Abstract: Golden apple snail (Pomacea canaliculata) is one of the 100 worst invasive alien species cognized by World Conservation Union, and has been resulting in a mass loss of rice production in South China. In this study, the snails accoding to their shell height (H) were divided into four groups, i.e., small size (5 mm≤H<15 mm), medium size (15 mm≤H<25 mm), large size (25 mm≤H<35 mm), and extra large size (35 mm≤H<45 mm), and a laboratory toxicity test was conducted to evaluate the molluscicidal activity of chemical fertilizer calcium cyanamide (CaCN₂) in controlling different sizes P. canaliculata. Calcium cyanamide had significant molluscicidal effect on different sizes, especially small and medium sizes P. canaliculata. After treated one week, 0.2 g·L^-1 of CaCN₂ induced 71% mortality, and high concentrations CaCN₂ resulted in above 95% mortality, with 100% mortality in treatments 3.0 g·L^-1 and 5.0 g·L^-1 of CaCN₂. Both the 24 h median inhibitive concentration and the 96 h median lethal concentration of CaCN₂ on different sizes P. canaliculata were all in the order of small size < medium size < large size < extra large size. Calcium cyanamide had significant inhibitive effect on P. canaliculata. The mean inhibitive concentration of CaCN₂ ranged from 0.08 g·L^-1 to 0.39 g·L^-1. After treated 24 h, the SOD activity of P. canaliculata in treatments 1.0 g·L^-1 and 5.0 g·L^-1 of CaCN₂ decreased significantly, being 41% and 60% of the control, respectively. This study showed that calcium cyanamide had definite potential in controlling P. canaliculata invasion, being hopeful to be used as a kind of molluscicidal fertilizer in paddy field.

Key words: Metsulfuron-methyl, Herbicide, Soil, pH, Microbial activity