced the rate of disappearance of chlorate applied at 341 mg kg⁻¹ soil. Addition of diluted molasses was also effective for the accelerated disappearance of chlorate in soil when 33 g kg⁻¹ soil of molasses was added repeatedly. The effect of repeated addition of diluted molasses to soil on the decontamination of residual chlorate in soil was also confirmed in an outdoor pot experiment. These results may lead to the development of a practical method of cleaning-up chlorate-polluted soil in longan plantation fields.