Phytotoxicities of nicosulfuron and atrazine residues in soil on sweetpotato

To clarify the phytotoxicity of nicosulfuron and atrazine residues in the soil of corn fields on the growth of sweetpotato in the next year, the soil samples from sweetpotato fields were collected from Mancheng District of Baoding City, Wen’an County, Bazhou City and Gaocheng District of Shijiazhuang City of Hebei Province. The QuEChERS with ultra-performance liquid chromatography-mass spectrometry (UPLC-MS/MS) was used to determine their residues. The phytotoxicity of nicosulfuron, atrazine and their mixture in the soil on sweetpotato was evaluated in the pot experiments. The results showed that the residues of nicosulfuron in the soil of sweetpotato fields in Mancheng District of Baoding City, Wen’an County, and Bazhou City, of Hebei Province with severe phytotoxicity were 11.80-87.97 μg/kg soil, and the atrazine residues were 2.71-8.40 μg/kg soil. Only atrazine with the contents of 3.43-4.42 μg/kg soil was detected in the non-phytotoxic sweetpotato field in Gaocheng District of Shijiazhuang City, Hebei Province. The results of pot experiments with different herbicide treatments showed phytotoxic symptoms of sweetpotato 20 days after the treatment of 1 μg or more nicosulfuron per kilogram of soil. The IC₅₀ value of nicosulfuron to roots was 3.74 μg/kg soil, while the IC₁₀ value was 1.27 μg/kg soil. Atrazine in the range of 2-40 μg/kg soil have no visible phytotoxicity on the aboveground and underground parts of sweetpotato, but have slight inhibitory effect on the growth of the root system. The combination of nicosulfuron and atrazine in the ratio of 10 : 1, 5 : 1, 5 : 2 and 5 : 5 had antagonistic effect on sweetpotato phytotoxicity. Their co-toxicity coefficients CTC₅₀ value were 66.25, 59.16, 61.30 and 79.47, respectively. The phytotoxic symptoms of nicosulfuron to sweetpotato included plants stunted, leaf blade smaller, whole plant or new leaves yellowish, rootlet development reduced, lateral roots short and thick. These results suggested that nicosulfuron is the main factor caused the phytotoxicity of sweetpotao, and its phytotoxic threshold was 1 μg/kg soil.